CN103063242A - Real-time monitoring system and method based on optical time domain reflection and fiber grating distributed type - Google Patents

Abstract

The invention relates to a real-time monitoring system and a method based on an optical time domain reflection and fiber grating distributed type. The real-time monitoring system is characterized in that a laser control unit is respectively connected with a laser device and a computer in an electric mode, the laser device is connected with a combined end of a first fiber coupler in an optical mode, two optical splitting ends of the first fiber coupler are respectively connected with a first optical circulator port and a laser device wavelength monitoring unit, a second optical circulator port is connected with a combined end of the second optical fiber coupler in an optical end, one shunting end of the second fiber coupler is connected with a group of fiber gratings in an optical mode, the other shunting ends are respectively connected with the other corresponding groups of fiber gratings in an optical mode through a delayed optical fiber, a third optical circulator port is connected with a photoelectric detector in an optical mode, and the laser device wavelength monitoring unit, the photoelectric detector and the computer are respectively connected with a signal collecting and processing unit in an electric mode. According to the real-time monitoring method, the central wavelength of the fiber gratings can be rapidly demodulated in a real-time mode, and changes of the central wavelength of the plurality of the fiber gratings which are coincided in a working waveband on a sensing periodic line can be distinguished.

Description

Based on optical time domain reflection and the distributed real-time monitoring system of fiber grating and method

Technical field

The present invention relates to technical field of optical fiber sensing, relate in particular to a kind of optical time domain reflection and the distributed real-time monitoring system of fiber grating and method utilized.

Background technology

Distributing optical fiber sensing is to be accompanied by the demand of society and a kind of novel real time on-line monitoring technology developed gradually, ultimate principle is to utilize an optical fiber to transmit simultaneously and perceptual signal, in conjunction with advanced signal processing technology, can survey the physical quantitys such as the temperature that reaches tens kilometers optical fiber diverse locations and strain, realize real distributed measurement.The peculiar light weight of optical fiber, anti-electromagnetic interference (EMI), the advantage such as anticorrosive also make distributed fiberoptic sensor obtain the favor of numerous researchists and application units, have obtained in recent decades huge progress.Up to the present, about Fibre Optical Sensor the research in various fields just carrying out like a raging fire.The Fibre Optical Sensor of the various specific uses such as fibre optic temperature sensor, fibre optic compression sensor, optical fibre displacement sensor and fibre optic current sensor emerges in an endless stream, almost can be applied in the various fields of traditional electricity working sensor, and have sensitivity and the serviceable life higher than traditional electric sensor.

In the various fields of at present relevant Fibre Optical Sensor research, distributed fiberoptic sensor is a class sensor at present the most attractive and development prospect.Distributing optical fiber sensing is the technology of utilizing the optical fiber vertical characteristics to measure, it is measured function as fiber lengths, can on whole fiber lengths, carry out continuous real-time measurement to the external physical parameter along the fiber geometries path profile, space distribution and the time dependent feature thereof of tested physical parameter can be provided for people, can be applied in widely the territory security protection, enclose boundary's intrusion detection, buildings health monitoring, the fields such as oil pipeline monitoring.This class sensor can be divided into following several according to sensing principle: based on the distributed fiberoptic sensor of principle of interference; Distributed fiberoptic sensor based on the optical time domain reflection principle; Distributed fiberoptic sensor based on the bragg grating principle.

Distributed fiberoptic sensor based on the bragg grating principle is to utilize bragg grating centre wavelength temperature and stress and so on physical quantities sensitivity to be carried out the technology of sensing.By at the common a plurality of fiber gratings of optical fiber series connection, can carry out distributed monitoring and the measurement of temperature, strain or other physical quantity.Existing many research institutions and company have carried out a large amount of research and development to it both at home and abroad, at present Major Difficulties is accurately and fast the centre wavelength that demodulates each fiber grating how, the skew of each fiber bragg grating center wavelength of Real-Time Monitoring is with the measured variation in the accurate response external world; Secondly, because each fiber grating needs certain bandwidth that works alone, therefore be subjected to the light source limit bandwidth, the fiber grating quantity that is connected in series on the sensing link can not unconfinedly increase.The method that tradition adopts wideband light source and Fabry-Paro wave filter to survey with Wavelength demodulation all faces above several problem, and can not distinguish the variation of a plurality of fiber bragg grating center wavelengths of service band coincidence on the sensing link.

Summary of the invention

The problem that purpose of the present invention exists in order to overcome above-mentioned prior art, and provide a kind of distributed real-time monitoring system and method based on optical time domain reflection and Fiber Bragg Grating technology, the method can be in real time and is demodulated rapidly the centre wavelength of fiber grating, and can distinguish the variation of a plurality of fiber bragg grating center wavelengths that service band overlaps on the sensing link.

For achieving the above object, the technical solution used in the present invention is:

A kind of based on optical time domain reflection and the distributed real-time monitoring system of fiber grating, comprise laser instrument, laser wavelength monitoring means, two fiber couplers, optical circulator, at least two group fiber-optic grating sensors, postpone optical fiber, photodetector, laser control unit, signals collecting and processing unit, computing machine, it is characterized in that: the laser control unit is electrically connected with laser instrument, computing machine respectively; Laser instrument is connected with the terminal light that closes of the first fiber coupler; Two light splitting ends of the first fiber coupler are connected with optical circulator I port, laser wavelength monitoring means respectively, and wherein the laser wavelength monitoring means is used for the laser emitting Wavelength calibration, guarantee the wavelength measurement precision; Optical circulator II port is connected with the terminal light that closes of the second fiber coupler; A minute terminal of the second fiber coupler is connected with one group of fiber grating light, and residue minute terminal postpones optical fiber and corresponding remaining set fiber grating light connection through one respectively; Optical circulator III port is connected with photodetector light, and signals collecting is electrically connected with laser wavelength monitoring means, photodetector, computing machine respectively with processing unit.

Described laser instrument is Wavelength tunable laser.

The present invention uses has the Wavelength tunable laser of higher scan frequency as probe source, by the laser control unit initial wavelength and the length scanning interval of laser instrument output are set, laser instrument transponder pulse light, each exomonental wavelength is controlled known.

Described two groups of fiber-optic grating sensors are the fiber grating group that two service bands overlap, and all are to be composed in series by the fiber-optic grating sensor that service band does not overlap in every group.

The splitting ratio of fiber coupler is according to the actual conditions choose reasonable; Optical circulator is three ports light rings.

Photodetector is PIN or APD type photodetector, and includes pre-amplification circuit and shaping circuit.

The laser control unit can arrange initial wavelength and the length scanning spacing of Wavelength tunable laser scanning.

The laser wavelength monitoring means includes photodetector, wavelength calibration device, is used for the wavelength that the FEEDBACK CONTROL laser instrument makes it stable output.

Signals collecting and processing unit comprise data acquisition and signal processing two parts, and data acquisition is to be realized by the high-speed figure capture card; In conjunction with the time delay that postpones optical fiber and produce, this capture card can be in time with the reflected signal of two groups of different fiber gratings separately, thereby realize multiplexing on the time domain.

The present invention mainly utilizes optical time domain reflection to solve the identification problem of the fiber-optic grating sensor that a plurality of service bands overlap on the same optical fiber link.The mistiming that is transferred to photodetector by detection fiber optical grating reflection light is identified the fiber grating that a plurality of service bands overlap, and determines its physical location.

Method based on optical time domain reflection and the distributed real-time monitoring system of fiber grating, base is characterised in that by following step and is undertaken: (1) computing machine is set initial scanning wavelength and the length scanning interval of Wavelength tunable laser light source by the laser control unit, scanning fiber bragg grating centre wavelength place wave band;

(2) photodetector is determined the physical location of each fiber-optic grating sensor by fiber-optic grating sensor being carried out position-centre wavelength coding;

(3) when the pulsed light of Wavelength tunable laser emission scans at least two group fiber grating groups, the reflective light intensity of the fiber grating that signals collecting and processing unit overlap by optical time domain reflection differentiation service band;

(4) computing machine is according to the intensity of each fiber Bragg grating reflected signal and the corresponding relation of time, find out the strong reflection time point of each fiber grating in all fiber grating groups, and in conjunction with laser output wavelength-time curve, realize the real-time demodulation of optic fiber grating wavelength, determine temperature and the stress of each fiber-optic grating sensor.

The present invention has following innovative point:

(1) technology that adopts optical time domain reflection to combine with distributed fiber grating can be identified the identical a plurality of fiber gratings of optical parametric on the same optical fiber link, and the system of expanding can monitor fiber grating quantity.

(2) fiber-optic grating sensor is carried out position-centre wavelength coding, utilize Wavelength tunable laser to survey, can separate rapidly each optical fiber grating sensing unit of mediation positioning system by the method for length scanning.

Description of drawings

Fig. 1 is system light path and the circuit diagram of one embodiment of the invention.

Fig. 2 is in two groups of fiber grating situations, when laser instrument scans, and the fiber grating reflectogram.

Embodiment

Below in conjunction with accompanying drawing, embodiment, and in conjunction with the optical time domain reflection principle the invention will be further described:

As shown in Figure 1, based on the distributed real-time monitoring system figure of optical time domain reflection and Fiber Bragg Grating technology, here take two groups of fiber gratings as monitoring target, if need the longer distance of monitoring, can realize by increasing many group fiber gratings.The present invention includes Wavelength tunable laser 1, two fiber couplers (2,4),optical circulator 3, laser wavelength monitoring means 5,photodetector 6,laser control unit 7, signal processing unit 8,computing machine 9, postponeoptical fiber 10, identical two groups of fiber gratings (11,12), wherein every group of fiber grating comprises the optical fiber grating sensing unit that 20 service bands do not overlap;Laser control unit 7 is electrically connected with Wavelength tunable laser 1,computing machine 9 respectively; Wavelength tunable laser 1 is connected with the terminal light that closes of thefirst fiber coupler 2; Two light splitting ends of thefirst fiber coupler 2 are connected with optical circulator 3 I ports 31, laser wavelength monitoring means 5 respectively, and wherein laser wavelength monitoring means 5 is used for Wavelength tunable laser outgoing Wavelength calibration, guarantees the wavelength measurement precision;Optical circulator 3 IIports 32 are connected with the terminal light that closes of the second fiber coupler 4; A minute terminal of the second fiber coupler 4 is connected with one group offiber grating 11 light, another minute terminal postponeoptical fiber 10 through one respectively and organize fiber grating 12 light with another and be connected;Optical circulator 3 III ports 33 are connected withphotodetector 6 light, and signals collecting is electrically connected with laser wavelength monitoring means 7,photodetector 6,computing machine 9 respectively with processing unit 8.

Initial scanning wavelength and the length scanning interval of Wavelength tunable laser 1 are set by laser control unit 7.Here the initial wavelength of hypothesis setting is 1520nm, scans 1560nm and stops.

The every run-down of Wavelength tunable laser is sent a series of burst pulses, and these burst pulse wavelength are incremented to 1560nm from 1520nm.Pulsed light is through 2 light splitting of the first fiber coupler, and wherein a part of light access laserwavelength monitoring means 5 is used as wavelength monitoring, to guarantee the Wavelength demodulation precision; Another part light beam enters optical circulator 3 I ports 31.

Be divided into two parts from the light ofoptical circulator 3 IIports 32 outputs through another fiber coupler 4, a part is directly injected first group offiber grating 11, and another part advanced one section sufficiently long delayoptical fiber 10 and injects second group offiber grating 12.

The light that each fiber grating reflects entersoptical circulator 3 IIports 32 through fiber coupler 4, from 33 outputs ofoptical circulator 3 III ports, entersphotodetector 6, and access signals collecting and processing unit 8, carries out data acquisition and processing.

Owing to postponing the effect ofoptical fiber 10, the light that two groups of fiber gratings reflect arrives the asynchronism(-nization) ofphotodetector 6, therefore according to the optical time domain reflection principle, can on time domain, accurately differentiate the light intensity that two groups of fiber gratings reflect, also can tell the fiber grating that service band overlaps two groups of fiber gratings from time domain thus.

Fiber grating pair different wave length reflectivity is different, determines the centre wavelength of each fiber grating according to laser output wavelength corresponding to strong reflection spot of each fiber grating.

The change of the various physical quantitys such as fiber grating ambient temperature, stress all can cause its centre wavelength to produce skew, therefore according to the accurately variation of demodulating fiber bragg grating external physical quantity of side-play amount of fiber bragg grating center wavelength.

Here in conjunction with Fig. 2 System Working Principle is described further.When having drawn system's operation among the figure, light intensity-time diagram that laser instrument output intensity-time diagram and detector receive.When laser instrument carries out single pass, according to the optical time domain reflection principle, not only can distinguish the fiber grating that service band does not overlap in time, also can clearly distinguish the fiber grating that service band overlaps.In light intensity-time diagram such as the detector reception, centre wavelength is λ in two groups of fiber gratings₁, λ₂, λ₂₀Each two pairs of light that fiber grating reflects, all can distinguish clearly in time.Therefore by the strong reflection spot of each fiber grating of location, in conjunction with laser instrument emission wavelength-time curve, just can demodulate fast the centre wavelength of each fiber grating.

The technology that has adopted optical time domain reflection to combine with distributed fiber grating in view of the present invention, the a plurality of fiber gratings that can the monitoring wave band overlap, broken that the light source bandwidth makes the distributed fiber grating sensing technology can monitor longer distance to the restriction of fiber grating number in the distributed fiber Bragg grating sensor system in the classic method.

The present invention can be widely used in various needs and grows distance, distributed monitoring fields of measurement.

Claims (7)

1. one kind based on optical time domain reflection and the distributed real-time monitoring system of fiber grating, comprise laser instrument, laser wavelength monitoring means, two fiber couplers, optical circulator, at least two group fiber-optic grating sensors, postpone optical fiber, photodetector, laser control unit, signals collecting and processing unit, computing machine, it is characterized in that: the laser control unit is electrically connected with laser instrument, computing machine respectively; Laser instrument is connected with the terminal light that closes of the first fiber coupler; Two light splitting ends of the first fiber coupler are connected with optical circulator I port, laser wavelength monitoring means respectively, and optical circulator II port is connected with the terminal light that closes of the second fiber coupler; A minute terminal of the second fiber coupler is connected with one group of fiber grating light, and residue minute terminal postpones optical fiber and corresponding remaining set fiber grating light connection through one respectively; Optical circulator III port is connected with photodetector light, and signals collecting is electrically connected with laser wavelength monitoring means, photodetector, computing machine respectively with processing unit.

2. according to claim 1 based on optical time domain reflection and the distributed real-time monitoring system of fiber grating, it is characterized in that: described laser instrument is Wavelength tunable laser.

3. according to claim 1 based on optical time domain reflection and the distributed real-time monitoring system of fiber grating, it is characterized in that: described two groups of fiber-optic grating sensors are the fiber grating group that two service bands overlap, and all are to be composed in series by the fiber-optic grating sensor that service band does not overlap in every group.

4. according to claim 1 based on optical time domain reflection and the distributed real-time monitoring system of fiber grating, it is characterized in that: described photodetector is PIN or APD type photodetector, and includes pre-amplification circuit and shaping circuit.

5. according to claim 1 based on optical time domain reflection and the distributed real-time monitoring system of fiber grating, it is characterized in that: described laser control unit can arrange initial wavelength and the length scanning spacing of Wavelength tunable laser scanning.

6. according to claim 1 based on optical time domain reflection and the distributed real-time monitoring system of fiber grating, it is characterized in that: described laser wavelength monitoring means includes photodetector, wavelength calibration device, is used for the wavelength that the FEEDBACK CONTROL laser instrument makes it stable output.

7. described method based on optical time domain reflection and the distributed real-time monitoring system of fiber grating one of according to claim 1-6, base is characterised in that by following step and is undertaken: (1) computing machine is set initial scanning wavelength and the length scanning interval of Wavelength tunable laser light source by the laser control unit, scanning fiber bragg grating centre wavelength place wave band;

(2) photodetector is determined the physical location of each fiber-optic grating sensor by fiber-optic grating sensor being carried out position-centre wavelength coding;

(3) when the pulsed light of Wavelength tunable laser emission scans at least two group fiber grating groups, the reflective light intensity of the fiber grating that signals collecting and processing unit overlap by optical time domain reflection differentiation service band;

(4) computing machine is according to the intensity of each fiber Bragg grating reflected signal and the corresponding relation of time, find out the strong reflection time point of each fiber grating in all fiber grating groups, and in conjunction with laser output wavelength-time curve, realize the real-time demodulation of optic fiber grating wavelength, determine temperature and the stress of each fiber-optic grating sensor.

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