CN113607261A - Optical fiber sensing system with phase-sensitive optical time domain reflection and optical fiber interference fusion - Google Patents
Optical fiber sensing system with phase-sensitive optical time domain reflection and optical fiber interference fusion Download PDFInfo
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- CN113607261A CN113607261A CN202110813912.0A CN202110813912A CN113607261A CN 113607261 A CN113607261 A CN 113607261A CN 202110813912 A CN202110813912 A CN 202110813912A CN 113607261 A CN113607261 A CN 113607261A
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- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
Abstract
The invention relates to an optical fiber sensing system with phase-sensitive optical time domain reflection and optical fiber interference fusion, which comprises a light emitting unit and a first polarization-preserving 3 x 3 optical coupler which are sequentially connected, wherein the first polarization-preserving 3 x 3 optical coupler outputs two-arm optical waves with the phase difference of 2 pi/3, the two-arm optical waves are respectively communicated with one sensing optical cable, the system also comprises a polarization separation structure for separating scattered light and reflected light and a detector for respectively detecting the scattered light and the reflected light in the two sensing optical cables, and the two groups of polarization separation structures are respectively arranged in transmission paths of the two-arm optical waves. Compared with the prior art, the invention integrates the advantages of both the phase-sensitive optical time domain reflection type sensor and the interference type optical fiber sensor to form the distributed sensor with excellent performance.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensing, and particularly relates to an optical fiber sensing system fusing a phase-sensitive optical time domain reflection technology and an optical fiber interference technology.
Background
The research and development work of the optical fiber vibration sensing system is rapidly promoted at home and abroad in recent years, and various products based on different sensing principle routes appear, and the optical fiber vibration sensing system can be divided into a distributed interference type sensing technology and a distributed sensing technology based on an Optical Time Domain Reflectometer (OTDR) according to the technical principle. The distributed interference type optical fiber vibration sensor mainly comprises an M-Z type, a Sagnac type and a Michelson type, and the key point of a sensing structure of the distributed interference type optical fiber vibration sensor is that the distributed interference type optical fiber vibration sensor comprises a sensing arm and a reference arm, when a vibration signal acts on the sensing arm, a phase difference is generated between the two arms, and distributed vibration signal detection is carried out by demodulating the size and the position of the phase difference. The distributed vibration sensing technology based on the OTDR detects the intensity and the position of the vibration signal by detecting the change of the refractive index of the optical fiber and the change of the polarization, the frequency, the phase, the time and the intensity of reflected light caused when the demodulation vibration signal acts on the optical fiber. The types include three types, namely a polarized optical time domain reflection type (POTDR), a Brillouin optical time domain reflection type (BOTDR) and a phase-sensitive optical time domain reflection type (phi-OTDR) sensor. The phi-OTDR vibration sensor detects the phase change of return light of pulses with narrow line width at different positions by using the interference principle of backward Rayleigh scattering light generated in optical fibers, and can demodulate vibration signals at corresponding positions. The vibration sensing technology based on the phi-OTDR can respond to high-frequency and low-frequency signals simultaneously and has high sensitivity.
The interference type optical fiber sensor has wide frequency response capability to vibration, can reflect the characteristics of frequency, size, duration and the like of a vibration signal through the phase change of the medium optical wave of the optical fiber, and has good advantages in the field of vibration mode identification. The phase-sensitive optical time domain reflection type sensor has high sensitivity and can reach the magnitude of meter on the positioning resolution. Therefore, the interference type optical fiber sensor and the phi-OTDR sensor are combined, and the method has a great application prospect in the field of distributed optical fiber intelligent sensing.
Disclosure of Invention
The present invention aims to overcome the defects of the prior art and provide an optical fiber sensing system with the fusion of phase sensitive optical time domain reflection and optical fiber interference.
The purpose of the invention can be realized by the following technical scheme:
the optical fiber sensing system comprises a light emitting unit and a first polarization-maintaining 3 x 3 optical coupler which are sequentially connected, wherein the first polarization-maintaining 3 x 3 optical coupler outputs two-arm optical waves with the phase difference of 2 pi/3, the two-arm optical waves are respectively communicated with one sensing optical cable, the system further comprises a polarization separation structure for separating scattered light and reflected light and a detector for respectively detecting the scattered light and the reflected light in the two sensing optical cables, and 2 groups of the polarization separation structure are respectively arranged in transmission paths of the two-arm optical waves.
Preferably, the polarization separation structure includes a polarization beam splitter/combiner, a faraday rotator and a faraday rotator mirror, a first port of the polarization beam splitter/combiner is connected to a light wave output end of a first polarization 3 × 3 optical coupler, a third port of the polarization beam splitter/combiner is connected to an input end of the faraday rotator, an output end of the faraday rotator is connected to an input end of a sensing optical cable, and an output end of the sensing optical cable is connected to the faraday rotator mirror.
Preferably, there are 4 detectors, two of the detectors are used to detect the scattered light which is emitted from the second port of the polarization beam splitter/combiner and is rotated by 90 °, and the other two detectors are respectively connected to the two ports of the first 3 × 3 optical coupler and are used to detect the reflected light which is emitted from the first port of the polarization beam splitter/combiner and is rotated by 180 °.
Preferably, the polarization separation structure includes a polarization splitting/combining device, a faraday rotator, and a second polarization-maintaining 3 × 3 optical coupler, a first port of the polarization splitting/combining device is connected to an optical wave output end of the first polarization-maintaining 3 × 3 optical coupler, a third port of the polarization splitting/combining device is connected to an input end of the sensing optical cable, an output end of the sensing optical cable is connected to the faraday rotator, and second ports of the polarization splitting/combining devices in the two optical wave transmission paths are respectively connected to the second polarization-maintaining 3 × 3 optical coupler.
Preferably, there are 4 detectors, two of the detectors are used for detecting the non-rotated scattered light exiting from the first port of the polarization beam splitter/combiner, and the other two detectors are respectively connected to the two ports of the second 3 × 3 optical coupler and are used for detecting the reflected light exiting from the second port of the polarization beam splitter/combiner and rotated by 90 °.
Preferably, an attenuator is arranged between the output end of the sensing optical cable and the Faraday rotation mirror.
Preferably, the light emitting unit comprises a light source, an acousto-optic modulator and an optical isolator which are connected in sequence.
Preferably, the light source comprises a narrow spectrum laser or a broad spectrum laser.
Compared with the prior art, the invention has the following advantages:
(1) the invention utilizes the backward scattered light and the reflected light generated by the transmission of the same laser in the optical fiber to construct a system with the fusion of a phase-sensitive optical time domain reflectometer and an optical fiber interferometer, can respectively take the advantages of the systems, realizes a distributed optical fiber sensor with high positioning precision and high mode identification accuracy, adopts the design of an optical fiber light path structure, realizes the separation of the scattered light and the reflected light on a polarization state, and obtains a signal with high signal-to-noise ratio for subsequent signal processing.
(2) The interference type optical fiber sensor has wide frequency response capability to vibration, can reflect the characteristics of frequency, size, duration and the like of a vibration signal through the phase change of an optical wave in an optical fiber, and has good advantages in the field of vibration mode identification; the phase-sensitive optical time domain reflection type has high sensitivity and can reach the magnitude of meter on the positioning resolution; the structure provided by the invention can combine the advantages of the two to form an advanced distributed sensor.
Drawings
Fig. 1 is a schematic structural diagram of an optical fiber sensing system in which phase-sensitive optical time domain reflection and optical fiber interference are fused in embodiment 1 of the present invention;
fig. 2 is a schematic structural diagram of an optical fiber sensing system in which phase-sensitive optical time domain reflection and optical fiber interference are fused in embodiment 2 of the present invention;
FIG. 3 is a schematic diagram of the principle of separating scattered light and reflected light in the polarization direction;
FIG. 4 is a graph showing backscattered light signals obtained from PD1 and PD2 in example 2 of the present invention;
FIG. 5 is a signal processing diagram for obtaining the position of a disturbance signal at a position of 0km in example 2 of the present invention using backscattered light signals obtained in PD1 and PD 2;
FIG. 6 is a signal processing diagram for obtaining the position of a disturbance signal at a position of 4km in example 2 of the present invention using backscattered light signals obtained in PD1 and PD 2;
FIG. 7 is a signal processing diagram of a position of a disturbance signal at a position of 6km obtained using backscattered light signals obtained in PD1 and PD2 in example 2 of the present invention;
FIG. 8 is interference signals of reflected light obtained by using PD3 and PD4 in embodiment 2 of the present invention;
FIG. 9 is a diagram illustrating a light intensity variation signal generated by phase variation obtained by extracting a useful signal from the interference signal of the reflected light obtained in FIG. 5 according to the present invention;
FIG. 10 is a diagram illustrating the phase change information of the optical wave in the optical fiber caused by the disturbance obtained by the reflected signal according to the present invention.
In the figure, LD is a light source, AOM is an acousto-optic modulator, ISO is an optical isolator, OC1 and OC2 are polarization maintaining 3 × 3 optical couplers, PBS1 and PBS2 are polarization splitting/combining beam splitters, FR1 and FR2 are faraday rotators, FRM1 and FRM2 are faraday rotators, VOA1 and VOA2 are attenuators, and PD1, PD2, PD3 and PD4 are detectors.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments. Note that the following description of the embodiments is merely a substantial example, and the present invention is not intended to be limited to the application or the use thereof, and is not limited to the following embodiments.
Example 1
As shown in fig. 1, the present embodiment provides an optical fiber sensing system with phase-sensitive optical time domain reflection and optical fiber interference fusion, which includes a light emitting unit and a first polarization maintaining 3 × 3 optical coupler connected in sequence, where the first polarization maintaining 3 × 3 optical coupler outputs two optical waves with a phase difference of 2 pi/3, the two optical waves are respectively communicated with one optical sensing cable (common optical cable), the system further includes a polarization separation structure for separating scattered light from reflected light and a detector for respectively detecting the scattered light and the reflected light in the two optical sensing cables, and the polarization separation structure is provided with 2 groups, which are respectively disposed in transmission paths of the two optical waves. The light emitting unit comprises a light source, an acousto-optic modulator and an optical isolator which are sequentially connected, and the light source comprises a narrow-linewidth laser or a wide-spectrum laser.
The polarization separation structure comprises a polarization beam splitter/combiner, a Faraday rotator and a Faraday rotator mirror, wherein a first port of the polarization beam splitter/combiner is connected with a light wave output end of a first polarization-preserving 3 x 3 optical coupler, a third port of the polarization beam splitter/combiner is connected with an input end of the Faraday rotator, an output end of the Faraday rotator is connected with an input end of a sensing optical cable, an output end of the sensing optical cable is connected with the Faraday rotator mirror, and an attenuator is arranged between the output end of the sensing optical cable and the Faraday rotator mirror. The detectors are 4, two of the detectors are used for detecting the scattered light which is emitted from the second port of the polarization beam splitter/combiner and is rotated by 90 degrees, and the other two detectors are respectively connected with the two ports of the first 3 x 3 optical coupler and are used for detecting the reflected light which is emitted from the first port of the polarization beam splitter/combiner and is rotated by 180 degrees. The embodiment realizes the optical path of the fusion of the phase-sensitive optical time domain reflection technology and the Michelson optical fiber interference technology
In this embodiment, OC is a first polarization maintaining 3 × 3 optical coupler, and when coherent light waves generated by a laser are transmitted in an optical fiber, generated backward scattering light generates an interference phenomenon due to coherence thereof, which can reflect phase change caused by vibration on a sensing optical cable; the acousto-optic modulator modulates continuous light emitted by the laser into pulse light with high extinction ratio and adjustable duty ratio; the phase difference of the two light waves of the first polarization-preserving 3 x 3 optical coupler is a fixed value of 2 pi/3, and the tail fibers are sensing optical cables; the polarization beam splitter/combiner strictly performs light throughput according to the polarization state of the light wave; the Faraday rotator rotates the polarization direction of the single polarized light wave passing in one direction by 45 degrees, and the rotation angle of 90 degrees is generated by two passes; the optical attenuator controls the optical power of the light wave reaching the tail end reflecting mirror; the Faraday rotator mirror rotates the light wave reaching the tail end by 45 degrees before being reflected, rotates the light wave by 45 degrees again after being reflected, and finally changes the transmission direction of the light wave by 180 degrees and the polarization direction by 90 degrees after passing through the Faraday rotator. If the signal light enters from the port 1 of the polarization beam splitter/combiner, the signal light exits from the port 3 of the polarization beam splitter/combiner, then enters the sensing optical fiber after passing through the faraday rotator, the scattered light and the reflected light reach the polarization beam splitter/combiner after passing through the faraday rotator again, the reflected light rotated by 180 degrees exits from the port 1 of the polarization beam splitter/combiner, and the scattered light rotated by 90 degrees exits from the port 2 of the polarization beam splitter/combiner.
Example 2
As shown in fig. 1, the present embodiment provides an optical fiber sensing system with phase-sensitive optical time domain reflection and optical fiber interference fusion, including a light emitting unit and a first polarization maintaining 3 × 3 optical coupler connected in sequence, where the first polarization maintaining 3 × 3 optical coupler outputs two optical waves with a phase difference of 2 pi/3, the two optical waves are respectively communicated with one optical sensing cable, the system further includes a polarization separation structure for separating scattered light from reflected light and a detector for respectively detecting the scattered light and the reflected light in the two optical sensing cables, and the polarization separation structure is provided with 2 groups, which are respectively disposed in transmission paths of the two optical waves. The light emission unit comprises a light source, an acousto-optic modulator and an optical isolator which are sequentially connected, and the light source comprises a narrow linewidth laser.
The polarization separation structure comprises a polarization beam splitter/combiner, a Faraday rotation mirror and a second polarization-maintaining 3X 3 optical coupler, wherein a first port of the polarization beam splitter/combiner is connected with an optical wave output end of the first polarization-maintaining 3X 3 optical coupler, a third port of the polarization beam splitter/combiner is connected with an input end of a sensing optical cable, an output end of the sensing optical cable is connected with the Faraday rotation mirror, second ports of the polarization beam splitter/combiner in two optical wave transmission paths are respectively connected to the second polarization-maintaining 3X 3 optical coupler, and an attenuator is arranged between the output end of the sensing optical cable and the Faraday rotation mirror. The detectors are 4, two of the detectors are used for detecting the scattered light without rotation emitted from the first port of the polarization beam splitter/combiner, and the other two detectors are respectively connected with the two ports of the second 3 x 3 optical coupler and are used for detecting the reflected light which is emitted from the second port of the polarization beam splitter/combiner and is rotated by 90 degrees. The embodiment realizes a phase-sensitive optical time domain reflection technology and polarization-stable MZ fiber interference technology fused optical path structure.
In this embodiment, OC1 is a first polarization maintaining 3 × 3 optical coupler and OC2 is a second polarization maintaining 3 × 3 optical coupler. Specifically, unlike embodiment 1, since there is no faraday rotator, the scattered light in the sensing cable enters directly back into PBS1 and PBS2 without rotation and is detected by PD1 and PD2, and the reflected light rotated by 90 ° by the faraday rotator is output from the second ports of PBS1 and PBS2 and passes through the second polarization maintaining 3 × 3 optical coupler and is detected by PD3 and PD 4.
In both embodiments of the present invention, the scattered light and the reflected light are separated in the polarization direction, the principle is shown in fig. 3, the backward scattered light in the optical fiber will reach the port 3 of the PBS before the reflected light, and the polarization states of the scattered light and the reflected light are perpendicular to each other, and when the scattered light exits from the port 1, the reflected light exits from the port 2. When the faraday rotator is incorporated in the optical fiber, the scattered light exits from the port 2, and the reflected light exits from the port 1.
The scattered light signals obtained by performing the experiment using the system of example 2 as an example are shown in fig. 4, and the results obtained after processing the scattered light signals collected when the optical fiber is disturbed at 0km, 4km and 6km are shown in fig. 5, 6 and 7, respectively. During disturbance, the pulse interference signals acquired at the same time are shown in fig. 8, the pulse signals are extracted to obtain disturbance interference signals shown in fig. 9, and finally, the phase demodulation algorithm is adopted to obtain light wave phase change signals generated by disturbance shown in fig. 10.
The above embodiments are merely examples and do not limit the scope of the present invention. These embodiments may be implemented in other various manners, and various omissions, substitutions, and changes may be made without departing from the technical spirit of the present invention.
Claims (8)
1. The optical fiber sensing system is characterized by comprising a light emitting unit and a first polarization-maintaining 3 x 3 optical coupler which are sequentially connected, wherein the first polarization-maintaining 3 x 3 optical coupler outputs two arms of light waves with the phase difference of 2 pi/3, the two arms of light waves are respectively communicated with one path of sensing optical cable, the system also comprises a polarization separation structure for separating scattered light and reflected light and a detector for respectively detecting the scattered light and the reflected light in the two paths of sensing optical cables, and 2 groups of the polarization separation structure are respectively arranged in transmission paths of the two arms of light waves.
2. The phase-sensitive optical time domain reflectometry and fiber optic interference fusion fiber sensing system of claim 1, wherein the polarization separation structure comprises a polarization beam splitter/combiner, a faraday rotator and a faraday rotator mirror, a first port of the polarization beam splitter/combiner is connected to the optical wave output end of the first polarization maintaining 3 x 3 optical coupler, a third port of the polarization beam splitter/combiner is connected to the input end of the faraday rotator, the output end of the faraday rotator is connected to the input end of the sensing optical cable, and the output end of the sensing optical cable is connected to the faraday rotator mirror.
3. The system of claim 2, wherein there are 4 detectors, two of the detectors are used to detect the scattered light that is emitted from the second port of the polarization beam splitter/combiner and is rotated by 90 °, and the other two detectors are respectively connected to the two ports of the first 3 x 3 optical coupler and are used to detect the reflected light that is emitted from the first port of the polarization beam splitter/combiner and is rotated by 180 °.
4. The phase-sensitive optical time domain reflectometry and optical fiber interference fusion optical fiber sensing system of claim 1, wherein the polarization separation structure comprises a polarization beam splitter/combiner, a faraday rotator mirror and a second polarization-maintaining 3 x 3 optical coupler, a first port of the polarization beam splitter/combiner is connected to an optical wave output end of the first polarization-maintaining 3 x 3 optical coupler, a third port of the polarization beam splitter/combiner is connected to an input end of the sensing optical cable, an output end of the sensing optical cable is connected to the faraday rotator mirror, and second ports of the polarization beam splitter/combiner in the two optical wave transmission paths are respectively connected to the second polarization-maintaining 3 x 3 optical coupler.
5. The system of claim 4, wherein there are 4 detectors, two of the detectors are used to detect the non-rotated scattered light exiting from the first port of the polarization beam splitter/combiner, and the other two detectors are respectively connected to the two ports of the second 3 x 3 optical coupler and are used to detect the reflected light exiting from the second port of the polarization beam splitter/combiner, which is rotated by 90 °.
6. The optical fiber sensing system for the fusion of the phase-sensitive optical time domain reflectometry and the optical fiber interference as claimed in claim 2 or 4, wherein an attenuator is arranged between the output end of the sensing optical cable and the Faraday rotator mirror.
7. The system of claim 1, wherein the optical transmitter comprises a light source, an acousto-optic modulator and an optical isolator connected in sequence.
8. The phase-sensitive optical time domain reflectometry fused fiber optic sensing system of claim 7 wherein the light source comprises a narrow spectrum laser or a broad spectrum laser.
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Citations (4)
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|---|---|---|---|---|
| CN102809421A (en) * | 2011-06-01 | 2012-12-05 | 电子科技大学 | Multi-point localizable distribution-type optical-fiber vibration sensor based on polarization-state differential detection |
| CN110160627A (en) * | 2019-05-31 | 2019-08-23 | 太原理工大学 | The optical fiber sound sensor system of Michelson interference and phase sensitive optical time domain reflection |
| CN110940364A (en) * | 2019-11-26 | 2020-03-31 | 复旦大学 | Distributed two-arm sensing system based on Michelson interferometer |
| AU2020103313A4 (en) * | 2020-11-09 | 2021-01-14 | Harbin Engineering University | A distributed optical fiber Fizeau interferometer based on the principle of optical time domain reflection (OTDR) |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102809421A (en) * | 2011-06-01 | 2012-12-05 | 电子科技大学 | Multi-point localizable distribution-type optical-fiber vibration sensor based on polarization-state differential detection |
| CN110160627A (en) * | 2019-05-31 | 2019-08-23 | 太原理工大学 | The optical fiber sound sensor system of Michelson interference and phase sensitive optical time domain reflection |
| CN110940364A (en) * | 2019-11-26 | 2020-03-31 | 复旦大学 | Distributed two-arm sensing system based on Michelson interferometer |
| AU2020103313A4 (en) * | 2020-11-09 | 2021-01-14 | Harbin Engineering University | A distributed optical fiber Fizeau interferometer based on the principle of optical time domain reflection (OTDR) |
Non-Patent Citations (1)
| Title |
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| ZHU TAO: "Modulated pulses based distributed vibration sensing with high frequency response and spatial resolution", 《OPTICS EXPRESS》 * |
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