US20110096320A1 - Laser obstacle ranging and display - Google Patents

Abstract

Apparatus, for detecting at least one object and preventing receiver burn-out, mounted on a vehicle, including a laser and at least one receiver, the receiver being coupled with the laser, the laser for transmitting a beam of light and the receiver for detecting reflections of the beam of light from the object, the laser including at least one signal diode, a commutator, a power supply signal diode driver, a circulator, an erbium doped fiber (EDF), a wavelength division multiplexer (WDM), a narrow band Bragg reflector, a first fiber pump diode, an output combiner and a second fiber pump diode, the commutator being coupled with each signal diode and the power supply signal diode drive, the circulator being optically coupled with each signal diode, the EDF and the output combiner, the WDM being optically coupled with the EDF, the narrow band Bragg reflector and the first fiber pump diode and the second fiber pump diode being optically coupled with the output combiner, each signal diode generating a beam of light distinct from one another, the power supply signal diode driver for supplying energy to each signal diode, the circulator for directing the beam of light in at least one of at least two different directions, the EDF for amplifying the beam of light thereby producing an amplified beam of light, the narrow band Bragg reflector for reflecting only the amplified beam of light through the EDF a second time, thereby producing a double amplified beam of light and the first fiber pump diode and the second fiber pump diode for pumping the EDF, wherein the WDM and each of the signal diodes are located on opposite sides of the EDF, wherein the output combiner outputs the beam of light, wherein the commutator enables each signal diode, one at a time, to draw a predetermined amount of energy from the power supply signal diode driver, wherein one signal diode generates a low energy beam of light and another one generates a high energy beam of light, wherein the low energy beam of light is transmitted by the output combiner before the high energy beam of light, and when the low energy beam of light is detected by the receiver, and the energy level of the low energy beam is above a predetermined threshold, the high energy beam of light is not transmitted.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application claims priority to and is a continuation-in-part of PCT Application No. PCT/IL2006/000080, filed Jan. 19, 2006, which claims priority to Israeli Application No. 166430, filed Jan. 20, 2005 and Israeli Application No. 169402, filed Jun. 26, 2005; each of which is incorporated herein by reference in its entirety.
FIELD OF THE DISCLOSED TECHNIQUE
• The disclosed technique relates to obstacle warning systems in general, and to methods and systems for detecting hard-to-see long and thin obstacles, in particular.
BACKGROUND OF THE DISCLOSED TECHNIQUE
• A major hazard in vehicle operation is the danger of collision with objects which are in the path of the vehicle, and which might not be immediately detectable by the person operating the vehicle. In particular, a hazard in aircraft operation is the danger of collision with ground structures and low-lying obstacles. Overlooking such obstacles, by the aircraft pilot, could result in a crash or a serious accident. Obstacles which are especially difficult to detect by the pilot are, for example, power lines, communication wires, antennas, towers, and the like, which become practically invisible to the pilot in some conditions. Helicopters, in particular, often fly at low altitudes, where ground structures and wires are common, thus the danger of a crash is greater.
• Systems for warning aircraft pilots of obstacles in their flight course are known in the art. Such warning systems are often based on laser light detection and ranging (herein abbreviated LIDAR) assemblies. A LIDAR system scans the flight path in front of the aircraft, with a laser beam, and detects laser reflections from obstacles which are in the observable range of the system. The system alerts the pilot of detected obstacles which lie in the flight path ahead. The pilot then decides on the best way to avoid the obstacles, if necessary.
• U.S. Pat. No. 6,723,975, issued to Saccomanno and entitled “Scanner for Airborne Laser System,” is directed to a laser scanner for a LIDAR system, for scanning a field of view of an aircraft and detecting obstacles. The scanner comprises a plurality of condensing optical elements, a plurality of windows, an optical enclosure, a multiple-axis scanning mirror and light detectors. The optical enclosure is formed by the windows and condensing optical elements. A laser energy source is located externally to the optical enclosure. One of the condensing optical elements includes an aperture, such as a hole drilled there through, so that a laser beam, emitted from the laser energy source, can enter the optical enclosure.
• Laser energy is emitted from the laser source, and enters the optical enclosure, hitting the scanning mirror. The scanning mirror directs the laser energy through the windows of the optical enclosure to a plurality of targets in a field of view. The laser energy returned from the plurality of targets reenters the optical enclosure through the windows, hitting the laser detectors. The reflected laser beam is used to detect obstacles, such as wires, which may be present in front of the aircraft.
• U.S. Pat. No. 6,724,470 issued to Barenz et al. and entitled “Laser Assembly for LADAR in Missiles,” is directed to a two-stage laser beam generating device for a laser-radar (herein abbreviated LADAR) system, for use in target tracking missiles. The device comprises a master oscillator, a laser-fiber coupling lens, a fiber Faraday insulator, an erbium doped fiber amplifier (herein abbreviated EDFA), a diode laser pump, a dichroic mirror, a transmitter fiber and a transmitter. The master oscillator is connected to the Faraday insulator through the laser-fiber coupling lens. The dichroic mirror is placed between the output of the Faraday insulator and a first end of the EDFA. The diode laser pump faces the dichroic mirror, in a manner substantially perpendicular to a line connecting the insulator and the EDFA. A second end of the EDFA is connected to the transmitter through the transmitter fiber.
• The master oscillator, which is a microchip laser, emits a laser beam, which passes through the coupling lens, and enters the Faraday insulator. The laser beam emerges from the insulator, passes through the dichroic mirror and enters the EDFA through the first end thereof. The laser diode pump generates radiation, which is deflected by the dichroic mirror, such that it enters the EDFA through the first end thereof. The amplified laser beam emerges from the second end of the EDFA, into the transmitter fiber. The transmitter fiber then directs the laser beam to the transmitter, which directs the laser beam towards a target.
• U.S. Pat. No. 4,902,127 issued to Byer et al. and entitled “Eye-safe Coherent Laser Radar,” is directed to a laser radar for transmitting eye-safe laser radiation at a target, and detecting reflected laser radiation there from. The laser radar comprises a solid state laser, optical pumping means, optical resonator means, optical amplifier means, transmitter station means, receiver means, a single transverse mode fiber-optic, combining means and detecting means. The laser is coupled to the optical pumping means. The laser is optically coupled to the optical resonator means and to the optical amplifier means. The transmitter station is optically coupled to the optical amplifier means. The single transverse mode fiber-optic is optically coupled to the receiver means. The detecting means is optically coupled to the combining means.
• The laser emits a lasant radiation beam, after being pumped by the optical pumping means. The lasant beam passes through the amplifier before passing through the transmitter. The transmitter illuminates the beam at a target. Reflected radiation from the illuminated target passes through the receiver, and then through the fiber optic. The combining means combines the reflected radiation with a reference coherent lasant radiation. The detector receives the combined radiation from the combiner and detects the differences between the reflected radiation and the reference radiation, the differences being representative of parameters associated with the illuminated target.
• U.S. Pat. No. 6,130,754 issued to Greene and entitled “Eyesafe Transmission of Hazardous Laser Beams,” is directed to an apparatus for preventing injury to humans while transmitting a non-eyesafe (i.e., hazardous) laser beam. The apparatus comprises a non-eyesafe laser source, an eyesafe laser source, a delay component, a receiver/transmitter switch, a deflecting mirror, a dichroic mirror, an optical detector and a trigger. The eyesafe laser source is connected to the receiver/transmitter switch. The delay component is electrically connected to the eyesafe laser source and the non-eyesafe laser source. The dichroic mirror is placed in the path of the eyesafe laser beam. The deflecting mirror is placed in the path of the non-eyesafe laser beam. The optical detector is connected to the receiver/transmitter switch. The optical detector is further connected to the trigger, which in turn is connected to the non-eyesafe laser source.
• The eyesafe laser source emits an eyesafe laser beam, which is deflected by the dichroic mirror. The non-eyesafe laser source emits a non-eyesafe laser beam, after a delay determined by the delay component. The deflecting mirror deflects the non-eyesafe laser beam so that it passes through the dichroic mirror, on the same optical axis as the eyesafe laser beam. After transmitting the eyesafe laser beam, the transmitter/receiver switch is switched to receiving mode. If the detector detects reflections of the eyesafe laser beam (i.e., reflected off an object located in front of the apparatus), then the optical detector disables the non-eyesafe laser source, through the trigger.
SUMMARY OF THE DISCLOSED TECHNIQUE
• It is an object of the disclosed technique to provide a novel method and system for laser obstacle ranging and displaying which overcomes the disadvantages of the prior art.
• In accordance with the disclosed technique, there is thus provided a fiber laser, for detecting at least one object, which includes a signal diode, a circulator, an erbium doped fiber (EDF), a wavelength division multiplexer (WDM), a narrow band reflector, a first fiber pump diode, an input combiner, an erbium-ytterbium co-doped fiber (EYDF), a second fiber pump diode, an output combiner and a third fiber pump diode. The circulator is optically coupled with the signal diode, the EDF and the input combiner, the WDM is optically coupled with the EDF, the narrow band reflector and the first fiber pump diode, the input combiner is optically coupled with the EYDF and the second fiber pump diode and the output combiner is optically coupled with the EYDF and the third fiber pump diode. The signal diode generates a beam of light, the circulator directs the beam of light in at least one of at least two different directions, the EDF amplifies the beam of light thereby producing an amplified beam of light, the narrow band reflector reflects only the amplified beam of light back through the EDF a second time, thereby producing a double amplified beam of light, the first fiber pump diode pumps the EDF, the EYDF amplifies the double amplified beam of light, thereby producing a triple amplified beam of light and the second fiber pump diode and the third fiber pump diode each pump the EYDF. The WDM and the signal diode are located on opposite sides of the EDF and the output combiner outputs the triple amplified beam of light.
• According to another aspect of the disclosed technique, there is thus provided an apparatus, for detecting at least one object and preventing receiver burn-out, mounted on a vehicle, which includes a laser and at least one receiver, the laser being coupled with the receiver. The laser transmits a beam of light and the receiver detects reflections of the beam of light from the object. The laser includes at least one signal diode, a commutator, a power supply signal diode driver, a circulator, an erbium doped fiber (EDF), a wavelength division multiplexer (WDM), a narrow band Bragg reflector, a first fiber pump diode, an output combiner and a second fiber pump diode. The commutator is coupled with each signal diode and the power supply signal diode driver, the circulator is optically coupled with each signal diode, the EDF and the output combiner, the WDM is optically coupled with the EDF, the narrow band Bragg reflector and the first fiber pump diode and the second fiber pump diode is optically coupled with the output combiner. Each signal diode generates a beam of light distinct from one another, the power supply signal diode driver supplies energy to each signal diode, the circulator directs the beam of light in at least one of at least two different directions, the EDF amplifies the beam of light thereby producing an amplified beam of light, the narrow band Bragg reflector reflects only the amplified beam of light through the EDF a second time, thereby producing a double amplified beam of light and the first fiber pump diode and the second fiber pump diode pump the EDF. The WDM and each of the signal diodes are located on opposite sides of the EDF, the output combiner outputs the beam of light and the commutator enables each of the signal diodes, one at a time, to each draw a predetermined amount of energy from the power supply signal diode driver. One signal diode generates a low energy beam of light and another signal diode generates a high energy beam of light. The low energy beam of light is transmitted by the output combiner before the high energy beam of light, and when the low energy beam of light is detected by the receiver, and the energy level of the low energy beam is above a predetermined threshold, the high energy beam of light is not transmitted.
• According to a further aspect of the disclosed technique, there is thus provided an apparatus, for detecting at least one object, the apparatus being mounted on a vehicle, which includes a fiber laser, a motion detector and a controller. The motion detector is coupled with the fiber laser and the controller is coupled with the fiber laser and the motion detector. The fiber laser generates a pulsed beam of light at a certain pulse repetition rate (PRR), the motion detector detects the motion of the vehicle and the controller adjusts the PRR of the pulsed beam of light according to the detected motion.
• According to another aspect of the disclosed technique, there is thus provided an apparatus, for detecting at least one object, the apparatus being mounted on a vehicle, which includes a fiber laser, a motion detector and a controller. The motion detector is coupled with the fiber laser and the controller is coupled with the fiber laser and the motion detector. The fiber laser generates a pulsed beam of light at a certain output peak power, the motion detector detects the motion of the vehicle and the controller adjusts the output peak power according to a detected linear velocity of the vehicle using an increasing function.
• According to a further aspect of the disclosed technique, there is thus provided an apparatus, for detecting at least one object, the apparatus being mounted on a vehicle, which includes a fiber laser, a motion detector, a scanner and a controller. The fiber laser is coupled with the motion detector and the scanner and the controller is coupled with the fiber laser and the motion detector. The fiber laser generates a beam of light, the motion detector detects the motion of the vehicle, the scanner directs the generated beam of light towards a volume of interest at a certain field-of-view (FOV) and the controller adjusts the FOV. The area the scanner can potentially direct the generated beam of light is referred to as a field-of-regard (FOR), the FOV refers to the area the scanner actually directs the generated beam of light for detecting the object, the FOV is smaller than the FOR and the controller adjusts the FOV according to the detected motion.
• According to another aspect of the disclosed technique, there is thus provided an apparatus, for detecting at least one object, the apparatus being mounted on a vehicle in motion, which includes a fiber laser, a motion detector, a scanner and a controller. The fiber laser is coupled with the motion detector and the scanner and controller is coupled with the fiber laser and the motion detector. The fiber laser generates a beam of light, the motion detector detects the motion of the vehicle, the scanner directs the generated beam of light towards a volume of interest at a certain line-of-sight (LOS) and the controller adjusts the LOS in the direction of the motion according to a detected angular velocity of the vehicle using an increasing function.
• According to a further aspect of the disclosed technique, there is thus provided an apparatus, for detecting at least one object, which includes a fiber laser, at least one receiver, a reflecting-transmitting plate and an optical assembly. The reflecting-transmitting plate is optically coupled with each receiver and the optical assembly is optically coupled with the fiber laser and with the reflecting-transmitting plate. The fiber laser generates at least one beam of light which is distinct compared to another beam of light, each receiver receives reflections of each beam of light from the object, the reflecting-transmitting plate reflects one of the beams of light towards one receiver and transmits another one of the beams of light towards another receiver and the optical assembly transmits and receives each beam of light. Each beam of light is transmitted at a different time.
• According to another aspect of the disclosed technique, there is thus provided an apparatus, for distinguishing between a pulsed light reflection from at least one object of interest and a pulsed light reflection from clutter, which includes a laser, at least one receiver, a pulse width detector and a processor. The pulse width detector is coupled with each receiver and the processor is coupled with the pulse width detector and with each receiver. The laser generates and transmits a pulsed beam of light, each receiver receives reflections of the pulsed beam of light from the object of interest and the clutter, the pulse width detector detects the pulse width of the pulsed light reflection and the processor distinguishes between the pulsed light reflection from the object of interest and the pulsed light reflection from the clutter. The processor provides an object of interest indication when the detected width of the pulsed light reflection is substantially similar to the pulse width of the transmitted pulsed beam of light and the processor provides a clutter indication when the detected width of the pulsed light reflection is substantially longer than the pulse width of the transmitted pulsed beam of light.
• According to a further aspect of the disclosed technique, there is thus provided a method, for detecting at least one object and preventing receiver burn-out, including the procedures of transmitting a low energy pulsed beam of light towards a volume of interest, detecting a reflection of the transmitted low energy pulsed beam of light from the object, in a predetermined time period and transmitting a high energy pulsed beam of light towards the volume of interest when the reflection of the transmitted low energy pulsed beam of light is not received within the predetermined time period.
• According to another aspect of the disclosed technique, there is thus provided a method, for detecting at least one object, including the procedures of scanning a volume of interest using a pulsed beam of light from a light source, from a moving vehicle, the pulsed beam of light being at a certain pulse repetition rate (PRR), detecting the motion of the vehicle and adjusting the PRR of the pulsed beam of light according to the detected motion.
• According to a further aspect of the disclosed technique, there is thus provided a method, for detecting at least one object, including the procedures of scanning a volume of interest using a pulsed beam of light from a light source, from a moving vehicle, the pulsed beam of light being at a certain output peak power, detecting the motion of the vehicle and adjusting the output peak power of the pulsed beam of light according to the detected motion.
• According to another aspect of the disclosed technique, there is thus provided a method, for detecting at least one object, including the procedures of scanning a volume of interest, from a moving vehicle, using a pulsed beam of light at a certain field-of-view (FOV), detecting the motion of the vehicle and adjusting the FOV according to detected motion of the vehicle.
• According to a further aspect of the disclosed technique, there is thus provided a method, for detecting at least one object, including the procedures of scanning a volume of interest, from a moving vehicle, using a pulsed beam of light at a certain line-of-sight (LOS), detecting the motion of the vehicle and adjusting the LOS in the direction of the motion according to a detected angular velocity of the vehicle using an increasing function.
BRIEF DESCRIPTION OF THE DRAWINGS
• The disclosed technique will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:
• FIG. 1A is a schematic illustration of a system, constructed and operative in accordance with an embodiment of the disclosed technique;
• FIG. 1B is a schematic illustration of the fiber laser ofFIG. 1A, constructed and operative in accordance with another embodiment of the disclosed technique;
• FIG. 1C is a schematic illustration of the fiber laser ofFIG. 1A, constructed and operative in accordance with a further embodiment of the disclosed technique;
• FIG. 2 is a schematic illustration of another fiber laser, constructed and operative in accordance with another embodiment of the disclosed technique;
• FIG. 3A is a schematic illustration of a system, constructed and operative in accordance with a further embodiment of the disclosed technique, used in the presence of an object having high reflectance;
• FIG. 3B is a schematic illustration of the system ofFIG. 3A, constructed and operative in accordance with another embodiment of the disclosed technique, used in the presence of an object having high reflectance;
• FIG. 3C is a schematic illustration of the system ofFIG. 3A, constructed and operative in accordance with a further embodiment of the disclosed technique, depicting a wire detection operation;
• FIG. 4 is a schematic illustration of a system, constructed and operative in accordance with another embodiment of the disclosed technique, depicting a floating output combiner;
• FIG. 5A is a schematic illustration of a system, constructed and operative in accordance with a further embodiment of the disclosed technique;
• FIG. 5B is a schematic illustration of a helicopter mounted with the system ofFIG. 5A, constructed and operative in accordance with another embodiment of the disclosed technique;
• FIG. 6A is a schematic illustration of changes to the PRR as a function of the linear motion of a vehicle mounted with the system ofFIG. 5A, constructed and operative in accordance with a further embodiment of the disclosed technique;
• FIG. 6B is another schematic illustration of changes to the PRR as a function of the angular motion of a vehicle mounted with the system ofFIG. 5A, constructed and operative in accordance with another embodiment of the disclosed technique;
• FIG. 7 is a schematic illustration of a system, constructed and operative in accordance with a further embodiment of the disclosed technique;
• FIG. 8A is a schematic illustration of a vehicle mounted with the system ofFIG. 7, constructed and operative in accordance with another embodiment of the disclosed technique, depicting the differences between the field-of-view and the field-of-regard of the vehicle;
• FIG. 8B is a schematic illustration of a vehicle mounted with the system ofFIG. 7, constructed and operative in accordance with a further embodiment of the disclosed technique;
• FIG. 8C is a schematic illustration of a vehicle mounted with the system ofFIG. 7, constructed and operative in accordance with another embodiment of the disclosed technique;
• FIG. 8D is a schematic illustration of a vehicle mounted with the system ofFIG. 7, constructed and operative in accordance with a further embodiment of the disclosed technique;
• FIG. 8E is a schematic illustration of a vehicle mounted with the system ofFIG. 7, constructed and operative in accordance with another embodiment of the disclosed technique;
• FIG. 8F is a schematic illustration of a vehicle mounted with the system ofFIG. 7, constructed and operative in accordance with a further embodiment of the disclosed technique;
• FIG. 8G is a schematic illustration of a vehicle mounted with the system ofFIG. 7, constructed and operative in accordance with another embodiment of the disclosed technique;
• FIG. 9 is a schematic illustration of a double LIDAR system, constructed and operative in accordance with a further embodiment of the disclosed technique;
• FIG. 10A is a schematic illustration of light beams reflecting off of different types of surfaces, constructed and operative in accordance with another embodiment of the disclosed technique;
• FIG. 10B is a schematic illustration of a system for distinguishing reflections from objects and from clutter, constructed and operative in accordance with a further embodiment of the disclosed technique;
• FIG. 11 is a schematic illustration of a system, constructed and operative in accordance with another embodiment of the disclosed technique;
• FIG. 12 is a schematic illustration of a method for wire detection, operative in accordance with a further embodiment of the disclosed technique;
• FIG. 13 is a schematic illustration of a method, operative in accordance with another embodiment of the disclosed technique; and
• FIG. 14 is a schematic illustration of a method, operative in accordance with a further embodiment of the disclosed technique.
DETAILED DESCRIPTION OF THE EMBODIMENTS
• The disclosed technique overcomes the disadvantages of the prior art by providing a novel laser obstacle ranging and display (herein abbreviated LORD) system and method. The LORD system includes a unique fiber laser capable of generating high energy laser beams, enabling the fiber laser to resolve hard-to-see obstacles, for example electrical wires, which may measure on the order of millimeters, from distances on the order of kilometers. The unique design of the fiber laser also increases the signal-to-noise (herein abbreviated S/N) ratio, thereby increasing the efficiency, and output capacity, of the fiber laser.
• The fiber laser is also unique in that the output combiner of the laser, where the laser beam is emitted from the fiber laser, does not require a delivery fiber to transmit the laser beam to an optical assembly for directing and focusing the laser beam on an obstacle. The output combiner can therefore be floated with respect to the “body” of the fiber laser. This feature increases the flexibility of design and reliability of the fiber laser, reduces energy loss in the emitted laser beam, and reduces the cost of the LORD system in general. It is noted that the fiber laser of the disclosed technique can be used with a fiber laser based LADAR (i.e., laser radar) system or a fiber based LIDAR (i.e., light imaging display and ranging) system. It is also noted that the LORD system of the disclosed technique can be classified as a LADAR system or a LIDAR system.
• It is noted that the use of the word “obstacle” in the description is used solely as an example. The disclosed technique described herein can be used to detect all types of objects, not just obstacles. Furthermore, the use of the words “laser beam” and “light beam” are used interchangeably. It is also noted that the disclosed technique herein described can be mounted on any kind of vehicle, for example, a helicopter, an airplane, a boat, a road vehicle and the like. Therefore the use of the word “pilot,” when describing the disclosed technique mounted on a vehicle, is meant to include all types of operators of vehicles.
• Furthermore, the disclosed technique can be used on autonomous and unmanned platforms, where a real operator is not physically located in the vehicle. Also, the term “hard-to-see,” or “hard to resolve,” with reference to objects or obstacles, referred to in the description below, refers to any object or obstacle which is several orders of magnitude smaller than the distance between the object and a LORD system. For example, telephone lines, which are on the order of centimeters, are hard-to-see obstacles from a helicopter located a few kilometers away from the telephone lines. It is further noted that the LORD system described herein can detect hard-to-see objects in a volume of interest, where the volume of interest can range from a few meters to a few kilometers, in general. It is also noted that the terms “fiber optic cable”, “optical fiber” and “fiber optics” are used interchangeably in the description and the claims, and that these terms refer to fiber optics and the cables used to transmit information from one point to another in the form of light.
• Reference is now made toFIG. 1A, which is a schematic illustration of a system, generally referenced50, constructed and operative in accordance with an embodiment of the disclosed technique.System50 is an example of a LORD system.System50 includes afiber laser52, areceiver54 and anindicator56.System50 also includes a scanner (not shown) and an image processing unit (not shown).
• Fiber laser52 is optically coupled withreceiver54.Receiver54 is coupled withindicator56.Receiver54 can be, for example, a sensor. It is noted thatfiber laser52 may be an eye-safe fiber laser, whereby the wavelength of the laser beam emitted fromfiber laser52 is a wavelength which is not damaging to the eye, for example between the range of 1.5 to 2.3 micrometers. It is also noted thatsystem50 may include a plurality of receivers.Indicator56 can be any device enabled to give information to a pilot, for example an audio system, a visual display system, an indicator lighting system, a tactile system, or a projection system for projecting information, or symbology (i.e. icons, directional arrows, aiming reticles, and the like), in the line-of-sight (herein abbreviated LOS) of the pilot.
• System50 is mounted on a vehicle (not shown).Fiber laser52 transmits light beams in front of the vehicle. The scanner scans a volume of interest (not shown) in which obstacles may be present by rastering the light beams transmitted byfiber laser52 over the volume of interest. Any obstacles in the volume of interest will cause some of the light beams, transmitted byfiber laser52, to reflect back tosystem50.Receiver54 receives the reflected light beams and detects the intensity of the reflected light beams. The detected intensity is then used byindicator56 to provide an indication of any obstacles present in the volume of interest.Indicator56 may issue an audio cue to a pilot, warning the pilot that an obstacle is in front of her, and instructing her how to avoid the obstacle.
• Indicator56 may also display an image of the volume of interest, the image being generated by the image processing unit, thereby allowing the pilot to see for herself how to best avoid the obstacles.Indicator56 may issue a tactile cue to the pilot, warning the pilot that an obstacle is in front of her. The image processing unit generates the image by processing the various intensities of all the reflected light beams.System50 can be used during daytime and nighttime conditions.
• In order forreceiver54 to receive reflections from hard-to-resolve objects, like antennas, electrical wires, telephones cables, and the like,fiber laser52 needs to emit narrow diameter light beams of high energy, where the output peak power offiber laser52 is on the order of tens of kilowatts. Such a high level of energy is required in order to resolve obstacles which may be on the order of millimeters from distances on the order of kilometers. The output peak power offiber laser52 is several orders of magnitude larger that the typical output peak power of fiber lasers, which are usually used in communication systems. In communication systems, the output peak power of fiber lasers is on the order of milliwatts.
• Reference is now made toFIG. 1B, which is a schematic illustration of the fiber laser ofFIG. 1A, generally referenced100, constructed and operative in accordance with another embodiment of the disclosed technique.Fiber laser100 includes asignal diode102, apreamplifier stage104 and abooster stage106.Fiber laser100 also includes thermoelectric coolers, a heat sink and an external forced air unit (none shown), for coolinglaser fiber100.
• Signal diode102 is optically coupled withpreamplifier stage104, andpreamplifier stage104 is optically coupled withbooster stage106. In general, all the components in a fiber laser are optically coupled by fiber optic cables.Signal diode102 can be a modulated distribution feedback (herein abbreviated DFB) single mode fiber-coupled laser diode. It is noted thatsignal diode102 can be set to work at operational wavelengths ranging from 1.5 to 2.3 micrometers. For example, signal diode can be set to work at operational wavelengths of 1.535 μm, 1.545 μm, 1.555 μm, 1.560 μm and 1.561 μm, which are all eye-safe wavelengths. In one embodiment of the disclosed technique, the operational wavelength is set to 1.561 μm. The use of eye-safe wavelengths infiber laser100 is significant in that it increases the applications whereinfiber laser100 can be used. For example iffiber laser100 is used in a LIDAR application (seeFIG. 11) then its operational wavelengths should be in the eye-safe range.Signal diode102 can generate pulsed beams of lights, with the pulse width of the output beam of light ranging from a few nanoseconds to thousands of nanoseconds, for example from 3 nanoseconds to 2000 nanoseconds. It is noted that the bandwidth ofsignal diode102 is narrow as compared to the bandwidth of the doped fiber amplifier used inpreamplifier stage104.
• The pulse width of the output beam of light can be adjusted via an interface (not shown) tofiber laser100. The frequency at whichsignal diode102 generates pulsed beams of light is generally on the order of tens to hundreds, or thousands, of kilohertz, for example from one kilohertz to one thousand kilohertz. It is noted that this frequency is several orders of magnitude smaller that the frequency used by fiber lasers in communication systems. It is also noted that the shape and width of the pulsed beams of light generated bysignal diode102 remain substantially constant whilefiber laser100 is in use.
• In general,signal diode102 generates a low energy beam of light, on the order of tens of microwatts.Preamplifier stage104 then amplifies the low energy beam of light twice, and sends the double amplified beam of light tobooster stage106.Booster stage106 further amplifies the double amplified beam of light and outputs the beam of light towards an optical assembly (not shown) which directs and focuses the beam of light towards a volume of interest. It is noted thatfiber laser100 is constructed using a master oscillator power amplifier (herein abbreviated MOPA) approach.
• Preamplifier stage104 includes acirculator108, an erbium doped fiber (herein abbreviated EDF)110, a wavelength division multiplexer (herein abbreviated WDM)112, a narrowband Bragg reflector114, afiber pump diode116, aband pass filter118,fiber optic cables130₁and130₂.Preamplifier stage104 also includes a delay line (not shown), betweenWDM112 and narrowband Bragg reflector114.Circulator108 is optically coupled withsignal diode102,EDF110 andband pass filter118.EDF110 is optically coupled withWDM112.WDM112 is optically coupled with both narrowband Bragg reflector114 andfiber pump diode116. The delay line is optically coupled with bothWDM112 and narrowband Bragg reflector114.Fiber optic cable130₁optically couplesEDF110 tocirculator108 andWDM112.Fiber optic cable130₂optically couplesfiber pump diode116 toWDM112. In general, as mentioned above, all the components infiber laser100 are optically coupled by fiber optic cables, although in particular, an EDF and a fiber pump diode are optically coupled within a fiber laser via fiber optic cables. It is noted thatEDF110 can be substituted by an erbium-ytterbium co-doped fiber. It is also noted thatEDF110 is a single mode fiber amplifier.
• Fiber pump diode116 can be a fiber coupled DFB laser diode. Narrowband Bragg reflector114 can also be a fiber Bragg grating (not shown). It is noted thatband pass filter118 is an optional component. It is furthermore noted thatsignal diode102 andfiber pump diode116 are located on opposite sides ofEDF110, which was found to increase the S/N ratio, thereby increasing the efficiency ofpreamplifier stage104. In fiber amplifiers used in communication systems, the signal diode and the fiber pump diode are usually located on the same side of the EDF. It is also noted that in fiber amplifiers used in communication systems, a wide band Bragg reflector is used, unlike in the disclosed technique. It is furthermore noted that the bandwidth ofEDF110 is by the specification of erbium doped fibers wide as compared with the bandwidth ofsignal diode102 and narrowband Bragg reflector114.
• Circulator108 receives the low energy beam of light generated bysignal diode102.Circulator108 then directs the low energy beam of light, viafiber optic cable130₁towardsEDF110.EDF110 amplifies the low energy beam of light. This amplification is achieved by usingfiber pump diode116, which pumpsEDF110 viaWDM112.Fiber pump diode116 generates a beam of light, for pumpingEDF110, on the order of hundreds of milliwatts, for example a beam of light having an energy ranging from 100 to 500 milliwatts. The operational wavelength of the beam of light generated byfiber pump diode116 may be on the order of hundreds of nanometers, for example 920 nm, 940 nm, 960 nm or 980 nm. In general, the operational wavelength offiber pump diode116 ranges from 910 nm to 985 nm. In one embodiment of the disclosed technique, the operational wavelength offiber pump diode116 ranges from either 915 nm to 930 nm or 940 nm to 960 nm. These ranges possess wide absorption spectra. It is noted that the length ofEDF110 is suited to match the characteristic absorption length of such fibers. A change or increase in the length ofEDF110 from the characteristic absorption length of erbium doped fibers by a factor as small as 2 may prevent or stopEDF110 from amplifying the low energy beam of light.
• WDM112 allowsEDF110 to receive the beam of light generated fromfiber pump diode116 without interference from the low energy beam of light being amplified byEDF110.WDM112 provides the amplified beam of light to narrowband Bragg reflector114, which reflects the amplified beam of light back toWDM112, which in turn, reflects the amplified beam of light back through EDF110 a second time. Narrowband Bragg reflector114 ensures that only the amplified beam of light generated bysignal diode102 is reflected back throughEDF110 and none of the beam of light generated byfiber pump diode116.Circulator108 directs the double amplified beam of light towardsband pass filter118.Band pass filter118 only allows the beam of light emitted fromsignal diode102 to pass there through. Since the beam of light amplified byEDF110 can destroy the beam of light generated bysignal diode102,band pass filter118, as well as narrowband Bragg reflector114, are included inpreamplifier stage104 to suppress any spontaneous light emissions that may result fromEDF110. The bandwidth ofsignal diode102 and narrowband Bragg reflector114 are selected to be substantially similar to enable narrowband Bragg reflector114 to only reflect narrow band energy which originated fromsignal diode102 and not wide band energy originating fromEDF110.
• The use of the delay line betweenWDM112 and narrowband Bragg reflector114 ensures that the pulse width of the amplified beam of light is not significantly reduced after it is reflected back toWDM112 by narrowband Bragg reflector114. It was found that without the use of the delay line, the pulse width of the amplified beam of light was significantly reduced. Such a reduction in pulse width can significantly increase the output peak power of the amplified beam of light, thereby causing damage to the elements inpreamplifier stage104 as the amplified beam of light is reflected back toWDM112 and provided toEDF110. Since light is traveling throughEDF110 in two directions, numerous unwanted effects can occur inpreamplifier stage104 because of the interference between the low energy beam of light provided bysignal diode102 tocirculator108 toEDF110 and the amplified beam of light provided byWDM112 back toEDF110. Such effects can include energy remaining inEDF110, standing waves being formed inEDF110, hole burning in the optical fibers which couple the various components ofpreamplifier stage104 and non-homogenous energy extraction fromEDF110, each of which cause energy fluctuations inpreamplifier stage104. The use of the delay line inpreamplifier stage104 prevents the above mentioned unwanted effects from occurring inpreamplifier stage104. The delay line enables the amplified beam of light to maintain a stabilized pulse shape. The delay of the delay line provides a delay time equal to or greater than the pulse width of the low energy beam of light provided bysignal diode102. By using the delay line, the amplified beam of light maintains its initial pulse width and stability, is amplified significantly without change to its peak power and damage to the components ofpreamplifier stage104 is avoided. The delay line prevents interference from occurring inpreamplifier stage104.
• Booster stage106 includes aninput combiner120, afiber pump diode122, an erbium-ytterbium co-doped fiber (herein abbreviated EYDF)124, anoutput combiner126, afiber pump diode128 andfiber optic cables130₃,130₄and130₅. It is noted thatinput combiner120 can be substituted for a double clad WDM.Booster stage106 also includes band pass filters (not shown), optically coupled withinput combiner120 and withoutput combiner126, for preventingfiber pump diodes122 and128 from being destroyed by the amplified beam of light.Input combiner120 is optically coupled withpump diode122,EYDF124 andband pass filter118.EYDF124 is optically coupled withoutput combiner126.Pump diode128 is optically coupled withoutput combiner126.Fiber optic cable130₃optically couplesfiber pump diode122 to inputcombiner120.Fiber optic cable130₄optically couplesinput combiner120 withoutput combiner126.Fiber optic cable130₅optically couplesfiber pump diode128 withoutput combiner126. In general, as mentioned above, all the components infiber laser100 are coupled by fiber optic cables, although in particular, an EYDF and fiber pump diodes are optically coupled within a fiber laser via fiber optic cables. It is noted that the choice of an EYDF forbooster stage106 is significant erbium-ytterbium co-doped fibers absorb and transfer energy differently than erbium doped fibers or ytterbium doped fibers. Whereas both erbium doped fibers and ytterbium doped fibers can be pumped directly, erbium-ytterbium co-doped fibers are pumped indirectly. In erbium-ytterbium co-doped fibers, ytterbium ions absorb energy and transfer that energy to erbium ions. The erbium ions will then only begin to become excited and emit laser radiation when a threshold amount of energy has been absorbed by the ytterbium ions and transferred to them. The indirect pumping of erbium-ytterbium co-doped fibers enablesbooster stage106 to amplify the double amplified beam of light a third time without damage to the components ofbooster stage106 by limiting the amount of energy amplified inEYDF124 by way of the threshold amount of energy erbium ions require to amplify energy.
• Fiber pump diodes122 and128 can each be low cost fiber coupled laser diodes.EYDF124 includes a double clad erbium-ytterbium fiber that can be pumped from both ends.EYDF124 is a multimode fiber amplifier. It is noted thatEDF110, which as is a single mode fiber amplifier, transfers the amplified beam of light toEYDF124 which is a multimode fiber amplifier. By transferring energy inpreamplifier stage104 from a single mode to a multimode inbooster stage106, energy transfer frompreamplifier stage104 tobooster stage106 is maintained at an efficient level and the occurrence of light energy inbooster stage106 traveling back intopreamplifier stage104 is prevented.Fiber pump diodes122 and128 each generate a beam of light, for pumpingEYDF124, on the order of tens of watts, for example a beam of light having an energy ranging up to 30 watts. The operational wavelength of the beam of light generated byfiber pump diodes122 and128 may be on the order of hundreds of nanometers, for example 920 nm, 940 nm, 960 nm or 980 nm. In general, the operational wavelengths offiber pump diodes122 and128 range from 910 nm to 985 nm. In one embodiment of the disclosed technique, the operational wavelengths offiber pump diodes122 and128 range from either 915 nm to 930 nm or 940 nm to 960 nm. These ranges possess wide absorption spectra.Input combiner120 andoutput combiner126 each include collimating and focusing lenses, dichroic mirrors and protective filters (none shown). The collimating and focusing lenses are used for properly focusing and directing the output beam of light. The dichroic mirrors are used for combining the beam of light with beams of light generated byfiber pump diodes122 and128. The protective filters are for protectingfiber pump diodes122 and128 from laser light damage. It is noted that in general the length ofEYDF124 is suited to match the characteristic absorption length of such fibers. A change or increase in the length ofEYDF124 from the characteristic absorption length of erbium-ytterbium co-doped fibers by a factor as small as 2 may prevent or stopEYDF124 from amplifying the double amplified beam of light. SinceEYDF124 is pumped from both ends, the length ofEYDF124 is selected to be double the characteristic absorption length of an erbium-ytterbium co-doped fiber, as each offiber pump diodes122 and128 pumps one characteristic absorption length ofEYDF124. By doubling the length ofEYDF124, spontaneous emissions fromEYDF124 can be reabsorbed, heat removal fromEYDF124 is enhanced without the use of additional elements and the output power and energy of the doubly amplified beam of light which entersEYDF124 is doubled as it is amplified a third time. Since EYDF is pumped from both ends, the energy, gain and temperature ofEYDF124 is homogenous over the length ofEYDF124. By maintaining a homogenous energy, gain and temperature over the length ofEYDF124, hole burning of the optical fibers ofEYDF124 is prevented.
• Band pass filter118 provides the double amplified beam of light to inputcombiner120.Input combiner120 provides the double amplified beam of light toEYDF124, which will amplify the already double amplified beam of light a third time. This amplification is achieved by usingfiber pump diodes122 and128, which pumpEYDF124 from both ends.Input combiner120 andoutput combiner126 each allow the beams of light produced byfiber pump diodes122 and128 to be combined with the double amplified beam of light such that it can be amplified a third time. It is noted that inbooster stage106, the double amplified beam of light is passed throughEYDF124 only once.Output combiner126 output the triple amplified beam of light to an optical assembly (not shown), which transmits the beam of light towards a volume of interest. The average output power (i.e., amount of power per second) of the output beam of light, after being amplified thrice, can range from 5 to 10 watts, and the output peak power, of the output beam of light, can range from 100 watts to 100 kilowatts.
• It is noted that additional pre-amplification stages (not shown) can be placed betweenpreamplifier stage104 andbooster stage106. In such an embodiment, each additional pre-amplification stage would include a circulator, an EDF, a WDM, a narrow band reflector and a pump diode. The circulator would be coupled with one end of the EDF, while the WDM would be coupled with the other end of the EDF. The pump diode would be coupled with the WDM. The narrow band reflector would be coupled with the WDM. Each additional preamplifier stage would be coupled by way of the respective circulator. The first additional preamplifier stage would be coupled withband pass filter118 inpreamplifier stage104 by way of its circulator. The last additional preamplifier stage would be coupled withinput combiner120 inbooster stage106 by way of its circulator. Additional preamplifier stages would be coupled to one another by way of their respective circulators. In this embodiment, each additional preamplifier stage would provide a double pass amplification. In another embodiment of the additional preamplifier stages, each preamplifier stage would include a circulator, an EDF, two WDMs and two pump diodes. Each pump diode would be coupled with a WDM, with one WDM coupled to one side of the EDF and the other WDM coupled to the other side of the EDF. One of the WDM's would be coupled with the circulator. As mentioned above, additional preamplifier stages would be coupled to one another by way of their respective circulators. The first additional preamplifier stage would be coupled withband pass filter118 inpreamplifier stage104 by way of its circulator. The last additional preamplifier stage would be coupled withinput combiner120 inbooster stage106 by way of its circulator. In a further embodiment of the additional preamplifier stages, each preamplifier stage would include an EDF, a WDM and a pump diode. The EDF would be coupled with the WDM. The pump diode would be coupled with the WDM. In this embodiment, each additional preamplifier stage would provide a single pass amplification. Each additional preamplifier stage would be coupled by way of its respective EDF and WDM. The first additional preamplifier stage would be coupled withband pass filter118 inpreamplifier stage104 by way of its EDF. The last additional preamplifier stage would be coupled withinput combiner120 inbooster stage106 by way of its WDM. Additional preamplifier stages would be coupled to one another by way of their respective EDF and WDM. The WDM of a first additional preamplifier stage would be coupled to the EDF of a second additional preamplifier stage.
• Reference is now made toFIG. 1C, which is a schematic illustration of the fiber laser ofFIG. 1A, generally referenced132, constructed and operative in accordance with a further embodiment of the disclosed technique.Fiber laser132 includes asignal diode134, apreamplifier stage136, asplitter138 and booster stages140₁,140₂,140₃and140_N.Signal diode134 is coupled withpreamplifier stage136, which is in turn coupled withsplitter138.Splitter138 is coupled with each of booster stages140₁,140₂,140₃and140_N.Signal diode134 is substantially similar to signal diode102 (FIG. 1B).Preamplifier stage136 is substantially similar to preamplifier stage104 (FIG. 1B) in terms of its components. Each of booster stages140₁,140₂,140₃and140_Nis similar to booster stage106 (FIG. 1B) in terms of its components.Splitter138 can be a fiber splitter or a 1×N coupler.
• Signal diode134 generates a low energy beam of light, on the order of tens of microwatts.Preamplifier stage136 then amplifies the low energy beam of light twice, and sends the double amplified beam of light tosplitter138.Splitter138 splits the double amplified beam of light into N double amplified beams of light, providing each split double amplified beam of light to one of booster stages140₁,140₂,140₃and140_N. Each of booster stages140₁,140₂,140₃and140_Nfurther amplifies its respective double amplified beam of light and outputs the beam of light towards a respective optical assembly (not shown) which directs and focuses each respective beam of light towards a volume of interest. The beams of light outputted by each respective optical assembly can be directed towards different segments of a volume of interest, thereby increasing the size of the volume of interest which can be scanned and searched. The beams of light outputted by each respective optical assembly can also be directed towards similar segments of a volume of interest, thereby overlapping and increasing the amount of output power used to scan and search the volume of interest.
• Reference is now made toFIG. 2, which is a schematic illustration of another fiber laser, generally referenced150, constructed and operative in accordance with a further embodiment of the disclosed technique.Fiber laser150 includes apreamplifier stage152, abooster stage154, two signal diodes156₁and156₂, acommutator158 and a power supplysignal diode driver160. In an embodiment of the disclosed technique,fiber laser150 includes a plurality of signal diodes, each optically coupled withpreamplifier stage152 andcommutator158.Booster stage154 includes an output combiner and a fiber pump diode (both not shown), for transmitting the output beam of light. It is noted thatbooster stage154 is an optional component. In an embodiment of the disclosed technique wherebooster stage154 is not included,preamplifier stage152 includes the output combiner and the fiber pump diode (both not shown), for transmitting the output beam of light.Preamplifier stage152 can be constructed like preamplifier stage104 (FIG. 1B).
• Booster stage154 can be constructed like booster stage106 (FIG. 1B).Preamplifier stage152 is optically coupled withbooster stage154. Signal diodes156₁and156₂are each optically coupled withpreamplifier stage152.Commutator158 is coupled with each of signal diodes156₁and156₂. Power supplysignal diode driver160 is coupled withcommutator158.
• Signal diodes156₁and156₂each generate a distinct pulsed beam of light. In one embodiment of the disclosed technique, the pulsed beams of light generated by signal diodes156₁and156₂have the same wavelength, pulse width and pulse frequency (the pulse frequency being the frequency at which the pulsed beam of light is transmitted), being separated in time. In this embodiment, the pulsed beams of light generated by each of signal diodes156₁and156₂are provided topreamplifier stage152 at different times. The time difference between when the pulsed beams of light are each provided topreamplifier stage152 can range between ten to hundreds of microseconds. In general, the time difference is related to the time it takes a vehicle, mounted with a fiber laser likefiber laser150, to change its LOS, which can take anywhere from a few milliseconds to hundreds of milliseconds.
• In another embodiment of the disclosed technique, the pulsed beams of light generated by signal diodes156₁and156₂are distinct only in wavelength, with signal diode156₁generating a pulsed beam of light at wavelength λ₁, and signal diode156₂generating a pulsed beam of light at wavelength λ₂. In a further embodiment of the disclosed technique, the pulsed beams of light generated by signal diodes156₁and156₂are distinct only in pulse width, with each of signal diodes156₁and156₂generating pulsed beams of light with different pulse widths. In another embodiment of the disclosed technique, one of the signal diodes generates a pulsed beam of light which is a single frequency beam of light, while the other signal diode generates a pulsed beam of light which is a multi-frequency beam of light. A single frequency beam of light refers to a beam of light having a single longitudinal mode, whereas a multi-frequency beam of light refers to a beam of light with multiple modes.
• It is noted that in this embodiment of the disclosed technique, a single frequency fiber laser or a solid state laser can be substituted for the signal diode generating the single frequency beam of light. Furthermore, a fiber laser oscillator or a solid state laser oscillator, such as a microchip laser, can be substituted for the signal diode generating the multi-frequency beam of light. In a further embodiment of the disclosed technique, the pulsed beams of light generated by signal diodes156₁and156₂are distinct only in amplitude, with each of signal diodes156₁and156₂generating pulsed beam of light with different amplitudes. In another embodiment of the disclosed technique, the pulsed beams of light generated by signal diodes156₁and156₂are distinct only in types of polarization, with each of signal diodes156₁and156₂generating pulsed beam of light with a different type of polarization.
• It is noted that the different types of polarizations can include linear and circular polarizations, as well as different specific configurations of polarization. In each of the above mentioned embodiments regarding the distinct nature of each of pulsed beams of light, one pulsed beam of light can be significantly lower in output peak power than the other pulsed beam of light. For example, the pulsed beam of light generated by signal diode156₁may be 30 to 40 dB weaker than the pulsed beam of light generated by signal diode156₂. Furthermore, as explained below, in some of the above mentioned embodiments regarding the distinct nature of each of the pulsed beams of light, the two pulsed beams of light are always separated in time and are therefore not transmitted simultaneously.
• The pulsed beams of light generated by signal diodes156₁and156₂are each provided, in turn, topreamplifier stage152, which amplifies each of the pulsed beams of light twice. The amplified pulsed beams of light are then provided tobooster stage154, which further amplifies the pulsed beams of light.Booster stage154 then outputs the amplified pulsed beams of light. In the embodiment wherebooster stage154 is not included,preamplifier stage152 outputs the amplified pulsed beams of light.
• In theory, if more than one signal diode were to be used in a fiber laser, where each signal diode generates pulsed beams of light which differ significantly in output peak power, then each signal diode would need to have its own power supply signal diode driver. Each power supply signal diode driver would then be used for providing the specific amount of energy to a single signal diode to generate a pulsed beam of light at a particular energy level. In the disclosed technique, only power supplysignal diode driver160, which is a single power supply signal diode driver, is used to supply specific amounts of energy to each of signal diodes156₁and156₂. In the disclosed technique,commutator158 allows each of signal diodes156₁and156₂to draw a particular amount of energy from power supplysignal diode driver160. As such, signal diodes156₁and156₂can each generate pulsed beams of light at significantly different levels of energy, using only a single power supply signal diode driver.
• It is noted thatcommutator158 can only provide a particular energy level from power supplysignal diode driver160 to a single signal diode at a particular moment in time. Therefore, the pulsed beams of light generated by signal diodes156₁and156₂will be separated in time. In a further embodiment of the disclosed technique, the pulsed beams of light generated by signal diodes156₁and156₂are generated simultaneously. In this embodiment, the output peak power of the pulsed beams of light generated by each of the signal diodes can differ if each signal diode has a different output peak power. Therefore, even thoughcommutator158 will simultaneously provide each of signal diodes156₁and156₂with the same amount of energy, signal diodes156₁and156₂can each generate a pulsed beam of light having a distinct output peak power. It is noted that in general,commutator158 is operative at a duty cycle on the order of microseconds.
• Therefore, spacing between pulsed beams of light generated by signal diodes156₁and156₂will be on the order of microseconds. It is further noted that in general, the pulse width of the pulsed beams of light generated by signal diodes156₁and156₂is on the order of nanoseconds, ranging from a few nanoseconds to thousands of nanoseconds.
• As mentioned above with reference toFIG. 1A, in order for a receiver to receive reflections from hard-to-resolve objects, like antennas, electrical wires, telephones cables, and the like, a fiber laser needs to emit narrow diameter light beams of high energy, where the output peak power of the fiber laser is on the order of tens of kilowatts. Such a high level of energy is required in order to resolve obstacles which may be on the order of millimeters from distances on the order of kilometers. If such a high level of energy were to reflect from an object having a surface of high reflectance, such as a retro-reflector, which is any object that can reflect a beam of light directly back towards a receiver at substantially the same energy level the beam of light was originally transmitted at, the receiver would most certainly burn-out from the large amount of energy impinging upon its surface.
• For example, if the output peak power of a beam of light emerging from the fiber laser is 10 kilowatts, then the output peak power of the reflected beam of light, reflected from a retro-reflector, could be 1 to 10,000 watts. This amount of very high energy could easily burn-out a receiver, thereby rendering system50 (FIG. 1A) not operational. In order to protect the receiver insystem50 from burning out, a fiber laser, constructed likefiber laser150, is used insystem50, as described with reference toFIGS. 3A,3B and3C. It is noted that the fiber laser used insystem50, as described with reference toFIGS. 3A,3B and3C, in one embodiment, can be replaced by a solid state laser, and in another embodiment, can be replaced by a semiconductor laser configured in a master oscillator power amplifier approach.
• Reference is now made toFIG. 3A, which is a schematic illustration of a system generally referenced180, constructed and operative in accordance with a further embodiment of the disclosed technique, depicting howsystem180 operates in the presence of an object having high reflectance. In the presence of such an object,system180 may enter a situation of receiver burn-out.System180 includes afiber laser182 and areceiver184.Fiber laser182 is constructed and operative in a manner similar to fiber laser150 (FIG. 2).Receiver184 is constructed and operative to receive reflections of pulsed beams of light emitted fromfiber laser182 which are reflected from objects in a volume of interest in front ofsystem180.Fiber laser182 can send out two different pulsed beams of light, one with a high level of energy and one with a low level of energy.
• FIG. 3A shows howreceiver184 can burn-out if a high level pulsed beam of light is used to detect objects in the volume of interest in front ofsystem180.Fiber laser182 generates a high energy pulsed beam of light186 (thick arrows), in order to detect hard-to-see objects in the volume of interest ofsystem180. Instead of impinging upon a hard-to-see object, high energy pulsed beam oflight186 impinges upon anobject190 having a surface of high reflectance. For example, object190 could be a retro-reflector, like a stop sign, whose surface is coated with retro-reflective materials. Because of its ability to reflect light beams impinging upon its surface at substantially the same energy level the light beams were originally transmitted at,object190 reflects high energy pulsed beam oflight186 as a high energy pulsed beam of light188 (thick arrows), with almost no loss in the energy level of high energy pulsed beam oflight188 as compared with the energy level of high energy pulsed beam oflight186. High energy pulsed beam oflight188 can be on the order of hundreds or thousands of watts.
• If high energy pulsed beam oflight188 impinges uponreceiver184, thenreceiver184 will burn-out. Therefore, if high energy pulsed beam oflight186 is used to detect hard-to-see objects, thensystem180 runs the risk of burning outreceiver184 if an object having high reflectance is located in the volume of interest in front ofsystem180.
• Reference is now made toFIG. 3B, which is a schematic illustration of the system ofFIG. 3A, generally referenced200, constructed and operative in accordance with another embodiment of the disclosed technique, depicting howsystem200 operates in the presence of an object having high reflectance.System200 includes afiber laser202 and areceiver204.Fiber laser202 is constructed and operative in a manner similar to fiber laser150 (FIG. 2).Receiver204 is constructed and operative to receive reflections of pulsed beams of light emitted fromfiber laser202 which are reflected from objects in a volume of interest in front ofsystem200.Fiber laser202 can send out two different pulsed beams of light, one with a high level of energy and one with a low level of energy.
• FIG. 3B shows howreceiver204 can be protected from burn-out if a low level pulsed beam of light is used to detect objects in the volume of interest in front ofsystem200.Fiber laser202 generates a low energy pulsed beam of light206 (thin arrows), in order to detect hard-to-see objects in the volume of interest ofsystem200. Instead of impinging upon a hard-to-see object, low energy pulsed beam oflight206 impinges upon anobject210 having a surface of high reflectance. For example, object210 could be a retro-reflector such as a stop sign whose surface is coated with retro-reflective materials. Because of its ability to reflect light beams impinging upon its surface at substantially the same energy level the light beams were originally transmitted at,object210 reflects low energy pulsed beam oflight206 as a low energy pulsed beam of light208 (thin arrows). Low energy pulsed beam oflight208 has enough energy to reflect all the way back toreceiver204.
• Since low energy pulsed beam oflight202 has a low output peak power, low energy pulsed beam oflight208 will not be powerful enough to burn-out receiver204, andreceiver204 can detect and receive low energy pulsed beam oflight208. Therefore, if low energy pulsed beam oflight206 is used to detect hard-to-see objects,system200 will never run the risk of burning outreceiver204 if an object of high reflectance is located in the volume of interest in front ofsystem200. On the other hand, if no objects having high reflectance are located in the volume of interest in front ofsystem200, then low energy pulsed beam oflight206 will not be reflected back towardsreceiver204, as any reflections from hard-to-see objects from low energy pulsed beam oflight206 will dissipate before reachingreceiver204. This is explained in further detail with reference toFIG. 3C.
• Reference is now made toFIG. 3C, which is a schematic illustration of a system, generally referenced240, constructed and operative in accordance with a further embodiment of the disclosed technique, which depicts a wire detection operation.FIG. 3C also depicts how receiver burn-out is avoided and prevented insystem240.System240 includes afiber laser242 and areceiver244.Fiber laser242 is constructed and operative in a manner similar to fiber laser150 (FIG. 2).Receiver244 is constructed and operative to receive reflections of pulsed beams of light emitted fromfiber laser242 which are reflected from objects in a volume of interest in front ofsystem240.Fiber laser242 can send out two different pulsed beams of light, a low energy pulsed beam of light246 (thin arrows) and a high energy pulsed beam of light248 (thick arrows). Low energy pulsed beam oflight246 and high energy pulsed beam oflight248 are sent towardspower lines252, which are suspended betweenposts250.
• In order to prevent the burn-out ofreceiver244,system240 first transmits low energy pulsed beam oflight246, and waits to see ifreceiver244 receives a reflection from objects in the volume of interest in front ofsystem240. When low energy pulsed beam oflight246 is reflected frompower lines252, a pulsed beam of light254 (dotted arrows) is reflected back towardsreceiver244. Sincepower lines252 are very thin and are not highly reflective objects, pulsed beam oflight254 is significantly lower in energy than low energy pulsed beam oflight246. In fact, pulsed beam oflight254 is so low in energy that it dissipates before it is received byreceiver244.
• After a waiting period, ranging from a few microseconds to hundreds of microseconds, ifreceiver244 does not receive pulsed beam of light254 (which it will not, from hard-to-see objects), or if the energy level of a reflected pulsed beam of light does not exceed a predetermined threshold, thenfiber laser242 sends out high energy pulsed beam oflight248. When high energy pulsed beam oflight248 is reflected frompower lines252, a pulsed beam of light256 (thin arrows) is reflected back towardsreceiver244. Sincepower lines252 are very thin and are not highly reflective objects, pulsed beam oflight256 is significantly lower in energy than high energy pulsed beam oflight248. The energy level of pulsed beam oflight256 is high enough such thatreceiver244 will be able to receive and detect it.
• Sincereceiver244 did not receive pulsed beam oflight254,system240 operates under the assumption that no objects having high reflectance are located in its volume of interest. Therefore,fiber laser242 can safely transmit high energy pulsed beam oflight248 in order to detect hard-to-see objects, with no risk of self burn-out. If an object having high reflectance is located in the volume of interest in front ofsystem240, thenreceiver244 will receive a reflected pulsed beam of light of low energy pulsed beam oflight246. If an object having high reflectance is located beyond the volume of interest in front ofsystem240, thenreceiver244 will also receive a reflected pulsed beam of light of low energy, as reflections coming from such a distance will impinge uponreceiver244 as low energy beams of light. The energy of low energy pulsed beam oflight246 is such that it will not cause the burn-out ofreceiver244.System240 will then not transmit high energy pulsed beam oflight248.
• When the LOS ofsystem240 changes,system240 will again first transmit low energy pulsed beam oflight246, and wait to see ifreceiver244 receives a reflection from objects in the volume of interest in front ofsystem240, before transmitting high energy pulsed beam oflight248. Changes in the LOS ofsystem240 can be determined by a motion detector (not shown), coupled withsystem240.System240 therefore preventsreceiver244 from burning out, by determining the power ratio between a transmitted beam of light and its respectively detected reflected beam of light. The power ratio is defined as the intensity of the detected reflected beam of light to the intensity of the transmitted beam of light. This power ratio will be essentially the same for high energy as well as low energy beams of light. When the laser beam is reflected from objects having high reflectance or close proximity low absorption objects, this ratio is significantly high which means that a reflected high power laser beam might cause receiver burn-out. Accordingly, the system further determines a receiver burn-out threshold, under which it is safe to transmit high power laser beams.
• It is also noted that, in general, the volume of interest is defined as a volume beyond which even high energy pulsed beams of light reflecting from objects having high reflectance will impinge uponreceiver244 as low energy pulsed beams of light. Therefore, if a high energy pulsed beam of light is transmitted and no objects having high reflectance are located in the volume of interest, but objects having high reflectance are located beyond the volume of interest, then even if the high energy pulsed beam of light reflects from such an object, receiver burn-out will be prevented, as the received reflected pulsed beam of light will be of low energy.
• Sincesystem240 transmits a low energy beam of light first, if the power ratio exceeds the receiver burn-out threshold (e.g., the power ratio is close to one, which resulted when the low energy beam of light most probably reflected from an object having high reflectance), thensystem240 will not transmit the high energy beam and the next transmitted laser beam shall be a low energy one. Accordingly,system240 transmits low power beams of light until the power ratio is lower than the receiver burn-out threshold (e.g., when an object having high reflectance is not present in the LOS ofsystem240, either by changing the LOS of the system or the object moved away from the current LOS). If the power ratio does not exceed the receiver burn-out threshold thensystem240 will transmit the high energy beam of light, in the same direction the low energy beam of light was transmitted, in order to detect hard-to-see objects and obstacles located in the volume of interest ofsystem240.
• Reference is now made toFIG. 4, which is a schematic illustration of a system, generally referenced280, constructed and operative in accordance with another embodiment of the disclosed technique.System280 depicts a floating output combiner.System280 includes afiber laser282, anoutput combiner310, aninterface312 and anoptical assembly314.Fiber laser282 is optically coupled withoutput combiner310.Output combiner310 is optically coupled withinterface312.Interface312 is coupled withoptical assembly314.Interface312 can be an opto-mechanical interface. It is noted thatoutput combiner310 is not necessarily physically attached tofiber laser282.
• Fiber laser282 includes asignal diode284, apreamplifier stage286 and abooster stage288.Signal diode284 is optically coupled withpreamplifier stage286, andpreamplifier stage286 is optically coupled withbooster stage288. In general, all the components in a fiber laser are optically coupled by fiber optic cables. It is noted that all the components offiber laser282 are similar to like components found in fiber laser100 (FIG. 1B). It is also noted thatbooster stage288 is an optional component. In general,signal diode284 generates a low energy beam of light, on the order of tens of microwatts.Preamplifier stage286 then amplifies the low energy beam of light twice, and sends the double amplified beam of light tobooster stage288.Booster stage288 further amplifies the double amplified beam of light and outputs the beam of light towardsoptical assembly314 which directs and focuses the beam of light towards a volume of interest.
• Preamplifier stage286 includes acirculator290, anEDF292, aWDM294, a narrowband Bragg reflector296, afiber pump diode298, aband pass filter300 andfiber optic cables309₁and309₂.Circulator290 is optically coupled withsignal diode284,EDF292 and withband pass filter300.EDF292 is optically coupled withWDM294.WDM294 is optically coupled with both narrowband Bragg reflector296 and withfiber pump diode298.Fiber optic cable309₁optically couplesEDF292 tocirculator290 andWDM294.Fiber optic cable309₂optically couplesfiber pump diode298 toWDM294. In general, as mentioned above, all the components infiber laser282 are optically coupled by fiber optic cables, although in particular, an EDF and a fiber pump diode are optically coupled within a fiber laser via fiber optic cables. It is noted thatband pass filter300 is an optional component.
• Circulator290 receives the low energy beam of light generated bysignal diode284.Circulator290 then directs the low energy beam of light, viafiber optic cable309₁towardsEDF292.EDF292 amplifies the low energy beam of light. This amplification is achieved by usingfiber pump diode298, which pumpsEDF298 viaWDM294.Fiber pump diode298 generates a beam of light, for pumpingEDF292, on the order of hundreds of milliwatts.WDM294 allowsEDF292 to receive the beam of light generated fromfiber pump diode298 without interference from the low energy beam of light being amplified byEDF292.WDM294 provides the amplified beam of light to narrowband Bragg reflector296, which reflects the amplified beam of light back toWDM294, which in turn, reflects the amplified beam of light back through EDF292 a second time. Narrowband Bragg reflector296 ensures that only the amplified beam of light generated bysignal diode284 is reflected back throughEDF292 and none of the beam of light generated byfiber pump diode298.
• Circulator290 directs the double amplified beam of light towardsband pass filter300.Band pass filter300 only allows the beam of light emitted fromsignal diode284 to pass there through.
• Booster stage288 includes aninput combiner302, afiber pump diode304, anEYDF306, afiber pump diode308 andfiber optic cables309₃,309₄and309₅.Input combiner302 is optically coupled withpump diode304,EYDF306 and withband pass filter300.Fiber optic cable309₃optically couplesfiber pump diode304 to inputcombiner302. In general, as mentioned above, all the components infiber laser100 are optically coupled by fiber optic cables, although in particular, an EYDF and fiber pump diodes are optically coupled within a fiber laser via fiber optic cables.Fiber pump diodes304 and308 each generate a beam of light, for pumpingEYDF306, on the order of tens of watts.
• Band pass filter300 provides the double amplified beam of light to inputcombiner302.Input combiner302 provides the double amplified beam of light toEYDF306, which will amplify the already double amplified beam of light a third time. This amplification is achieved by usingfiber pump diodes304 and308, which pumpEYDF306 from both ends.Input combiner302 allows the beam of light produced byfiber pump diode304 to be combined with the double amplified beam of light such that it can be amplified a third time. It is noted that inbooster stage288, the double amplified beam of light is passed throughEYDF306 only once.
• EYDF306 is optically coupled withoutput combiner310 viafiber optic cable309₄. In another embodiment of the disclosed technique,EYDF306 can also be coupled withoutput combiner310 directly.Pump diode308 is optically coupled withoutput combiner310 viafiber optic cable309₅.Output combiner310 outputs the triple amplified beam of light to interface312, which provides the triple amplified beam of light tooptical assembly314, which transmits the beam of light towards a volume of interest. The average output power of the output beam of light, after being amplified thrice, can range from 5 to 10 watts.
• In general, in prior art LIDAR systems, an output combiner is physically attached to a laser. If the output beam of light needs to be provided to another system, like an optical system, then the other system either has to be physically attached to the output combiner, or a delivery fiber needs to be used to provide the output beam of light from the output combiner to the other system. Physically attaching the other system to the output combiner can be bulky and cumbersome, as the laser may be relatively large. Furthermore, in this case, coupling the laser with an aiming sight would be impossible. Using a delivery fiber is also not ideal, as delivery fibers can cause losses in the output beam of light, increase the price of the LIDAR system and reduce the overall reliability of the LIDAR system.
• According to the disclosed technique,output combiner310 does not need to be physically attached tofiber laser282, asfiber optic cables309₄and309₅couple EYDF306 andfiber pump diode308 tooutput combiner310. Since fiber optic cables are thin, narrow and flexible,output combiner310 can be distanced fromfiber laser282, and directly coupled withoptical assembly314. In general, sinceoutput combiner310 is much lighter in weight thanfiber laser282, it is feasible to coupleoutput combiner310 withoptical assembly314, which could be, for example, an aiming sight. In this respect, the output beam of light offiber laser282 can be provided directly tooptical assembly314, in a cost efficient manner, without significant losses.
• Reference is now made toFIG. 5A, which is a schematic illustration of a system, generally referenced320, constructed and operative in accordance with a further embodiment of the disclosed technique.System320 includes afiber laser324, acontroller325, amotion detector326 and avehicle322.Fiber laser324 is coupled withcontroller325 which is coupled withmotion detector326.Fiber laser324,controller325 andmotion detector326 are each coupled withvehicle322.Fiber laser324 is constructed and operative in a manner similar to fiber laser100 (FIG. 1B).Motion detector326 can be any unit enabled to detect and determine the motion ofvehicle322, as well as the motion offiber laser324 with respect tovehicle322. For example,motion detector326 can be a gyroscope, an inertial navigation sensor (herein abbreviated INS) and the like, as is known in the art. It is noted that according to one embodiment of the disclosed technique,fiber laser324 is firmly attached tovehicle322.
• According to another embodiment of the disclosed technique,fiber laser324 is attached to a gimbals (not shown), where it is free to move in a plurality of directions, which is firmly attached tovehicle322. In the embodiment wherefiber laser324 is firmly attached tovehicle322,motion detector326 detects and determines the motion ofvehicle322 with respect to the Earth.Motion detector326 can also determine the position ofvehicle322 with respect to the Earth. In the embodiment wherefiber laser324 is attached to the gimbals,motion detector326 detects and determines the motion ofvehicle322 as well as the motion offiber laser324 with respect tovehicle322, which in turn is determined with respect to the Earth.Motion detector326 can also determine the position offiber laser324 with respect to the Earth. In general, the angular orientation of the fiber laser with respect to the Earth is determined with high accuracy, for example, with an error on the order of one millirad, since the fiber laser is receiving reflections from, and hence creating images of, terrain, as well as objects on the terrain. In order to determine their respective positions on the Earth accurately, the angular orientation as well as the position offiber laser324 needs to be determined with high accuracy. In the description ofFIGS. 5A,5B,6A and6B,fiber laser324 is firmly attached tovehicle322, according to one embodiment of the disclosed technique. It is noted that the technique described inFIGS. 5A,5B,6A and6B could analogously be applied to the embodiment wherefiber laser324 is attached to a gimbals.
• System320 is a LORD system.Fiber laser324 scans a volume of interest (not shown) in front ofsystem320 using pulsed beams of light to detect obstacles, and in particular hard-to-see obstacles, which may be in the volume of interest. According to one embodiment of the disclosed technique,fiber laser324 scans the volume of interest by moving the laser scanner (not shown) in a vehicle plane (not shown), as described in more detail inFIG. 5B.Motion detector326 constantly detects the motion ofvehicle322, and provides a signal tocontroller325 indicative of the motion and changes in the motion of vehicle322 (i.e., velocity, acceleration, a change in speed and a change in the direction of motion). For example,motion detector326 can provide an indication tocontroller325 thatvehicle322 is moving in a straight direction, or thatvehicle322 is turning.Motion detector326 can further provide a more detailed indication tocontroller325 regarding the motion ofvehicle322, by determining the angular velocity and the angular acceleration ofvehicle322, the linear velocity and the linear acceleration ofvehicle322, as well as the rate of change in the direction of motion of vehicle322 (i.e., the LOS of fiber laser324).
• One way of characterizing the pulsed beam of light is the frequency at which the pulses are transmitted to a volume of interest (i.e., not the frequency of radiation which is transmitted during each pulse). The frequency at which the pulses are transmitted can be referred to in numerous ways, for example, as the pulse rate and as the pulse repetition rate (herein abbreviated PRR) of the pulsed beam of light. The PRR can be defined as the number of pulses transmitted per unit time. An increase in the PRR of the pulsed beam of light means that more pulsed beams of light will be transmitted each time period, which requires more energy but which means that a larger area can be scanned per unit of time. A decrease in the PRR of the pulsed beam of light means that less pulsed beams of light will be transmitted each time period, which requires less energy but which also means that a smaller area can be scanned per unit of time. It is noted that with regards toFIGS. 5A,5B,6A,6B and13, the term PRR is used as an example, and can be replaced by other ways of referring to the frequency at which pulses are transmitted, for example, the pulse rate (i.e., the rate at which pulses are transmitted). As explained below, the PRR offiber laser324 can be adjusted according to the detected motion ofvehicle322. It is noted that, according to the disclosed technique, adjustments are made to the PRR in order to maintain the scan density of the pulsed beams of light if this is desired by the operator ofvehicle322.
• In general, ifvehicle322 is traveling in a straight direction at low speeds (i.e., linear velocity is low), then a lower PRR can be used to scan the area in front ofvehicle322. As the linear velocity increases, an increase in the PRR is needed if the scan density (i.e., the number of pulsed beams of light transmitted to an area per unit time) is to remain constant. A decrease in the scan density means that the image received from the pulsed beams of light will be of lower resolution and quality, since fewer beams are transmitted to the scanned area per unit time. Also, as the angular velocity increases (e.g., asvehicle322 executes a turn), the path of the vehicle becomes more determined, whereas if the angular velocity decreases (e.g., asvehicle322 straightens out), the path of the vehicle becomes more uncertain. For example, ifvehicle322 is a helicopter traveling in a straight direction, then the likelihood of the helicopter changing course (i.e., moving left, right, up or down) is high compared to the situation of a helicopter which is already veering in a particular direction. In the latter situation, the likelihood is low that the helicopter will change its course before completing its current change of course. At high angular velocities, since the path ofvehicle322 becomes more determined, a smaller area can be scanned and therefore a lower PRR can be used. As the angular velocity ofvehicle322 decreases, a larger area needs to be scanned because of the increasing uncertainty of the path of the vehicle. Therefore, as the angular velocity ofvehicle322 decreases, a higher PRR should be used. It is noted that the operator ofvehicle322 is not limited to human beings. The operator can also be computer software written to autonomously operatevehicle322. Information about obstacles in front of an operator is received from pulsed beams of light transmitted byfiber laser324. In order to increase the energy efficiency ofsystem320, and to provide an operator with information about obstacles in front of her with enough time for her to avoid them,controller325 adjusts the PRR of the pulsed beams of light transmitted byfiber laser324 according to the detected motion ofsystem320.
• Also, whenvehicle322 is traveling in a straight direction at high speeds (i.e., linear velocity is high), the output peak power offiber laser324 is increased bycontroller325 so as to provide an increase in the detection range in front ofvehicle322 ofsystem320. Therefore, as the linear velocity increases, the PRR and the output peak power offiber laser324 increases, and as the linear velocity decreases, the PRR and the output peak power offiber laser324 also decreases. These adjustments to the PRR and the output peak power are further explained with reference toFIGS. 6A and 6B.
• Reference is now made toFIG. 5B, which is a schematic illustration of a helicopter, generally referenced328, mounted with the system320 (FIG. 5A, not shown), constructed and operative in accordance with another embodiment of the disclosed technique.Helicopter328 includes anoperator329, and a laser scanner330 (which is part of system320).Laser scanner330 is enabled to scan in a 2-D plane331, which can be referred to as the vehicle plane. The vehicle plane can be defined by the main longitudinal and latitudinal axes ofhelicopter328. InFIG. 5B,vehicle plane331 is perpendicular to the drawing sheet. As depicted byarrows332_Aand332_B,laser scanner330 scans in a direction parallel tovehicle plane331.FIG. 5B depictshelicopter328 in three different positions,positions335_A,335_Band335_C. Inposition335_A,vehicle plane331 is parallel to ahorizon336. Inposition335_B,vehicle plane331 forms an angle α (not shown), depicted byarrow333, withhorizon336. Inposition335,vehicle plane331 forms an angle β (not shown), depicted byarrow334, withhorizon336. Inpositions335_Band335_C, ashelicopter328 changes orientation,vehicle plane331 changes orientation accordingly, as doeslaser scanner330. According to the disclosed technique,vehicle plane331, as depicted inFIG. 5B, is fixed in its orientation in relation tohelicopter328. According to an embodiment of the disclosed technique, the laser scanner only scans in the 2-D vehicle plane. According to another embodiment, the laser scanner can also scan outside the 2-D vehicle plane.
• Reference is now made toFIG. 6A, which is a schematic illustration of changes to the PRR as a function of the linear motion of a vehicle mounted with system320 (FIG. 5A), constructed and operative in accordance with a further embodiment of the disclosed technique. Each ofvehicles340 and345 are mounted withsystem320. Two pulsed beams oflight342 and347, each transmitted bysystem320, are schematically illustrated inFIG. 6A. Pulsed beam oflight342 corresponds to a pulsed beam of light transmitted fromvehicle340, and pulsed beam oflight347 corresponds to a pulsed beam of light transmitted fromvehicle345. Pulsed beam oflights342 and347 each have an individual pulse duration spanning atime duration343 and a pulse period spanning atime duration344. InFIG. 6A,vehicles340 and345 are depicted as helicopters.Helicopter340 is moving in a straight direction at a low speed, as depicted by athin arrow341.Helicopter345 is moving in a straight direction at a high speed, as depicted by athick arrow346. The linear and angular velocity and acceleration ofhelicopters340 and345 are constantly detected by motion detector326 (FIG. 5A). Sincehelicopter340 is traveling in a straight direction, at a low linear velocity, the PRR of pulsed beam oflight342 is low (e.g., one pulse per pulse period). Sincehelicopter345 is traveling in a straight direction, at a high linear velocity, the PRR of pulsed beam oflight347 is high (e.g., two pulses per pulse period).
• In the situation ofhelicopter340, the PRR is low becausehelicopter340 is traveling at a low linear velocity. Sincehelicopter340 will be covering less distance per unit time, a lower PRR can be used to scan the area in front ofhelicopter340, thereby not expending energy uselessly. Also, sincehelicopter340 will be covering less distance at lower speeds, the output peak power of fiber laser324 (FIG. 5A) can be reduced, since only objects in the near vicinity ofhelicopter340 will be of interest to the pilot. Furthermore, at lower speeds, the FOV of the scan (not shown) is reduced, as described below inFIG. 8B, therefore the PRR can be lowered to maintain the scan density of the pulsed beams of light (not shown). Also, since the reaction time of the operator is increased at lower speeds, the output peak power can be reduced as the operator will have more time to react to objects and obstacles in her path. In the situation ofhelicopter345, the PRR is high becausehelicopter345 is traveling at a high linear velocity. Sincehelicopter345 will be covering more distance per unit time, and since the FOV of the scan will be increased, as described further below inFIG. 8C, a high PRR is needed to scan the area in front ofhelicopter345 if a constant scan density is to be kept and maintained. Also, sincehelicopter345 will be covering more distance at higher speeds, the output peak power offiber laser324 is increased so that objects which are much farther in front ofhelicopter345 can be detected, such as objects located a few hundred meters, or a few kilometers in front of the helicopter. At higher speeds, since the reaction time of the pilot is reduced, an increase in the output peak power offiber laser324 is needed to enable the operator to perceive objects at a further distance in front of the helicopter.
• Motion detector326 also constantly detects the linear velocity and the linear acceleration ofhelicopter340, which substantially determines the most significant volume of interest to the pilot, with controller325 (FIG. 5A) adjusting the PRR as well as the output peak power of pulsed beams oflight342 and347 (both not shown) accordingly. As either the linear velocities ofhelicopters340 and345, the linear accelerations ofhelicopters340 and345, or both, increase, the significant volume of interest lies farther in front of the helicopters, since at high speeds, more distance is covered. Ifhelicopters340 and345 travel in a straight direction at high speeds, which increases the distance of the field of interest to the pilot and also reduces the reaction time of the pilot, thencontroller325 increases the PRR as well as the output peak power offiber laser324. Ifhelicopters340 and345 travel in a straight direction at low speeds, which reduces the distance of the field of interest to the pilot and also increases the reaction time of the pilot, thencontroller325 decreases the PRR as well as the output peak power offiber laser324.
• The PRR and output peak power offiber laser324 are increased ifhelicopter340 travels in a straight direction at high speeds sincehelicopter340 will traverse greater distances in a given time period than when traveling at low speeds in a straight direction. At high speeds, the probability of the pilot being in need of information regarding obstacles located further in her LOS (hence an increase in the output peak power of fiber laser324) is increased since she will be approaching them at an increased rate and she will therefore have less time to react. Furthermore, since greater distances are being traversed, a more rapid rate of pulses needs to be transmitted to maintain the quality of the received image. As depicted inFIG. 6A,controller325 changes the PRR and the output peak power offiber laser324 according to the detected linear motion of a vehicle using an increasing function. The increasing function could be, for example, a direct linear relation, an exponential growth function, and the like. In general, the PRR and output peak power are adjusted according to a change in the linear velocity of the vehicle. Also, the PRR and the output peak power are adjusted according to changes in the FOV of the scan, as described below inFIGS. 8B,8C,8D and8E. Changes in the linear acceleration of the vehicle can be used to correct any errors in the changes in the PRR as a function of changes in the linear velocity of the vehicle. It is noted that the change in PRR as a function of the detected linear motion is optional and is at the discretion of the pilot, since the change in PRR is used to maintain a constant scan density.
• Reference is now made toFIG. 6B, which is a schematic illustration of changes to the PRR as a function of the angular motion of a vehicle, mounted with system320 (FIG. 5A), constructed and operative in accordance with another embodiment of the disclosed technique. Each ofvehicles350 and356 are mounted withsystem320. Two pulsed beams oflight352 and357, each transmitted bysystem320, are schematically illustrated inFIG. 6B. Pulsed beam oflight352 corresponds to a pulsed beam of light transmitted fromvehicle350, and pulsed beam oflight357 corresponds to a pulsed beam of light transmitted fromvehicle356. Pulsed beams oflight352 and357 each have an individual pulse duration spanning atime duration353 and a pulse period spanning atime duration354. InFIG. 6B,vehicles350 and356 are depicted as helicopters.Helicopter350 is moving in a straight direction (i.e., its angular velocity is low), as depicted by anarrow351.Helicopter356 is moving in a curved direction, constantly changing its orientation (i.e., its angular velocity is high), as depicted by anarrow355. The linear and angular velocity and acceleration ofhelicopters350 and356 are constantly detected by motion detector326 (FIG. 5A). Since the direction of travel ofhelicopter350 is likely to change, becausehelicopter350 is traveling in a straight direction, the PRR of pulsed beam oflight352 is increased by controller325 (FIG. 5A). Since the direction of travel ofhelicopter356 is not likely to change, and it more predictable, the PRR of pulsed beam oflight357 is reduced bycontroller325. As can be seen inFIG. 6B, the PRR of pulsed beam oflight352 is double that of pulsed beam oflight357.
• In the situation ofhelicopter350, the PRR is increased because the pilot needs to see obstacles in front of her that are nearby, as her LOS is unpredictable and likely to change. Due to the increased unpredictability of the flight path ofhelicopter350, the FOV of the scan (not shown) is increased, as described below inFIG. 8D. In order to maintain the scan density of the pulsed beams of light (not shown), the PRR is also increased. Since the PRR is high, andhelicopter350 is traveling in a straight direction,system320 will expend extra energy by giving the pilot information about obstacles in front of her at a faster rate, since such information is needed by the pilot to avoid obstacles in the case thathelicopter350 turns and curves. In the situation ofhelicopter356, the PRR is decreased because the pilot only needs to see obstacles in her flight path, since her LOS is more predictable and not likely to change. Due to the increased predictability of the flight path ofhelicopter356, the FOV of the scan (not shown) is decreased, as described inFIG. 8E. In order to maintain the scan density of the pulsed beams of light (not shown), the PRR is also decreased. Since the PRR is low, andhelicopter356 is traveling in a curved direction,system320 will expend less energy by giving the pilot information about obstacles directly in her flight path, since only such information is needed by the pilot to avoid obstacles in the case thathelicopter356 continues in its flight path.
• Motion detector326 constantly detects at least one of the angular velocity and the angular acceleration ofhelicopters350 and356, which substantially determines the field of interest to the pilot, withcontroller325 adjusting the PRR accordingly, as explained above. In the case ofhelicopter356 traveling in a curved direction, which narrows the field of interest to the pilot,controller325 decreases the PRR offiber laser324. In the case ofhelicopter350 traveling in a straight direction, which widens the field of interest to the pilot,controller325 increases the PRR offiber laser324.
• The PRR offiber laser324 is increased as the angular velocity ofhelicopter350 decreases, since the flight path ofhelicopter350 will be more uncertain in a given time period than when traveling at higher angular velocities. At high angular velocities, the probability of the pilot being in need of information regarding obstacles located outside the flight path is decreased, for example inhelicopter356, since a curved flight path is more predictable of the current general motion of the helicopter than a straight flight path. As such, the FOV of the scan is decreased, as described below inFIG. 8E.
• In general, the change in PRR of the pulsed beam of light is a function of the degree to which the direction of vehicle322 (FIG. 5A) changes (i.e., either the angular velocity, the angular acceleration, or both). The change in PRR of the pulsed beam of light is also a function of the change in the FOV of the scan, since the PRR is modified to maintain the scan density if the FOV of the scan is changed. It is noted that in the embodiment wherefiber laser324 is attached to a gimbals, the change in PRR of the pulsed beam of light is a function of the degree to which the direction offiber laser324 changes with respect tovehicle322. A quicker change in direction ofvehicle322, for example, whenvehicle322 executes a sharper turn, will result in a larger decrease in the PRR of the pulsed beam of light, as compared with a slower change in direction ofvehicle322, for example, whenvehicle322 executes a wide turn. Furthermore, as described inFIG. 6A, the change in PRR as well as output peak power offiber laser324 is a function of either the linear velocity ofvehicle322, the linear acceleration ofvehicle322, or both, which is itself a factor that substantially determines the field of interest to the pilot. Since the change in PRR is a function of the change in direction ofvehicle322 as well as the change in at least one of the linear velocity and in the linear acceleration ofvehicle322, each in different ways, in one embodiment of the disclosed technique, both changes are taken into account bycontroller325 whencontroller325 adjusts the PRR offiber laser324. For example, ashelicopter350 travels in more of a straight direction,controller325 increases the PRR offiber laser324 yet also factors in the linear velocity ofhelicopter350. If, while traveling in a straight direction,helicopter350 then travels at a higher speed than its current speed,controller325 increases the PRR offiber laser324, and may increase the output peak power offiber laser324 as well. In another embodiment of the disclosed technique, either only the angular velocity ofvehicle322, only the angular acceleration ofvehicle322, or both, are taken into account when adjusting the PRR offiber laser324. In a further embodiment of the disclosed technique, either only the linear velocity ofvehicle322, only the linear acceleration ofvehicle322, or both, are taken into account when adjusting the PRR and the output peak power offiber laser324.
• Motion detector326 (FIG. 5A) constantly detects the angular motion ofvehicle322, andcontroller325 constantly adjusts the PRR of the pulsed beam of light accordingly. As the change in direction (i.e., either the angular velocity, the angular acceleration, or both) ofvehicle322 increases, the PRR of the pulsed beam of light decreases, and as the change in direction ofvehicle322 decreases, the PRR of the pulsed beam of light increases. Furthermore, as described inFIG. 6A, the PRR as well as output peak power offiber laser324 are adjusted according to the linear velocity ofvehicle322, the linear acceleration ofvehicle322, or both, by an increasing function, which in turn substantially determines the field of interest to the pilot. Therefore, as the field of interest to the pilot changes, the PRR, as well as the output peak power, offiber laser324 are changed as well bycontroller325. As depicted inFIG. 6B,controller325 changes the PRR offiber laser324 according to the detected angular motion of a vehicle using a decreasing function. The decreasing function could be, for example, an inverse relation, an exponential decay function, and the like. In general, the change in PRR is a function of a change in the angular velocity of the vehicle. Changes in the angular acceleration of the vehicle can be used to correct any errors in the changes in the PRR as a function of changes in the angular velocity of the vehicle.
• Reference is now made toFIG. 7, which is a schematic illustration of a system, generally referenced380, constructed and operative in accordance with a further embodiment of the disclosed technique.System380 includes afiber laser384, acontroller385, amotion detector386 and avehicle382.Fiber laser384 is coupled withcontroller385 which is coupled withmotion detector386.Fiber laser384,controller385 andmotion detector386 are each coupled withvehicle382.Fiber laser384 is constructed and operative in a manner similar to fiber laser100 (FIG. 1B).Motion detector386 can be any unit enabled to detect and determine the speed as well as the motion of vehicle382 (i.e., linear velocity and linear acceleration, angular velocity and angular acceleration, a combination thereof and the like). For example,motion detector386 can be a gyroscope, an INS and the like, as is known in the art.
• System380 is a LORD system.Fiber laser384 scans a volume of interest (not shown) in front ofsystem380 using pulsed beams of light to detect obstacles, and in particular hard-to-see obstacles, which may be in the volume of interest.Motion detector386 constantly detects the speed ofvehicle382, as well as the motion of vehicle382 (i.e., changes in the direction of motion of the vehicle) and provides a signal tocontroller385 indicative of the changes in speed, and motion, ofvehicle382. For example,motion detector386 can provide an indication tocontroller385 thatvehicle382 is moving at a particular speed, in a straight direction (i.e., linear velocity and linear acceleration) or in a curved direction (i.e., angular velocity and angular acceleration).
• One way of characterizing the volume of interest scanned bysystem380 is the width of the field-of-view (herein abbreviated FOV) in the vehicle plane (as described inFIG. 5B) ofsystem380. The FOV refers to the particular volume ofinterest system380 scans for obstacles in the vehicle plane. Since the vehicle plane is stationary, as the vehicle moves, the vehicle plane moves as well, causing the FOV to move also. The width of the FOV refers to the spread angle of the FOV when viewed from a top orthogonal view, as explained in further detail with reference toFIG. 8A. Another way of characterizing the FOV is the LOS of the scan, which refers to a vector that bisects the area covered by the FOV into equal parts.
• The width of the FOV is a measure of how large a volume of interest is scanned bysystem380. An increase in the width of the FOV means that a larger volume of interest will be scanned, which requires more energy and time. A decrease in the width of the FOV means that a smaller volume of interest will be scanned, which requires less energy and time.
• In general, ifvehicle382 is traveling at high speeds, then the likelihood that an operator ofvehicle382 will need to know information about obstacles which are significantly off-centered from her LOS is increased, sincevehicle382 will be covering more distance per unit time and the reaction time of the operator will be reduced. It is noted that the operator ofvehicle382 is not limited to human beings. The operator can also be computer software written to autonomously operatevehicle382. Furthermore, sincevehicle382 will traverse a greater distance in less time at high speeds, there is more of a need forsystem380 to scan the entire volume of interest. On the other hand, ifvehicle382 is not traveling at high speeds, but is traveling at low speeds, then the likelihood that the operator ofvehicle382 will need to know information about obstacles which are significantly off-centered from her LOS is decreased, sincevehicle382 will be covering less distance per unit time and the reaction time of the operator is increased. At low speeds, the most significant obstacles tovehicle382 will lie directly in the LOS of the operator.
• Also, ifvehicle382 is traveling in a straight direction (i.e., low angular velocity), then the likelihood that an operator ofvehicle382 will need to know information about obstacles in front of her and significantly off-centered from her LOS is increased, since the path ofvehicle382 will be less predictable. On the other hand, ifvehicle382 is not traveling in a straight direction, but is turning (i.e., high angular velocity), then the likelihood that the operator ofvehicle382 will need to know information about obstacles which are significantly off-centered from her LOS is reduced, since the path ofvehicle382 will be more predictable.
• Furthermore, asvehicle382 changes orientation (i.e., turns), the LOS of the scan needs to be adjusted to follow the path of the vehicle. As the angular velocity ofvehicle382 increases, the LOS of the scan needs to be adjusted quicker, since the change in direction ofvehicle382 increases as well. Likewise, as the angular velocity ofvehicle382 decreases, the LOS of the scan can be adjusted slower, since the change in direction ofvehicle382 decreases as well. By adjusting the LOS of the scan according to the angular motion ofvehicle382, the operator can get an image of the location wherevehicle382 will be in a certain amount of time. For example, ifvehicle382 is turning to the right by 90 degrees, by adjusting the LOS of the scan whilevehicle382 is turning, the operator of the vehicle can get an image of thelocation vehicle382 will be at when the turn is complete, which may be, for example, in 5 seconds.
• Also, sincevehicle382 will traverse a smaller distance in more time at low speeds, there is more time forsystem380 to scan the entire volume of interest. In order to provide an operator with information about obstacles in front of her with enough time for her to avoid them,controller385 adjusts the width of the FOV ofsystem380 according to the determined speed and motion ofsystem380. This adjustment to the width of the FOV, as well as to the LOS of the scan, ofsystem380 is further explained with reference toFIGS. 8A,8B,8C,8D,8E,8F and8G.
• Reference is now made toFIG. 8A, which is a schematic illustration of a vehicle mounted with system380 (FIG. 7), generally referenced400, constructed and operative in accordance with another embodiment of the disclosed technique.FIG. 8A depicts the difference between the FOV and the field-of-regard (herein abbreviated FOR) ofvehicle400.FIG. 8A also depicts the LOS of the scan. InFIG. 8A,vehicle400 is a helicopter.FIG. 8A is a top orthogonal view ofhelicopter400.
• The FOR ofsystem380 refers to the volume of interest whichsystem380 can possibly scan for obstacles, whereas the FOV ofsystem380 refers to the volume of interest whichsystem380 actually scans. The FOR ofsystem380 is limited by the mechanics ofsystem380 and the range ofangles system380 can be directed at. In general, the FOV is significantly smaller than the FOR, becausesystem380 cannot scan the entire FOR fast enough to provide real-time up-to-date information regarding obstacles in the flight path ofhelicopter400. The FOR and the FOV ofsystem380 can be defined in terms of the width of the spread angle each makes with the volume of interest. InFIG. 8A, the FOR ofsystem380 has aspread angle408, whose width is delineated by arange404. The FOV ofsystem380 has aspread angle406, whose width is delineated by arange402. The FOR ofsystem380 may be for example 100°, and the FOV ofsystem380 may be for example 25°. As the spread angle increases, so does the width of the spread angle.Arrow407 represents the LOS of the scan, as it bisects the FOV ofsystem380 into equal parts. The LOS of the scan represents the general direction of the FOV.
• Reference is now made toFIG. 8B, which is a schematic illustration of a vehicle mounted with system380 (FIG. 7), generally referenced410, constructed and operative in accordance with a further embodiment of the disclosed technique.FIG. 8B depicts the change in FOV ofsystem380 as either the linear velocity ofvehicle410, the linear acceleration ofvehicle410, or both, decrease (depicted by a thin arrow416). InFIG. 8B,vehicle410 is a helicopter.FIG. 8B is a top orthogonal view ofhelicopter410.
• InFIG. 8B, the FOV ofsystem380 is constantly adjusted by controller385 (FIG. 7) according to at least one of the linear velocity ofhelicopter410 and the linear acceleration ofhelicopter410. The speed ofhelicopter410 is therefore constantly detected by motion detector386 (FIG. 7). Ashelicopter410 decreases in speed, aspread angle417 of the FOV ofsystem380 is decreased bycontroller385, thereby decreasing a range412 of the width of the spread angle of the FOV ofsystem380. Sincehelicopter410 is traveling at slower speeds, thereby resulting in less of a need forsystem380 to scan a large FOV (since less distance is covered and the time in which the pilot can react is increased), the FOV ofsystem380 is decreased so that only the most significant volume of interest, where obstacles to helicopter410 can be found, is scanned. This significant volume of interest lies directly in the LOS ofhelicopter410 at low speeds. Also, since the time in which the pilot can react is increased, i.e., the look ahead distance is increased, the FOV ofsystem380 can be reduced. The look ahead distance can be defined as the distance along the ground track of an aircraft in flight that marks the outer limits of a collision alert envelope, which is a function of the speed of the aircraft and the time to complete an evasive maneuver (e.g., to avoid a collision). It is noted that aspread angle418, and arange414 of the width of the spread angle of the FOR, ofsystem380, do not change with a change in speed ofhelicopter410.
• Reference is now made toFIG. 8C, which is a schematic illustration of a vehicle mounted with system380 (FIG. 7), generally referenced420, constructed and operative in accordance with another embodiment of the disclosed technique.FIG. 8C depicts the change in FOV ofsystem380 as the linear velocity ofvehicle420, the linear acceleration ofvehicle420, or both, increase (depicted by a thick arrow426). InFIG. 8C,vehicle420 is a helicopter.FIG. 8C is a top orthogonal view ofhelicopter420.
• InFIG. 8C, the FOV ofsystem380 is constantly adjusted according to at least one of the linear velocity ofhelicopter420 and the linear acceleration ofhelicopter420 by controller385 (FIG. 7). The speed ofhelicopter420 is therefore constantly detected by motion detector386 (FIG. 7). Ashelicopter420 increases in speed, aspread angle427 of the FOV ofsystem380 is increased bycontroller385, thereby increasing arange422 of the width of the spread angle of the FOV ofsystem380. Sincehelicopter420 is traveling at higher speeds (since more distance is covered and the time in which the pilot can react, i.e., the look ahead distance, is decreased), thereby resulting in more of a need forsystem380 to scan a larger FOV, the FOV ofsystem380 is increased so that a larger volume of interest, where obstacles to helicopter420 can be found, is scanned. This larger volume of interest lies directly in the LOS ofhelicopter420, as well as off-center from the LOS ofhelicopter420, at higher speeds. It is noted that aspread angle428, and arange424 of the width of the spread angle of the FOR, ofsystem380, do not change with a change in speed ofhelicopter420.
• The change in FOV is a function of at least one of the detected linear velocity ofvehicle382 and the linear acceleration of vehicle382 (FIG. 7). The change in FOV is also a function of the motion ofvehicle382. In one embodiment of the disclosed technique, only either the linear velocity ofvehicle382, the linear acceleration ofvehicle382, or both, are taken into account when adjusting the FOV ofsystem380. In general, the FOV is adjusted in accordance with the linear velocity ofvehicle382 by an increasing function. The linear acceleration ofvehicle382 can be used to correct for errors in the change of the FOV as a function of the linear velocity, as is known in the art. For example, ashelicopter420 travels at increasing speeds,controller385 increases the FOV ofsystem380. In another embodiment of the disclosed technique, the pilot can adjust the FOV manually, thereby overriding the changes to the FOV as determined bycontroller385 in relation to the changes in speed and motion ofvehicle382. It is noted, as was described inFIGS. 5A and 6A, that as the linear velocity increases, the FOV ofsystem380 is increased, as well as the PRR and the output peak power of fiber laser384 (FIG. 7), and that as the linear velocity decreases, the FOV ofsystem380 is decreased, as well as the PRR and the output peak power offiber laser384. The PRR is generally adjusted according to changes in the FOV in order to maintain a constant scan density of pulsed beams of light. If the FOV ofsystem380 increases, then the PRR needs to be increased to maintain the scan density, and if the FOV ofsystem380 decreases, then the PRR needs to be decreased to maintain the scan density.
• Reference is now made toFIG. 8D, which is a schematic illustration of a vehicle mounted with system380 (FIG. 7), generally referenced430, constructed and operative in accordance with a further embodiment of the disclosed technique.FIG. 8D depicts the change in FOV ofsystem380 as the angular velocity ofvehicle430, the angular acceleration ofvehicle430, or both, decrease (depicted by anarrow433 with a slight curvature). InFIG. 8D,vehicle430 is a helicopter.FIG. 8D is a top orthogonal view ofhelicopter430.
• InFIG. 8D, the FOV ofsystem380 is constantly adjusted according to at least one of the angular velocity ofhelicopter430 and the angular acceleration ofhelicopter430 by controller385 (FIG. 7). The angular motion ofhelicopter430 is therefore constantly detected by motion detector386 (FIG. 7). Ashelicopter430 decreases in angular velocity (i.e., a light turn), aspread angle429 of the FOV ofsystem380 is increased bycontroller385, thereby increasing arange431 of the width of the spread angle of the FOV ofsystem380. Since the angular velocity ofhelicopter430 is low, the flight path of the helicopter is less predictable. This reduction in angular velocity results in a need forsystem380 to scan a larger FOV, therefore, the FOV ofsystem380 is increased. It is noted that the spread angle (not shown) of the FOR, and the range of the width (not shown) of the FOR, ofsystem380, do not change with a change in angular velocity ofhelicopter430.
• Reference is now made toFIG. 8E, which is a schematic illustration of a vehicle mounted with system380 (FIG. 7), generally referenced435, constructed and operative in accordance with another embodiment of the disclosed technique.FIG. 8E depicts the change in FOV ofsystem380 as the angular velocity ofvehicle435, the angular acceleration ofvehicle435, or both, increase (depicted by anarrow440 with a large curvature). InFIG. 8E,vehicle435 is a helicopter.FIG. 8E is a top orthogonal view ofhelicopter435.
• InFIG. 8E, the FOV ofsystem380 is constantly adjusted according to at least one of the angular velocity ofhelicopter435 and the angular acceleration ofhelicopter435 by controller385 (FIG. 7). The angular motion ofhelicopter435 is therefore constantly detected by motion detector386 (FIG. 7). Ashelicopter435 increases in angular velocity (i.e., a sharp turn), aspread angle436 of the FOV ofsystem380 is decreased bycontroller385, thereby decreasing arange438 of the width of the spread angle of the FOV ofsystem380. Since the angular velocity ofhelicopter435 is high, the flight path of the helicopter is more predictable. As such,system380 does not need to scan a large FOV, resulting in the FOV ofsystem380 being decreased. It is noted that the spread angle (not shown) of the FOR, and the range of the width (not shown) of the FOR, ofsystem380, do not change with a change in angular velocity ofhelicopter435.
• The FOV ofsystem380 can be changed in relation to the detected angular motion (e.g., changes in angular velocity, in angular acceleration, or both) of helicopter435 (not shown). For example, ifhelicopter435 is traveling in a straight direction (i.e., low angular velocity), then the FOV ofsystem380 is increased accordingly. The FOV is increased because the flight path ofsystem380 in more likely to change. Therefore, obstacles directly in front ofhelicopter435 as well as those that are significantly off-centered from the LOS of the pilot are detected by increasing the FOV. If, on the other hand, the helicopter is not traveling in a straight direction, but in a curved direction (i.e., either high angular velocity, high angular acceleration, or both), then the FOV ofsystem380 is decreased. Whenhelicopter435 travels in a curved direction, the FOV ofsystem380 is decreased because the LOS of the pilot is more predictable as is the flight path ofhelicopter435. In general, the FOV is adjusted in accordance with the angular velocity ofvehicle382 by a decreasing function. The angular acceleration ofvehicle382 can be used to correct for errors in the change of the FOV as a function of the angular velocity, as is known in the art. It is noted, as was described inFIGS. 5A and 6B, that as the angular velocity increases, the FOV is decreased, as well as the PRR of fiber laser384 (FIG. 7), and that as the angular velocity decreases, the FOV is increased, as well as the PRR offiber laser384. As mentioned above with reference toFIG. 8C, the PRR is generally adjusted according to changes in the FOV in order to maintain a constant scan density of pulsed beams of light. If the FOV ofsystem380 increases, then the PRR needs to be increased to maintain the scan density, and if the FOV ofsystem380 decreases, then the PRR needs to be decreased to maintain the scan density.
• Reference is now made toFIG. 8F, which is a schematic illustration of a vehicle mounted with system380 (FIG. 7), generally referenced441, constructed and operative in accordance with a further embodiment of the disclosed technique.FIG. 8F depicts the change in the LOS of the scan ofsystem380 as the angular velocity ofvehicle441, the angular acceleration ofvehicle441, or both, decrease (depicted by anarrow447 with a slight curvature). InFIG. 8F,vehicle441 is a helicopter.FIG. 8F is a top orthogonal view ofhelicopter441.
• InFIG. 8F, the LOS of the scan ofsystem380 is constantly adjusted according to at least one of the angular velocity ofhelicopter441 and the angular acceleration ofhelicopter441 by controller385 (FIG. 7). The angular motion ofhelicopter441 is therefore constantly detected by motion detector386 (FIG. 7). Ashelicopter441 decreases in angular velocity (i.e., a light turn), aninitial FOV444, with the LOS of the scan being represented by an arrow443_A, is adjusted in the direction of motion ofhelicopter441, to afinal FOV445. The LOS of the scan forfinal FOV445 is depicted by an arrow443_B.Initial FOV444 has been moved by an angle γ (not shown), depicted by anarrow446, tofinal FOV445. By adjusting the LOS of the scan of the FOV ofhelicopter441 according to the angular motion of the helicopter, a pilot can get an image of the location where the helicopter will be in a certain amount of time. As the angular velocity ofhelicopter441 decreases, the angle depicted byarrow446 also decreases, since the change in orientation ofhelicopter441 is reduced when the angular velocity is low. It is noted that the spread angle (not shown) of the FOR, and the range of the width (not shown) of the FOR, ofsystem380, do not change with a change in the LOS of the scan ofhelicopter441.
• Reference is now made toFIG. 8G, which is a schematic illustration of a vehicle mounted with system380 (FIG. 7), generally referenced453, constructed and operative in accordance with another embodiment of the disclosed technique.FIG. 8G depicts the change in the LOS of the scan ofsystem380 as the angular velocity ofvehicle453, the angular acceleration ofvehicle453, or both, increase (depicted by anarrow454 with a strong curvature). InFIG. 8G,vehicle453 is a helicopter.FIG. 8G is a top orthogonal view ofhelicopter453.
• InFIG. 8G, the LOS of the scan ofsystem380 is constantly adjusted according to at least one of the angular velocity ofhelicopter453 and the angular acceleration ofhelicopter453 by controller385 (FIG. 7). The angular motion ofhelicopter453 is therefore constantly detected by motion detector386 (FIG. 7). Ashelicopter453 increases in angular velocity (i.e., a sharp turn), aninitial FOV450, with the LOS of the scan being represented by anarrow449_A, is adjusted in the direction of motion ofhelicopter453, to afinal FOV451. The LOS of the scan forfinal FOV451 is depicted by anarrow449_B.Initial FOV450 has been moved by an angle δ (not shown), depicted by anarrow452, tofinal FOV451. By adjusting the LOS of the scan of the FOV ofhelicopter453 according to the angular motion of the helicopter, a pilot can get an image of the location where the helicopter will be in a certain amount of time. It is noted that arrow446 (FIG. 8F) is smaller in size thanarrow452. Therefore, as the angular velocity increases, the difference in angle between the initial FOV and the final FOV of the helicopter also increases. As the angular velocity of the helicopter increases, the visibility of the pilot is reduced since the helicopter is constantly changing orientation. Therefore, as the angular velocity increases, there is a need to increase the visibility of the pilot to ensure her ability to detect obstacles in the flight path of the helicopter. The visibility of the pilot is increased by increasing the angle through which the LOS of the scan is adjusted according to the angular motion of the helicopter.
• For example, as the angular velocity ofhelicopter453 begins to increase, the angle through which the LOS of the scan is moved in, following the change in orientation ofhelicopter453, also increases. As the angular velocity ofhelicopter453 decreases, the angle through which the LOS of the scan is moved in also decreases. It is noted that the spread angle (not shown) of the FOR, and the range of the width (not shown) of the FOR, ofsystem380, do not change with a change in the LOS of the scan ofhelicopter453. In general, the LOS of the scan is adjusted in accordance with the angular velocity ofvehicle382 by an increasing function. The angular acceleration ofvehicle382 can be used to correct for errors in the change of the LOS of the scan as a function of the angular velocity, as is known in the art.
• Reference is now made toFIG. 9, which is a schematic illustration of a double LIDAR system, generally referenced455, constructed and operative in accordance with a further embodiment of the disclosed technique.Double LIDAR system455 includes afiber laser457, anoptical assembly459, a reflecting-transmittingplate456, and tworeceivers458₁and458₂.Fiber laser457 is optically coupled withoptical assembly459.Optical assembly459 is optically coupled with reflecting-transmittingplate456, wherebyoptical assembly459 can provide pulsed beams of light to reflecting-transmittingplate456.Receivers458₁and458₂are optically coupled with reflecting-transmittingplate456, such that reflecting-transmittingplate456 can reflect a pulsed beam of light towardsreceiver458₂and transmit a pulsed beam of light towardsreceiver458₁.
• Reflecting-transmittingplate456 is constructed to reflect beams of light of one wavelength and transmit beams of light of another wavelength.Receivers458₁and458₂are constructed to only receive and detect specific wavelengths of light.
• Fiber laser457 generates two pulsed beams of light which differ only in wavelength. The two pulsed beams of light are separated in time, such that each pulsed beam of light is transmitted at different time.Fiber laser457 provides the two generated pulsed beams of light, one at a time, tooptical assembly459.Optical assembly459 is constructed to transmit the two pulsed beams oflight460₁and460₂towards a volume of interest (not shown). Since pulsed beams oflight460₁and460₂are transmitted at different times, each pulsed beam of light will reflect from a different section of the volume of interest. Pulsed beams oflight460₁and460₂will impinge upon obstacles (not shown) in front ofsystem455 and reflect back tooptical assembly459. Reflected pulsed beams oflight460₃and460₄are then received byoptical assembly459. Reflected pulsed beams oflight460₃and460₄are then directed towards reflecting-transmittingplate456.
• Reflecting-transmittingplate456 is constructed to transmit reflected pulsed beam oflight460₃towardsreceiver458₁, based on its wavelength. Reflecting-transmittingplate456 is also constructed to reflect reflected pulsed beam oflight460₄towardsreceiver458₂, based on its wavelength.Receiver458₁receives reflected pulsed beam oflight460₃, andreceiver458₂receives reflected pulsed beam oflight460₄. It is noted thatreceiver458₁is constructed to only receive and detect the wavelength of reflected pulsed beam oflight460₃, and thatreceiver458₂is constructed to only receive and detect the wavelength of reflected pulsed beam oflight460₄.
• In general LIDARs are set to operate at one operational wavelength. In order to scan a volume of interest with a LIDAR system using two operational wavelengths, two complete LIDAR systems are required. Since the laser used in a LIDAR system is quite bulky and heavy, setting up two complete LIDAR systems on a vehicle can be cumbersome and expensive. In contrast, according to the disclosed technique,double LIDAR system455 allows a single complete LIDAR system to operate at two operational wavelengths and direct reflections of the two operational wavelengths to receivers specific for each wavelength. Accordingly,double LIDAR system455 performs the functionality of two LIDAR systems while taking up the volume of only one LIDAR system. Since the size of a receiver used in a LIDAR is negligible in comparison to the size of the laser used in a LIDAR, adding a second receiver to a LIDAR system, according to the disclosed technique, does not significantly increase the volume of a LIDAR system, whereas adding a second laser to a LIDAR system would significantly increase the volume of a LIDAR system.
• It is noted that usingdouble LIDAR system455, the FOV ofdouble LIDAR system455 can be scanned at twice the rate of a conventional LIDAR system. This doubling of the scan rate is achieved by transmitting a second pulsed beam of light of a different wavelength to the FOV while a first pulsed beam of light is reflecting from objects in the FOV, without having the two pulsed beams of light interfere. Also, during the scanning period of a conventional LIDAR system, the volume of the FOV ofdouble LIDAR system455 can be doubled over the volume of the FOV of a conventional LIDAR system. This doubling of the volume of the FOV ofdouble LIDAR system455 is achieved by transmitting pulsed beams of light at two different operational wavelengths almost simultaneously, to different sections of the FOV ofdouble LIDAR system455. Since twice as many pulsed beams of light can be transmitted bydouble LIDAR system455,double LIDAR system455 can scan twice the volume of the FOV of a conventional LIDAR system.
• Reference is now made toFIG. 10A, which is a schematic illustration of light beams reflecting off of different types of surfaces, constructed and operative in accordance with another embodiment of the disclosed technique.FIG. 10A depicts the difference in how light beams reflect off the surface of asolid object500, and aclutter object512.Solid object500 may be the wall of a building, an antenna, power lines, a pole, or any other target or obstacle of significance to an operator of a vehicle.Solid object500 can be referred to as a hard object.Clutter object512 may be a cloud, dust particles, rain, smoke, snowfall or any other type of weather condition which reduces visibility.Clutter object512 can be referred to as a soft object.
• Whenlight beam502 impinges onsolid object500 atpoint504, sincesolid object500 is solid,light beam502 reflects off ofsolid object500 atpoint504, thereby producing a reflectedlight beam506. A schematic illustration of reflectedlight beam506 is shown as apulse508.Pulse508 is defined by a pulse width in time, which extends over a time range510. In general, sincelight beam502 will not penetratesolid object500 at all (due to the hardness of solid object500), then the pulse width oflight beam502 will be substantially the same as the pulse width of reflectedlight beam506. The pulse width of reflectedlight beam506 may be slightly longer than the pulse width oflight beam502 due to the texture of the surface ofsolid object500 whichlight beam502 impinges on.
• When alight beam514 impinges onclutter object512, sinceclutter object512 is not completely solid,light beam514 will reflect off ofclutter object512 atpoints516_A,516_B,516_Cand516_D. Each point of reflection will thereby produce a reflected light beam, for example reflectedlight beams518_A,518₈,518_Cand518_D. Sincelight beam514 will penetrateclutter object512 at various depths (due to the softness of clutter object512), reflectedlight beams518_A,518_B,518_Cand518_Dwill each be received by a receiver (not shown) at slightly different times, thereby resulting in a single perceived reflected light beam (which is actually many reflected light beams arriving at the receiver in an overlapping manner) with a perceived pulse width which is much large than the pulse width oflight beam514. Since many reflected light beams arrive at the receiver in an overlapping manner, the single perceived reflected light beam can be though of as a “smeared” reflected light beam.
• In this regard, the amount of smearing refers to how overlapped the many reflected light beams are with one another. If the reflected light beams are largely overlapped, then the amount of smearing is low, since the arrival time of each of the reflected light beams is very close to one another. This indicates that the clutter object is significantly solid, as the transmitted light beam only reflected over a small range of depth of the clutter object. If the reflected light beams are barely overlapped, then the amount of smearing is high, since the arrival time of each of the reflected light beams is far from one another. This indicates that the clutter object is not solid at all, as the transmitted light beam reflected over a large range of depths of the clutter object.
• A schematic illustration of the perceived pulse of reflectedlight beams518_A,518_B,518_Cand518_Dis shown as apulse520.Pulse520 is defined by a pulse width in time, which extends overtime range522. The pulse width ofpulse520 is much larger than the pulse width oflight beam514. In general, clutter objects reduce the visibility of an operator of a vehicle. Furthermore, since clutter objects also reflect light beams, clutter objects make it difficult for an operator of a vehicle to discern whether reflected light beams reflected from solid objects or from clutter objects.
• Reference is now made toFIG. 10B, which is a schematic illustration of a system, generally referenced550, for distinguishing reflections from objects and clutter, constructed and operative in accordance with a further embodiment of the disclosed technique.System550 includes afiber laser552, areceiver554, apulse width detector556 and aprocessor558.System550 may be mounted on a vehicle (not shown).Fiber laser552 is coupled withprocessor558.Receiver554 is coupled withprocessor558 and withpulse width detector556.Pulse width detector556 is coupled withprocessor558.Pulse width detector556 can be a notch filter, a plurality of notch filters, a signal processor or any other device enabled to detect the pulse width of a reflected beam of light. In an embodiment of the disclosed technique, if a notch filter is used, then the notch filter should include a plurality of narrow band pass filters. At least one of the narrow band pass filters should include at least one RCL circuit for detecting low, middle and high frequency pulse widths.
• Fiber laser552 generates and transmits a pulsed beam oflight560 towards a volume of interest (not shown). Pulsed beam oflight560 will impinge upon anobject566, which may either be a solid object or a clutter object. A reflected pulsed beam oflight562 will reflect back towardsreceiver554.Receiver554 will receive a reflected pulsed beam oflight564.Pulse width detector556 then detects the pulse width of reflected pulsed beam oflight564. Ifpulse width detector556 is a signal processor, thenpulse width detector556 also detects, and rejects, background signals impinging uponsystem550. Background signals are signals impinging uponreceiver554 which were not initially generated and transmitted by fiber laser552 (i.e., signals other than reflected pulsed beams oflight562 and564). Background signals can be characterized by a signal intensity which is below a predetermined detection threshold.
• Ifpulse width detector556 is a signal processor, then it also adjusts the predetermined detection threshold which differentiates reflected pulsed beam of light564 from background signals, where reflected pulsed beam oflight564 will have an intensity above the predetermined detection threshold, and background signals will have an intensity below the predetermined detection threshold. The predetermined threshold can be adjusted according to the average intensity of detected background signals. Ifpulse width detector556 is a signal processor, it also detects the time of arrival of reflected pulsed beam oflight564, and selects an optimal mode for signal processing reflected pulsed beam oflight564.
• Modes of signal processing the reflected pulsed beam of light can include detecting the rise time of reflected pulsed beam oflight564, detecting the maximum amplitude of reflected pulsed beam oflight564, integrating a plurality of reflected pulsed beams of light and then averaging the detected characteristics of the beams (e.g., the average rise time of the reflected pulsed beams of light), using weighted calculations when determining characteristics of the reflected pulsed beam of light, and the like. The optimal mode can be selected automatically bypulse width detector556 or it can be selected manually by a user. Factors used in determining the optimal mode can include the geographical location and climate wheresystem550 is used (e.g., Israel and a desert climate, Alaska and a tundra climate), as well as whethersystem550 is used over land or over sea.
• In an embodiment of the disclosed technique, using the detected pulse width of reflected pulsed beam oflight564, and the original pulse width of pulsed beam oflight560,processor558 then classifies reflected pulsed beam oflight564 as a reflection from either a solid object or a reflection from a clutter object. In another embodiment of the disclosed technique,processor558 classifies reflected pulsed beam oflight564 according to its amount of smearing. In this embodiment, reflected pulsed beam oflight564 is classified on a scale which ranges from a pure solid object to a pure clutter object. In a further embodiment of the disclosed technique, if a predetermined number of reflected pulsed beams of light are classified as clutter objects in a predetermined time period, thenprocessor558 provides a low visibility indication, indicating that too many clutter objects are present in the volume of interest. Too many clutter objects present in the volume of interest make it difficult forsystem550 to detect the presence of solid objects in the volume of interest.
• Reference is now made toFIG. 11, which is a schematic illustration of a system, generally referenced600, constructed and operative in accordance with another embodiment of the disclosed technique.System600 depicts a LADAR system, which can be mounted on a vehicle (not shown).System600 includes apower supply602, afiber laser604, ahardware controller606, aprocessor608,transceiver optics610, anoptical receiver612, ascanner614, ascanner driver616, anINS618, auser interface620, a helmet mounted display (HMD)symbol generator622 and avoice management unit624.System600 can also include a global positioning system (herein abbreviated GPS), an altimeter and a weight sensor (none shown).
• Hardware controller606 is coupled withpower supply602,fiber laser604,processor608,optical receiver612,scanner614 and withscanner driver616.Processor608 is further coupled withpower supply602,INS618,user interface620,HMD symbol generator622 and withvoice management unit624.Power supply602 is further coupled withfiber laser604.Transceiver optics610 is optically coupled withfiber laser604,optical receiver612 and withscanner614.Scanner614 is further coupled withscanner driver616. The GPS and the altimeter are coupled with the processor. The weight sensor is coupled with the wheels of the vehicle and with the processor.
• Transceiver optics610 includes a plurality of optical elements (not shown), such as a beam combiner (for aligning the transmitted laser beam and the received reflected laser beam onto the same optical axis), a telescope, a deflecting mirror, and the like.Transceiver optics610 is operative to transmit and receive beams of light on a single optical axis.Fiber laser604 is constructed and operative in a manner similar to fiber laser150 (FIG. 2).Hardware controller606 is operative to coordinate and synchronize the operation offiber laser604,scanner driver616 andprocessor608.User interface620 allows a user (not shown) to operatesystem600, and to set the characteristics ofsystem600 for a given operation scenario.
• Power supply602 provides electrical power tofiber laser604,hardware controller606 andprocessor608.Fiber laser604 generates a pulsed beam of light, which is provided totransceiver optics610.Transceiver optics610 transmits the pulsed beam of light toscanner614.
• INS618 continuously detects the motion of the vehicle (i.e., the position and the orientation), on whichsystem600 is mounted, in real-time, and provides this information toprocessor608.Processor608 uses the position and orientation information to instructhardware controller606 to setscanner driver616 to the appropriate mode of operation.Scanner driver616 can be set to different modes of operation depending on the detected motion of the vehicle, as was depicted inFIGS. 8A,8B,8C,8D,8E,8F and8G.Hardware controller606sets scanner driver616 to a required mode of operation.Scanner driver616 then mechanically sets the mode of operation ofscanner614, which will scan a volume of interest in front ofLADAR system600. The pulsed beam of light, which is provided toscanner614 bytransceiver optics610, is then emitted as an output pulsed beam oflight626, towards the volume of interest ofsystem600.Hardware controller606 can also setscanner614 to scan a volume of interest which is located at a predetermined distance in front ofLADAR system600. For example,processor608 can predict, based on the data regarding the motion (e.g., speed, heading, altitude and the like) ofLADAR system600 provided byINS618, the location ofLADAR system600 in 10 seconds. Using this location prediction,hardware controller606 can setscanner614 to scan the volume of interest whichLADAR system600 will encounter in 10 seconds, and not the volume of interest it is currently encountering.
• Processor608 also uses the position and orientation information, detected byINS618, to instructhardware controller606 to setfiber laser604 to a particular mode of operation.Fiber laser604 can operate in a number of modes of operation, depending on the change in motion of the vehicle, as was depicted inFIGS. 6A and 6B.
• Pulsedlight beam626 is reflected off of an object (not shown), in the scanned volume of interest ofsystem600, as a reflected pulsedlight beam628. Reflected pulsedlight beam628 is detected byoptical receiver612 viascanner614 andtransceiver optics610.Optical receiver612 provideshardware controller606 with information indicative of the characteristics of reflected pulsedlight beam628.Hardware controller606 then setsfiber laser604 to a particular mode of operation, according to the characteristics of reflected pulsedlight beam628.
• The characteristics of reflected pulsedlight beam628 may indicate that the object, from which reflected pulsedlight beam628 was reflected from, is an obstacle presenting a possible hazard to the vehicle. In this case,hardware controller606 providesprocessor608 with information regarding a possible hazard to the vehicle.Processor608 then setsHMD symbol generator622 andvoice management unit624 to an appropriate mode of operation to convey this information to the user.
• HMD symbol generator622 indicates the presence of a possibly hazardous obstacle, in the path of the vehicle, to a vehicle operator (not shown) through a visual effect.Voice management unit624 indicates the presence of a possibly hazardous obstacle, in the path of the vehicle, to the vehicle operator through an acoustic effect (e.g. a beeping sound, a human voice, and the like).HMD symbol generator622 andvoice management unit624 can also provide the vehicle operator with information regarding the location and the nature (e.g. the size and type of obstacle) of the possibly hazardous obstacle, as received byprocessor608.
• The GPS detects the position of the vehicle in a given coordinate system and the altimeter detects the height of the vehicle. The detected position and height of the vehicle are provided toprocessor608.Processor608 uses the detected position and height of the vehicle to increase the accuracy of the detected motion of the vehicle detected byINS618. The weight sensor detects the weight on the wheels of the vehicle, and provides the detected weight toprocessor608.Processor608 uses the detected weight to determine if the vehicle is on the ground or if the vehicle is airborne (i.e., the flight state of the vehicle). The detected weight is used byprocessor608 to increase the operational safety offiber laser604 by preventing the use of fiber laser604 (e.g., by not sending power to fiber laser604) unless the vehicle is airborne. It is noted that the altimeter and the weight sensor are generally used when the vehicle is an airborne vehicle.
• Reference is now made toFIG. 12, which is a schematic illustration of a method for wire detection, operative in accordance with a further embodiment of the disclosed technique.FIG. 12 also illustrates a method for preventing receiver burn-out in a LORD system. Inprocedure650, a low energy pulsed beam of light is transmitted to a volume of interest to detect objects, for example, to detect telephone wires hanging between posts. With reference toFIG. 3C,system240 first transmits low energy pulsed beam oflight246, and waits to see ifreceiver244 receives a reflection from objects in the volume of interest in front ofsystem240.
• Inprocedure652, a reflection of the low energy pulsed beam of light is detected within a predetermined amount of time. If the transmitted low energy pulsed beam of light impinges upon an object having high reflectance in the volume of interest, then a reflected low energy pulsed beam of light will be received and the method returns toprocedure650. Reflections from objects having high reflectance beyond the volume of interest will also be received, although such reflections may be of very low energy due to the distance over which the reflections must travel. If the transmitted low energy pulsed beam of light does not impinge upon an object having high reflectance in the volume of interest, but upon another object, then a reflected low energy pulsed beam of light will not be received, as the reflected low energy pulsed beam of light will dissipate before it is received, and the method then proceeds toprocedure654.
• With reference toFIG. 3C,system240 first transmits low energy pulsed beam oflight246, and waits to see ifreceiver244 receives a reflection from objects in the volume of interest in front ofsystem240. When low energy pulsed beam oflight246 is reflected frompower lines252, a pulsed beam of light254 (dotted arrows) is reflected back towardsreceiver244. Sincepower lines252 are very thin and are not highly reflective objects, pulsed beam oflight254 is significantly lower in energy than low energy pulsed beam oflight246. In fact, pulsed beam oflight254 is so low in energy that it dissipates before it is received byreceiver244.
• Inprocedure654, if the reflected low energy pulsed beam of light is not received, after a predetermined amount of time, ranging from a few microseconds to hundreds of microseconds, or if the energy level of the received reflected pulsed beam of light does not exceed a predetermined threshold, then a high energy pulsed beam of light is transmitted to the volume of interest. After the high energy beam of light is transmitted, the method returns toprocedure650, where a low energy pulsed beam of light is transmitted. With reference toFIG. 3C, after a waiting period, ranging from a few microseconds to hundreds of microseconds, ifreceiver244 does not receive pulsed beam of light254 (which it will not, from hard-to-see objects), or if the energy level of a reflected pulsed beam of light does not exceed a predetermined threshold, thenfiber laser242 sends out high energy pulsed beam oflight248.
• According to the method ofFIG. 12, hard-to-see objects in a volume of interest can be detected by high energy pulsed beams of light, with no risk of burning out the receivers in a LORD system, since a low energy pulsed beam of light is initially transmitted to a volume of interest to verify if any objects having high reflectance, such as retro-reflectors are present in the volume of interest. If objects having high reflectance are present, then the high energy pulsed beam of light is not transmitted, thereby preventing receiver burn-out. If objects having high reflectance are not present, then the high energy pulsed beam of light is transmitted, thereby allowing hard-to-see objects, such as telephone wires, to be detected.
• It is noted that even if the high energy pulsed beam of light reflects from an object having high reflectance that is located beyond the volume of interest, then the receivers of the LORD system will also not burn-out, as the reflected pulsed beam of light will be of low energy if it reflected from a distance that is larger than the volume of interest. As mentioned above, with reference toFIG. 3C, in general, the volume of interest is defined as a volume beyond which even high energy pulsed beams of light reflecting from objects having high reflectance will impinge upon a receiver as low energy pulsed beams of light.
• Reference is now made toFIG. 13, which is a schematic illustration of a method, operative in accordance with another embodiment of the disclosed technique. Inprocedure680, a volume of interest is scanned from a moving vehicle, using a pulsed beam of light, at a certain PRR and at a certain output peak power. The volume of interest is scanned with a LORD system. With reference toFIG. 5A,system320 is a LORD system, mounted on a vehicle.Fiber laser324 scans a volume of interest in front ofsystem320 using pulsed beams of light to detect obstacles, and in particular hard-to-see obstacles, which may be in the volume of interest.
• Inprocedure682, the motion of the vehicle is detected. It is noted that the motion of the vehicle refers to the angular velocity and the angular acceleration and to the linear velocity (i.e., the speed) and the linear acceleration of the vehicle, as well as whether the vehicle is moving in a straight direction or whether the vehicle is turning, and the rate of change in the direction of motion of the vehicle. With reference toFIG. 5A,motion detector326 constantly detects the motion ofvehicle322, and provides a signal tocontroller325 indicative of the changes in motion ofvehicle322.
• In an alternative toprocedure682, if the LORD system is attached to a gimbals, where it is free to move in a plurality of directions, then the motion of the LORD system is detected with respect to the vehicle. With reference toFIG. 5A, in the embodiment wherefiber laser324 is attached to the gimbals,motion detector326 detects and determines the motion ofvehicle322 as well as the motion offiber laser324 with respect tovehicle322.
• Inprocedure684, the PRR of the pulsed beams of light is adjusted according to the detected angular motion of the vehicle using a decreasing function. In general, the PRR is a function of the angular velocity alone, although the angular acceleration can also be factored into the function in order to correct for errors in the adjustments of the PRR according to changes in the detected angular velocity, as is known in the art. The PRR of the pulsed beams of light is adjusted according to the detected angular motion in order to maintain the scan density of the pulsed beams of light and to provide an operator with information about obstacles in front of her with enough time for her to avoid them. The angular motion of the vehicle can include either the angular velocity of the vehicle, the angular acceleration of the vehicle, or both). For example, if the vehicle is traveling in a straight direction (i.e., no angular velocity, such that the rate of change of motion of the vehicle is equal to zero), then the PRR of the pulsed beam of light is increased, and is set to be high. The PRR is increased because the flight path of the moving vehicle is less predictable when the vehicle is traveling in a straight direction. As described above inFIG. 8D, since the flight path of the moving vehicle is less predictable when the vehicle is traveling in a straight direction, the FOV of the scan is increased. By increasing the FOV of the scan, the PRR needs to be increased in order to maintain the scan density of the pulsed beams of light. As mentioned above, maintaining the scan density is at the discretion of the operator of the vehicle.
• If the vehicle is not moving in a straight path, but rather in a curved path, since the direction of travel of the vehicle is constantly changing (i.e., the angular velocity of the vehicle is high), the PRR of the pulsed beam of light is decreased. Since the LOS of the LORD system is changing in a particular direction, there is more predictability in terms of where the vehicle is heading, and as such the PRR is decreased because an operator of the vehicle only needs to see obstacles in front of her that are directly in her changing LOS. As mentioned above inFIG. 8E, since the flight path of the vehicle is more predictable, the FOV of the scan can be reduced. By reducing the FOV of the scan, the PRR can be reduced to maintain the scan density of the pulsed beams of light. Therefore, as at least one of the angular velocity and angular acceleration of the vehicle increases, the PRR of the pulsed beams of light is decreased using a decreasing function, and as at least one of the angular velocity and angular acceleration of the vehicle decreases, the PRR of the pulsed beams of light is increased.
• With reference toFIG. 5A, in order to increase the energy efficiency ofsystem320, and to provide an operator with information about obstacles in front of her with enough time for her to avoid them,controller325 adjusts the PRR of the pulsed beams of light transmitted byfiber laser324 according to the detected angular motion of the vehicle. With reference toFIG. 6B, the PRR of fiber laser324 (FIG. 5A) is increased as the angular velocity ofhelicopter350 decreases, since the flight path ofhelicopter350 will be more uncertain in a given time period than when traveling at higher angular velocities. At high angular velocities, the probability of the pilot being in need of information regarding obstacles located outside the flight path is decreased, for example inhelicopter356, since a curved flight path is more predictable of the current general motion of the helicopter than a straight flight path. In this case, the PRR offiber laser324 is decreased.
• In an alternative toprocedure684, if the LORD system is attached to a gimbals, then the PRR of the pulsed beams of light is adjusted according to the detected angular motion of the LORD system, in order to increase the energy efficiency of the LORD system and to provide an operator with information about obstacles in front of her with enough time for her to avoid them. With respect toFIG. 5A, in the embodiment wherefiber laser324 is attached to a gimbals, the change in PRR of the pulsed beam of light is a function of the degree to which the direction offiber laser324 changes with respect tovehicle322.
• Inprocedure686, the output peak power of the pulsed beams of light is adjusted according to the detected linear motion of the vehicle using an increasing function. For example, if the vehicle is traveling in a straight direction at high speeds, the output peak power of the pulsed beam of light is increased, since the vehicle will be covering more distance per unit time. At higher speeds, an increase in the output peak power is needed such that objects which are much farther in front of the vehicle can be detected, such as objects located a few hundred meters, or a few kilometers in front of the vehicle. At higher speeds, the reaction time of the operator is reduced, therefore, an increase in the output peak power of the pulsed beam of light is needed to increase the distance from which objects can be seen by the operator. By increasing the distance from which objects can be seen, the reduced reaction time of the operator can be compensated for.
• If the vehicle is moving in a straight direction at low speeds since less distance will be covered per unit time, the output peak power of the pulsed beam of light is decreased, since the operator of the vehicle only needs information about obstacles that are relatively nearby. At lower speeds, the reaction time of the operator is increased, and as such, the output peak power of the pulsed beam of light can be reduced. Therefore, as at least one of the linear velocity and linear acceleration of the vehicle increases, the output peak power of the pulsed beams of light is also increased, and as at least one of the linear velocity and linear acceleration of the vehicle decreases, the output peak power of the pulsed beams of light is also decreased. With reference toFIG. 5A, whenvehicle322 is traveling in a straight direction at high speeds, the output peak power offiber laser324 is increased bycontroller325 so as to provide an increase in the detection range in front ofvehicle322 ofsystem320. And likewise, whenvehicle322 is traveling in a straight direction at low speeds, the output peak power offiber laser324 is decreased bycontroller325 so as to provide a decrease in the detection range in front ofvehicle322 ofsystem320.
• With reference toFIG. 6A, since the pilot needs information about obstacles that are much farther in front of her, becausehelicopter340 is traveling in a straight direction at high speeds, the output peak power of fiber laser324 (FIG. 5A) is increased by controller325 (FIG. 5A), thereby increasing the detection range ofsystem320. Also, in the case wherehelicopter345 is traveling in a straight direction at low speeds, since the pilot needs information about obstacles that are relatively nearby, becausehelicopter345 does not cover that much distance per unit time, and the reaction time of the pilot is increased, the output peak power of fiber laser324 (FIG. 5A) is reduced bycontroller325. This reduction in output peak power is executed because increasing the detection range ofsystem320 does not give the pilot anymore useful information about obstacles in front of her since the vehicle is not covering significant distance per unit time.
• In an alternative toprocedure686, if the LORD system is attached to a gimbals, then the output peak power of the pulsed beams of light is adjusted according to the detected linear motion of the LORD system. With respect toFIG. 5A, in the embodiment wherefiber laser324 is attached to a gimbals, the change in output peak power of the pulsed beam of light is a function of the degree to which the linear velocity offiber laser324 changes with respect tovehicle322.
• Inprocedure688, the PRR of the pulsed beams of light is adjusted according to the detected linear motion of the vehicle, using an increasing function, in order to increase the energy efficiency of the LORD system and to provide an operator with information about obstacles in front of her with enough time for her to avoid them. Furthermore, the PRR of the pulsed beams of light is adjusted to maintain the scan density of the pulsed beams of light. The linear motion of the vehicle can include the linear velocity of the vehicle, the linear acceleration of the vehicle or both. For example, if the vehicle is traveling at low speeds, then the PRR of the pulsed beam of light is reduced, and is set to be low. At low speeds, the probability of the pilot being in need of information regarding obstacles located farther in her LOS (hence a decrease in the PRR of fiber laser324) is decreased since she will be approaching them at a decreased rate. Also, as described above inFIG. 8B, at lower speeds, the FOV of the scan is reduced. As such, in order to maintain the scan density of the pulsed beams of light, the PRR is reduced as well. Furthermore, since lesser distances are being traversed, a less rapid rate of pulses needs to be transmitted to maintain the quality of the received image. Also, at low speeds, the most significant obstacles to the vehicle will lie directly in the LOS of the operator.
• If the vehicle is moving at high speeds, since the vehicle will traverse distances quicker, the PRR of the pulsed beam of light is increased. At high speeds, the probability of the pilot being in need of information regarding obstacles located further in her LOS (hence an increase in the PRR of fiber laser324) in increased since she will be approaching them at an increased rate. As described above inFIG. 8C, at higher speeds, the FOV of the scan is increased. As such, in order to maintain the scan density of the pulsed beams of light, the PRR is increased as well. Furthermore, since greater distances are being traversed, a more rapid rate of pulses needs to be transmitted (i.e., the scan density of the pulses needs to be increased) to maintain the quality of the received image. Therefore, as the speed of the vehicle increases, the PRR of the pulsed beams of light is increased, according to an increasing function, and as the speed of the vehicle decreases, the PRR of the pulsed beams of light is decreased. It is noted that the change in PRR according to the linear motion of the vehicle is at the discretion of the operator, since situations may arise where the operator may not want to maintain a constant scan density (and therefore a constant image quality).
• With reference toFIG. 5A, in order to increase the energy efficiency ofsystem320, and to provide an operator with information about obstacles in front of her with enough time for her to avoid them,controller325 adjusts the PRR of the pulsed beams of light transmitted byfiber laser324 according to the detected linear motion of the vehicle. With reference toFIG. 6A, ifhelicopter340 travels in a straight direction at low speeds, which narrows the field of interest to the pilot, since less distance is covered per unit time, then controller325 (FIG. 5A) decreases the PRR of fiber laser324 (FIG. 5A). The decrease in the PRR is also a result of a decrease in the FOV of the scan of fiber laser324 (not shown). Ifhelicopter346 travels in a straight direction at high speeds, which widens the field of interest to the pilot, since more distance is covered per unit time, thencontroller325 increases the PRR offiber laser324. The increase in the PRR is also a result of an increase in the FOV of the scan of fiber laser324 (not shown).
• Reference is now made toFIG. 14, which is a schematic illustration of a method, operative in accordance with a further embodiment of the disclosed technique. Inprocedure700, a volume of interest is scanned, from a moving vehicle, using a pulsed beam of light. It is noted that the scan has a certain FOV, and that the pulsed beam of light is at a certain LOS. With reference toFIG. 7,system380 is a LORD system.Fiber laser384 scans a volume of interest in front ofsystem380 using pulsed beams of light to detect obstacles, and in particular hard-to-see obstacles, which may be in the volume of interest.
• Inprocedure702, the motion of the vehicle is detected. It is noted that the vehicle is mounted with a LORD system. With reference toFIG. 7,motion detector386 constantly detects the motion ofvehicle382, and provides a signal tocontroller385 indicative of the changes in the motion ofvehicle382. For example,motion detector386 can provide an indication tocontroller385 thatvehicle382 is moving at a particular linear velocity and linear acceleration and at a particular angular velocity and angular acceleration.
• Inprocedure704, the FOV of the scan, (i.e., the width of the FOV in the vehicle plane) is adjusted according to the detected angular motion of the vehicle using a decreasing function. The angular motion of the vehicle can include the angular velocity of the vehicle, the angular acceleration of the vehicle, or both. For example, as the vehicle increases in angular velocity, the FOV of the scan of the LORD system is decreased. Since the vehicle is traveling at higher angular speeds, thereby resulting in a more predictable flight path, the FOV of the LORD system is decreased so that only the most significant volume of interest (i.e., the predicted flight path of the vehicle), is scanned. As the vehicle decreases in angular speed, the FOV of the scan of the LORD system is increased, thereby increasing the range of the scan of the LORD system. Since the vehicle is traveling at slower angular speeds, thereby resulting in a less predictable flight path for the vehicle, the FOV of the scan of the LORD system is increased so that a larger volume of interest, where obstacles to the vehicle can be found, is scanned.
• With reference toFIG. 8D, ashelicopter430 decreases in angular speed, thespread angle429 of the FOV of system380 (FIG. 7) is increased by controller385 (FIG. 7), thereby increasing arange431 of the width of the spread angle of the FOV ofsystem380. With reference toFIG. 8E, ashelicopter435 increases in angular speed, thespread angle436 of the FOV ofsystem380 is increased bycontroller385, thereby increasing arange438 of the width of the spread angle of the FOV ofsystem380.
• Inprocedure706, the LOS of the scan is adjusted according to the detected angular motion of the vehicle using an increasing function. The angular motion of the vehicle can include the angular velocity of the vehicle, the angular acceleration of the vehicle, or both. For example, as at least one of the angular velocity and the angular acceleration of the vehicle increases (i.e., the vehicle travels in a more curved direction), the angle through which the LOS of the scan is adjusted is increased. By adjusting the LOS of the scan of the FOV of the vehicle according to the angular motion of the vehicle, a pilot can get an image of the location where the vehicle will be in a certain amount of time. As the angular motion increases, the visibility of the pilot is decreased, since the LOS of the vehicle will be changing at an increased rate. In order to increase the visibility of the pilot, an initial LOS (e.g., the LOS of the scan when the vehicle has no angular velocity) of the scan is adjusted in the direction of motion of the vehicle to a final LOS of the scan (e.g., the LOS of the scan when the vehicle has a particular angular velocity). As the angular motion increases, the angle between the initial LOS of the scan and the final LOS of the scan is increased. As the angular motion increases, since the LOS of the LORD system will be constantly changing, the LOS of the scan is adjusted in the direction of motion of the LORD system through an increased angle such that the pilot will be provided with up-to-date information regarding potential obstacles in her flight path. As at least one of the angular velocity and angular acceleration of the vehicle decreases (i.e., as the vehicle travels in a more straight direction), the angle through which the LOS of the scan of the LORD system is moved in the direction of motion is decreased. Since the LOS of the LORD system will be changing at a decreased rate, the angle through which the LOS of the scan is adjusted in the direction of motion of the vehicle is also decreased.
• With reference toFIG. 8F, ashelicopter441 decreases in angular velocity (i.e., a light turn), aninitial FOV444, with the LOS of the scan being represented by an arrow443_A, is adjusted in the direction of motion ofhelicopter441, to afinal FOV445. With reference toFIG. 8G, as the angular velocity ofhelicopter453 begins to increase, the angle through which the LOS of the scan is moved in, following the change in orientation ofhelicopter453, also increases. As the angular velocity ofhelicopter453 decreases, the angle through which the LOS of the scan is moved in also decreases.
• Inprocedure708, the FOV of the scan is adjusted according to the detected linear motion of the vehicle using an increasing function. The detected linear motion can include at least one of the linear velocity of the vehicle and the linear acceleration of the vehicle. For example, as the vehicle decreases in linear velocity, the FOV of the scan is decreased since less distance will be covered by the vehicle and since the pilot will have more time to react. As less distance will be covered and the reaction time is increased, only the most significant volume of interest is scanned, thereby conserving energy. At low linear speeds, this significant volume of interest lies directly in the LOS of the vehicle. As the vehicle increases in linear velocity, the FOV of the scan is increased, since more distance will be covered by the vehicle and since the pilot will have less time to react.
• With reference toFIG. 8B, ashelicopter410 decreases in speed, aspread angle417 of the FOV ofsystem380 is decreased by controller385 (FIG. 7), thereby decreasing a range412 of the width of the spread angle of the FOV of system380 (FIG. 7). Sincehelicopter410 is traveling at slower speeds, thereby resulting in less of a need forsystem380 to scan a large FOV (since less distance is covered and the time in which the pilot can react, i.e., the look ahead distance, is increased), the FOV ofsystem380 is decreased so that only the most significant volume of interest, where obstacles to helicopter410 can be found, is scanned. This significant volume of interest lies directly in the LOS ofhelicopter410 at low speeds. With reference toFIG. 8C, ashelicopter420 increases in speed, aspread angle427 of the FOV ofsystem380 is increased bycontroller385, thereby increasing arange422 of the width of the spread angle of the FOV ofsystem380. Sincehelicopter420 is traveling at higher speeds (since more distance is covered and the time in which the pilot can react, i.e., the look ahead distance, is decreased), thereby resulting in more of a need forsystem380 to scan a larger FOV, the FOV ofsystem380 is increased so that a larger volume of interest, where obstacles to helicopter420 can be found, is scanned.
• It is noted that inprocedure704, in general, the FOV of the scan is adjusted according to the angular velocity. The angular acceleration can be used to correct for errors in the adjustment of the FOV of the scan according to the angular velocity, as is known in the art. Also, inprocedures706 and708, the LOS of the scan, and the FOV of the scan, are each respectfully adjusted according to the linear velocity. In each of these procedures, the linear acceleration can be used to correct for errors in the adjustment of, respectfully, the LOS of the scan and the FOV of the scan, according to the linear velocity, as is known in the art.
• It will be appreciated by persons skilled in the art that the disclosed technique is not limited to what has been particularly shown and described hereinabove. Rather the scope of the disclosed technique is defined only by the claims, which follow.

Claims (21)

1.-67. (canceled)

68. Method, for detecting at least one object, comprising the procedures of:

scanning a volume of interest, from a moving vehicle, using a pulsed beam of light at a certain field-of-view (FOV);

detecting the motion of said vehicle;

adjusting said FOV according to detected motion of said vehicle.

69. The method according toclaim 68, wherein said procedure of adjusting comprises adjusting said FOV according to a detected linear velocity of said vehicle using an increasing function.

70. The method according toclaim 68, wherein said procedure of adjusting comprises adjusting said FOV according to a detected angular velocity of said vehicle using a decreasing function.

71. The method according toclaim 68, wherein said detected motion is selected from the list consisting of:

the angular velocity of said vehicle;

the angular acceleration of said vehicle;

the linear velocity of said vehicle; and

the linear acceleration of said vehicle.

72. The method according toclaim 68, wherein said pulsed beam of light is at a certain line-of-sight (LOS), further comprising the procedure of adjusting said LOS in the direction of said motion according to a detected angular velocity of said vehicle using an increasing function.

73. The method according toclaim 68, wherein said pulsed beam of light is at a certain pulse repetition rate (PRR), and wherein said pulsed beam of light originates from a light source, further comprising the procedure of adjusting said PRR of said pulsed beam of light according to said detected motion.

74. The method according toclaim 73, wherein said procedure of adjusting comprises adjusting said PRR according to a detected linear velocity of said vehicle using an increasing function.

75. The method according toclaim 73, wherein said procedure of adjusting comprises adjusting said PRR according to a detected angular velocity of said vehicle using a decreasing function.

76. The method according toclaim 73, further comprising the procedures of:

detecting the motion of said light source with respect to said vehicle;

adjusting the PRR of said pulsed beam of light according to said detected motion.

77. The method according toclaim 76, wherein said procedure of adjusting comprises adjusting said PRR according to a detected linear velocity of said light source with respect to said vehicle using an increasing function.

78. The method according toclaim 76, wherein said procedure of adjusting comprises adjusting said PRR according to a detected angular velocity of said light source with respect to said vehicle using a decreasing function.

79. The method according toclaim 68, wherein said pulsed beam of light is at a certain output peak power and wherein said pulsed beam of light originates from a light source, further comprising the procedure of adjusting said output peak power of said pulsed beam of light according to said detected motion.

80. The method according toclaim 79, wherein said procedure of adjusting comprises adjusting said output peak power according to a detected linear velocity of said vehicle using an increasing function.

81. The method according toclaim 79, further comprising the procedures of:

detecting the motion of said light source with respect to said vehicle;

adjusting said output peak power of said pulsed beam of light according to a detected motion of said light source.

82. The method according toclaim 81, wherein said procedure of adjusting comprises adjusting said output peak power according to a detected linear velocity of said light source with respect to said vehicle using an increasing function.

83.-84. (canceled)

85. The method according toclaim 68, further comprising the procedures of:

providing an indication to a user, said indication being related to said at least one object; and

adjusting said indication to said user according to said detected motion of said vehicle.

86. The method according toclaim 68, further comprising the procedures of:

determining an updated location of said at least one object; and

presenting said updated location to a user.

87. The method according toclaim 86, wherein said procedure of presenting comprises selectively presenting said updated location to said user in accordance with a nature of said at least one object.

88. The method according toclaim 86, wherein said procedure of presenting comprises presenting said updated location to said user only when said at least one object is a possibly hazardous obstacle to said vehicle.

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