Disclosure of Invention
Therefore, it is necessary to provide a laser radar system for solving the problems of high cost, low measurement accuracy and poor interference resistance in the conventional Flash radar.
The present invention provides a laser radar system comprising:
the emitting module is used for generating and emitting an emitting laser signal of the amplitude-modulated continuous wave;
the emission optical system is used for carrying out beam splitting processing on the emergent laser signal so that the emergent laser signal subjected to beam splitting processing uniformly illuminates the whole detection area; and
the detection module is used for reflecting the laser signal and converting the reflected laser signal into a reflected electrical signal, wherein the reflected laser signal is a laser signal generated by reflecting the emergent laser signal by an object in a detection area; and
and the signal processing module is used for receiving the reflected electric signal, acquiring the phase offset of the emergent laser signal and the reflected laser signal according to the reflected electric signal, and calculating the absolute distance of the object in the detection area according to the phase offset.
In one embodiment, the transmitting module comprises:
the laser is used for emitting laser beams with preset wavelengths;
the amplitude modulator is used for modulating the laser beam with the set wavelength by utilizing a carrier signal so as to generate the emergent laser signal; and
and the collimating lens is used for collimating the emergent laser signal.
In one embodiment, the emission optical system comprises a Dammann grating, and the emergent laser beams are diffracted by the Dammann grating to form a laser beam array comprising a plurality of emergent laser sub-beams with equal light intensity.
In one embodiment, the lidar system further comprises a receiving optical system, wherein the receiving optical system is used for receiving the reflected laser signal and carrying out convergence and shaping processing on the reflected laser signal so as to adapt the spot size of the reflected laser signal to the receiving surface size of the detection module
In one embodiment, the receiving optical system includes a focusing mirror for converging the reflected laser signal and a shaping mirror for shaping the converged reflected laser signal
In one embodiment, the detection module includes a detector array including a plurality of detectors, the spot distribution of the outgoing laser light in the far field after being split by the emission optical system is consistent with the number of the detectors, and one of the detectors receives the reflected laser signal corresponding to one of the spots and converts the reflected laser signal into the reflected electrical signal.
In one embodiment, the detector is an avalanche photodiode
In one embodiment, the detection module further includes a filter array, the filter array includes a plurality of filters, the filters correspond to the detectors one to one, and the filters are configured to filter the reflected electrical signal, obtain the filtered reflected electrical signal, and send the filtered reflected electrical signal to the signal processing module.
In one embodiment, the detection module further includes a filter array, and the filter array is electrically connected to the detection module and the signal processing module, and is configured to perform filtering processing on the reflected electrical signal, obtain a filtered reflected electrical signal, and send the filtered reflected electrical signal to the signal processing module.
In one embodiment, the filter is a passive filter.
In one embodiment, the phase shift is related to the absolute distance of the object in the detection area by
Wherein d is an absolute distance of an object within the detection area, c is a speed of light, and f is a modulation frequency of the outgoing laser signal,is the phase offset.
According to the laser radar system, the outgoing laser signals emitted to the detection area are subjected to beam splitting processing through the emission optical system, so that the outgoing laser signals subjected to beam splitting processing uniformly illuminate the whole detection area, the light energy of each detection direction is concentrated after beam splitting, a farther detection distance can be reached, the crosstalk problem among channels in all directions cannot be caused by echoes, interference light signals in the reflected laser signals are reduced, the signal to noise ratio of the reflected electric signals is improved, and the measurement precision and the imaging quality are improved. Secondly, the absolute distance of the object in the detection area is calculated according to the phase offset, and compared with the method of directly measuring the flight time, the method is easier to realize, and the complexity of a back-end circuit is reduced, so that the generation cost is reduced. In addition, the modulation of the outgoing laser signal of the amplitude-modulated continuous wave signal is opposite to pulse modulation, so that the fixed deviation caused by ambient light is eliminated, and the measurement precision is improved.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, but rather should be construed as broadly as the present invention is capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Referring to fig. 1 and fig. 2 together, an embodiment of the present invention provides a lidar system including a transmitting module 100, a transmitting optical system 200, a detecting module 300, and a data processing module 400.
The emitting module 100 is configured to generate and emit an emission laser signal of an Amplitude Modulated Continuous Wave (AMCW).
The emission optical system 200 is configured to perform beam splitting processing on the outgoing laser signal, so that the outgoing laser signal subjected to beam splitting processing uniformly illuminates the entire detection area.
The detection module 300 is configured to receive the reflected laser signal, and convert the reflected laser signal into a reflected electrical signal, where the reflected laser signal is a laser signal generated by reflecting the outgoing laser signal by an object in a detection area.
The signal processing module 400 is configured to receive the reflected electrical signal, obtain a phase offset between the outgoing laser signal and the reflected laser signal according to the reflected electrical signal, and calculate an absolute distance of an object in the detection area according to the phase offset.
It can be understood that the outgoing laser signal emitted to the detection area is subjected to beam splitting processing by the emission optical system 200, so that the outgoing laser signal subjected to beam splitting processing uniformly illuminates the whole detection area, the light energy in each detection direction is concentrated after beam splitting, a farther detection distance can be reached, the crosstalk problem among channels in each direction cannot be generated by an echo, interference light signals in the reflected laser signal are reduced, the signal-to-noise ratio of the reflected electric signal is improved, and the measurement precision and the imaging quality are improved. Secondly, the absolute distance of the object in the detection area is calculated according to the phase offset, and compared with the method of directly measuring the flight time, the method is easier to realize, and the complexity of a back-end circuit is reduced, so that the generation cost is reduced. In addition, the modulation of the outgoing laser signal of the amplitude-modulated continuous wave signal is opposite to pulse modulation, so that the fixed deviation caused by ambient light is eliminated, and the measurement precision is improved.
In one embodiment, the transmitting module 100 includes a laser 110, an amplitude modulator 120, and a collimating mirror 130.
The laser 110 is used for emitting a laser beam with a preset wavelength. In this embodiment, since the operating principle of the radar system is based on the AMCW mechanism, the transmitting light source does not need to use a frequency modulation laser, and only the selected light source with a specific wavelength needs to have a proper line width. Therefore, there may be used, but not limited to, Distributed Feedback lasers (DFB lasers), Laser Diodes (LDs), fiber lasers, Vertical Cavity Surface Emitting Lasers (VCSELs), and the like.
The amplitude modulator 120 modulates the laser beam with the set wavelength by using a carrier signal to generate the outgoing laser signal.
It is understood that the amplitude modulator 120 linearly modulates the laser beam with the preset wavelength by using a carrier signal to emit the outgoing laser signal. It should be noted that, in the modulation process, the frequency of the laser beam with the preset wavelength is not changed, but the carrier thereof, that is, the carrier signal is modulated, and the frequency of the carrier signal is much smaller than the frequency of the laser beam with the preset wavelength, so that the modulation is easier to implement, and the modulation difficulty is reduced.
In this embodiment, the amplitude modulator 120 is a dual parallel phase modulator. The microwave photon link of the double parallel phase modulators adopts 2 phase modulators, and the phase offset difference of the amplitude modulator is adjusted to pi, so that 2 paths of phase modulation signals cannot be mutually offset when the beat frequency of a receiving end is achieved, and the direct detection of the phase modulation of the microwave signals is realized. Furthermore, the output optical frequency can be changed by mechanically changing the resonator length. The modulation method of the laser source is not particularly limited in this embodiment, as long as the light source can output linear continuous light.
The collimating lens 130 is disposed coaxially with the emitting module 100, and is configured to collimate the outgoing laser signal. In this embodiment, the collimating lens 130 for maintaining the collimation of the outgoing laser signal is a transmissive collimating lens, and a zinc selenide lens is generally used as the transmissive collimating lens. After being collimated by the collimator lens, the outgoing laser signal is split by the emission optical system 200 and then is incident on an object in the detection area.
In one embodiment, the emission optical system 200 includes a Dammann grating, and the outgoing laser beams are diffracted by the Dammann grating to form a laser beam array including a plurality of outgoing laser sub-beams having equal intensities.
It can be understood that the Dammann grating can not only split the incident emergent laser signal to form a laser beam array containing a plurality of emergent laser sub-beams with equal light intensity, so that the emergent laser signal uniformly illuminates the whole detection area, but also can keep the same property as the original incident light, reduce the attenuation of space capacity, and is beneficial to improving the problem that the traditional flash radar has a short detection distance due to the emergent spherical wave (energy attenuation characteristic). In addition, the light spots of the detection light split by the Dammann grating are separated in a far field, so that information can be collected in each light spot direction, and crosstalk among channels is reduced. It should be noted that the beam splitting number of the dammann grating and the number of detectors receiving the reflected laser signals should be consistent, and the far field light spot distribution of the dammann grating and the distribution of the detectors should be consistent.
In one embodiment, the lidar system further comprises a receiving optical system 500, and the receiving optical system 500 is configured to receive the reflected laser signal, and perform convergence and shaping processing on the reflected laser signal to adapt the size of the spot of the reflected laser signal to the size of the receiving surface of the detection module 300.
In one embodiment, the receiving optical system 500 includes a focusing mirror 510 and a shaping mirror 520, the focusing mirror 510 is used for converging the reflected laser signal, and the shaping mirror 520 is used for shaping the converged reflected laser signal. In this embodiment, the focusing mirror 510 converges the reflected laser signal, and the converged reflected laser signal is shaped by the shaping mirror 520, so that the spot size of the reflected laser signal is adapted to the size of the receiving surface of the detection module 300, and the reflected laser signal directly irradiates the surface of the receiving module in the form of an approximate plane wave, so as to eliminate the difference of pixel points caused by different detection areas and different illumination intensities, thereby improving the imaging quality.
In one embodiment, the detection module 300 includes a detector array 310, the detector array 310 includes a plurality of detectors, the spot distribution of the outgoing laser light in the far field after being split by the emission optical system 200 corresponds to the number of the detectors, and one of the detectors receives the reflected laser light signal corresponding to one of the spots and converts the reflected laser light signal into a reflected electrical signal.
In this embodiment, the number of the beams of the dammann grating is equal to the number of the detectors, that is, the light spot distribution of the dammann grating at the far field is equal to the number of the detectors, and one detector receives a reflected laser signal formed by one light spot, so that the problem of crosstalk between channels in each direction generated by the reflected laser signal is avoided, and interference optical signals in the reflected laser signal are reduced.
In one embodiment, the detector is an Avalanche Photodiode (APD). In this embodiment, the avalanche photodiode may also be used to amplify the reflected electrical signal, so as to improve the sensitivity of detection. The detector may also be a charge coupled device or a complementary metal oxide semiconductor sensor. The charge coupled device, the avalanche photodiode and the complementary metal oxide semiconductor sensor all have the function of converting an optical signal into a reflected electrical signal, so that the reflected laser signal can be converted into the reflected electrical signal by using the charge coupled device, the avalanche photodiode and the complementary metal oxide semiconductor sensor as detectors. In addition, other devices having a function of converting an optical signal into a reflected electrical signal may be used as the detector, and the implementation of the detector is not specifically limited in the present invention
In one embodiment, the detection module 300 further comprises a real-time processing system 330, wherein the real-time processing system 330 is electrically connected to the detector array 310 and provides a reverse bias voltage to the detector array 310 to control the operation of the detector array 310. In this embodiment, the real-time processing system applies a reverse bias to the avalanche photodiode to control the operating state of the avalanche photodiode, so as to ensure that the determination output of the avalanche photodiode and the reception of a new pulse are performed synchronously.
In one embodiment, the detection module 300 further includes a filter array 320, where the filter array 320 includes a plurality of filters, and the filters correspond to the detectors one to one, and are configured to filter the reflected electrical signal, obtain the filtered reflected electrical signal, and send the filtered reflected electrical signal to the signal processing module 400. It can be understood that the reflected electrical signal output by the detector array 310 includes a common-mode dc component and a noise signal, and therefore, the reflected electrical signal needs to be filtered by the filter array 320 to eliminate the common-mode dc component and the high-frequency signal in the reflected electrical signal, so as to improve the signal-to-noise ratio of the reflected electrical signal.
In one embodiment, the filter is a passive filter. It can be understood that the passive filter, also called as LC filter, is a filter circuit formed by using the combination design of inductor, capacitor and resistor, can filter out a certain or multiple harmonics, and has the advantages of simple structure, low cost, high operation reliability, low operation cost, etc., so the passive filter adopted in the embodiment is beneficial to simplifying the structural design of the laser radar system and reducing the production cost. It is to be understood that the filter may also be an active filter, and the present embodiment is not limited by the type of the filter.
In the TOF chip that is mature at present, the detector array 310, the filter array 320, and the signal processing circuit 400 are integrated, so that the TOF chip can receive the reflected laser signal, convert the reflected laser signal into a reflected electrical signal, obtain a phase offset between the outgoing laser signal and the reflected laser signal according to the reflected electrical signal, and calculate an absolute distance of an object in the detection area according to the phase offset. Therefore, in the actual design process, in order to reduce the design complexity of the lidar system and achieve the miniaturized design of the lidar system, the TOF chip may be used to implement the functions of the detection module 310 and the signal processing module 400, that is, the TOF chip may be used to replace the detection module 310 and the signal processing module 400.
The laser radar system provided by any one of the above embodiments has the basic working principle that: the phase shift amount of the outgoing laser signal and the reflected laser signal of the amplitude modulated continuous wave is proportional to the distance between the object in the detection area and the detection module 300, so that the absolute distance of the object in the detection area can be calculated according to the phase shift amount. Referring to fig. 3, fig. 3 is a schematic view illustrating a measuring principle of measuring a distance by using an outgoing laser signal.
Assuming that the outgoing laser signal of the amplitude modulated continuous wave is a sine wave signal, the absolute distance of the object in the detection area is measured as follows:
let the amplitude of the transmitted sine wave signal s (t) be a, the modulation frequency be f, the received signal after a time delay Δ t be the receiver r (t), the attenuated amplitude be a, and the intensity offset (due to ambient light) be B. N (4 for example) sampling time intervals are equal, and are all T/4, where T is the period of the sinusoidal signal s (T), and the following equation set can be listed according to the sampling time:
s(t)＝a·(1+sin(2πft))
if t0＝0，
Then there is
ri＝r(ti)＝A·(1+sin(2πf(ti-Δt)))+(A+B)
Wherein,
according to the formula, the phase offset can be calculated
Calculating an absolute distance of an object within the detection area from the phase offset
Wherein d is the absolute distance of the object in the detection area, and c is the speed of light.
After calculating the absolute distance of the object in the detection area, the measurement accuracy of the lidar system can be calculated according to the absolute distance, the amplitude after attenuation and the intensity deviation of the reflected laser signal, and the specific calculation process is as follows:
amplitude after attenuation is
The intensity shift is
The measurement accuracy of the laser radar system is
Wherein, the sigmadIndicating the measurement accuracy of the lidar system.
According to the laser radar system, the outgoing laser signals emitted to the detection area are subjected to beam splitting processing through the emission optical system, so that the outgoing laser signals subjected to beam splitting processing uniformly illuminate the whole detection area, the light energy of each detection direction is concentrated after beam splitting, a farther detection distance can be reached, the crosstalk problem among channels in all directions cannot be caused by echoes, interference light signals in the reflected laser signals are reduced, the signal to noise ratio of the reflected electric signals is improved, and the measurement precision and the imaging quality are improved. Secondly, the absolute distance of the object in the detection area is calculated according to the phase offset, and compared with the method of directly measuring the flight time, the method is easier to realize, and the complexity of a back-end circuit is reduced, so that the generation cost is reduced. In addition, the modulation of the outgoing laser signal of the amplitude-modulated continuous wave signal is opposite to pulse modulation, so that the fixed deviation caused by ambient light is eliminated, and the measurement precision is improved.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.