Brillouin frequency shift extraction device and method based on bidirectional integration

Abstract

The present invention relates to the field of distributed optical fiber sensing technology, and specifically to a Brillouin frequency shift extraction device and method based on bidirectional integration, in which the laser emitted by a narrow line width laser is divided into two beams by a first coupler, one beam is converted into pulse light by a pulse modulator and enters a sensing optical fiber after passing through an optical circulator, and the backward Brillouin scattering signal generated in the sensing optical fiber enters a second coupler after being emitted by the optical circulator; the other beam enters the second coupler after passing through a polarization scrambler; the beat frequency signal output from the second coupler is received by a photodetector, the generated electrical signal is mixed with the radio frequency signal generated by a signal generator in a mixer, and then sent to a data acquisition and processing system to obtain the Brillouin gain spectrum at each position, and then the Brillouin gain spectrum at each position is respectively processed by forward integration and / or backward integration, and the Brillouin frequency shift spectrum along the sensing optical fiber is obtained as a result. The present invention effectively improves the measurement accuracy of Brillouin frequency shift under low signal-to-noise ratio conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of distributed optical fiber sensing, and in particular to a Brillouin frequency shift extraction device and method based on bidirectional integration, which are used to improve the measurement accuracy of Brillouin frequency shift (BFS). Background Art

[0002] As an important part of fiber optic sensing technology, Brillouin fiber optic sensing technology uses optical fiber as a transmission element and a detection element to achieve distributed measurement. It has been widely used in road safety monitoring, smart grid construction, oil and gas pipeline monitoring and other fields to protect people's lives and safety.

[0003] Brillouin fiber sensing technology measures the changes in temperature and strain acting on the optical fiber by collecting the Brillouin gain spectrum of the optical fiber and extracting the Brillouin frequency shift. The peak frequency of the Brillouin gain spectrum corresponds to the Brillouin frequency shift, and the value of the Brillouin frequency shift is related to the refractive index and acoustic wave velocity of the optical fiber. When the external temperature changes or strain occurs, the refractive index and acoustic wave velocity of the optical fiber will change accordingly, thereby causing a change in the amount of Brillouin frequency shift. Using the linear relationship between the Brillouin frequency shift of the optical fiber and temperature and strain, sensing technology can achieve distributed measurement. Therefore, it is very important to accurately extract the Brillouin frequency shift through the Brillouin gain spectrum.

[0004] The traditional method of extracting Brillouin frequency shift is mainly curve fitting, including Lorentz fitting, Gaussian fitting and Pseudo-Voigt fitting. This scheme is essentially an algorithm that solves the optimal solution of the curve through iterative operations. The curve fitting method depends on the selection of initialization parameters. If the parameter selection deviation is large, the number of iterations will increase exponentially, and even overfitting will occur, resulting in incorrect extraction of Brillouin frequency. In addition, the cross-correlation method has been proposed to avoid the problem of initialization of curve fitting parameters, but it has the problem of mutual constraints between extraction accuracy and measurement time. With the continuous development of neural networks and deep learning, emerging technical means have also been used to extract Brillouin frequency shift, including convolutional neural networks, support vector machines, pattern recognition, etc. Such technologies require a large amount of data training to explore the best parameters, so the extraction accuracy is mainly determined by the number of training sets and the setting of model parameters. Therefore, how to accurately and real-time extract Brillouin frequency shift is an urgent problem to be solved in Brillouin fiber optic sensing technology. Summary of the invention

[0005] The present invention overcomes the characteristics of inaccurate and poor real-time performance of Brillouin frequency shift extraction in the prior art, and provides a Brillouin frequency shift extraction device and method based on bidirectional integration to accurately and real-time extract the Brillouin frequency shift and realize distributed optical fiber sensing.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a Brillouin frequency shift extraction device based on bidirectional integration, comprising: a narrow linewidth laser, a first coupler, a pulse modulator, an optical circulator, a sensing fiber, a polarization scrambler, a second coupler, a photodetector, a mixer, a signal generator, and a data acquisition and processing system;

[0007] The laser light emitted by the narrow linewidth laser is divided into two beams by the first coupler, one beam is used as the detection light and becomes the pulse light after passing through the pulse modulator, the pulse light enters the sensing optical fiber after passing through the optical circulator, the back Brillouin scattering signal generated in the sensing optical fiber is emitted by the optical circulator and enters one input end of the second coupler; the other beam is used as the reference light and enters the other input end of the second coupler after passing through the polarization scrambler;

[0008] The beat frequency signal output from the output end of the second coupler is received by the photoelectric detector for photoelectric conversion, the generated electrical signal is mixed with the radio frequency signal generated by the signal generator in the mixer, and the low-frequency signal obtained by mixing is sent to the data acquisition and processing system;

[0009] The data acquisition and processing system is used to acquire the low-frequency signal obtained by mixing to obtain the Brillouin gain spectrum at each position, and then perform forward integration and / or backward integration processing on the Brillouin gain spectrum at each position, and obtain the Brillouin frequency shift spectrum along the sensing optical fiber according to the integration result.

[0010] The Brillouin frequency shift extraction device based on bidirectional integration also includes an amplifier, a bandpass filter, and a detector. The low-frequency signal obtained by mixing is amplified, filtered, and detected by the amplifier, the bandpass filter, and the detector in turn, and then sent to the data acquisition and processing system.

[0011] The Brillouin frequency shift extraction device based on bidirectional integration further includes a first optical attenuator and a second optical attenuator;

[0012] The first attenuator is arranged before the pulse modulator, and is used for attenuating the intensity of the laser entering the pulse modulator;

[0013] The second attenuator is arranged in the reference light path, and is used for attenuating the intensity of the reference light.

[0014] The Brillouin frequency shift extraction device based on bidirectional integration also includes a pulse amplifier and an erbium-doped fiber amplifier; the pulse amplifier is arranged after the pulse modulator and is used to amplify the pulse light output by the pulse modulator;

[0015] The erbium-doped fiber amplifier is arranged between the optical circulator and the second coupler, and is used for amplifying the backward Brillouin scattering signal generated in the sensing optical fiber.

[0016] The Brillouin frequency shift extraction device based on bidirectional integration further includes: a first optical filter and a second optical filter;

[0017] The first optical filter is arranged at the output end of the pulse amplifier and is used to filter the pulse light;

[0018] The second optical filter is arranged at the output end of the erbium-doped fiber amplifier and is used for filtering the backward Brillouin scattering signal generated in the sensing optical fiber.

[0019] The data acquisition and processing system performs forward integration and / or backward integration processing on the Brillouin gain spectrum at each position to obtain a forward integrated spectrum and / or a backward integrated spectrum, and then uses the frequency corresponding to the maximum slope in the forward integrated spectrum or the backward integrated spectrum as the Brillouin frequency shift value.

[0020] The narrow linewidth laser has a central wavelength of 1550nm and a linewidth of 3kHz.

[0021] In addition, the present invention also provides a Brillouin frequency shift extraction method based on bidirectional integration, which is implemented based on the above-mentioned device and is characterized in that it includes the following steps:

[0022] S1, collecting Brillouin signals at various positions in the sensing optical fiber to obtain a Brillouin gain spectrum;

[0023] S2, performing forward or backward integration on the Brillouin gain spectrum at each position to obtain a forward integrated spectrum or a backward integrated spectrum;

[0024] S3. Find the frequency corresponding to the position with the maximum slope in the forward integrated spectrum or the backward integrated spectrum as the Brillouin frequency shift value at that position, and then obtain the Brillouin frequency shift value at each position in the sensing optical fiber.

[0025] The integral formula is:

[0026]

[0027]

[0028] Where G1(v) represents the amplitude corresponding to frequency v in the forward integrated spectrum, G2(v) represents the amplitude corresponding to frequency v in the backward integrated spectrum, g(x) represents the amplitude at frequency x in the Brillouin gain spectrum, and v1 and v2 are the initial and end frequencies of the Brillouin gain spectrum.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The present invention extracts the Brillouin frequency shift by integrating the gain spectrum without performing parameter initialization operations, thereby effectively avoiding problems such as overfitting caused by parameter initialization selection and effectively improving the measurement accuracy of the Brillouin frequency shift under low signal-to-noise ratio conditions.

[0031] (2) The present invention processes the raw data transmitted by the direct data acquisition system, and does not require the training of the Brillouin frequency shift extraction model, which greatly saves the measurement time and can be applied to the extraction of Brillouin frequency shift under different parameters and different scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram of the structure of a Brillouin frequency shift extraction device based on bidirectional integration provided in Embodiment 1 of the present invention;

[0033] Figure 2 A schematic diagram of the structure of a Brillouin frequency shift extraction device based on bidirectional integration provided in Embodiment 2 of the present invention;

[0034] Figure 3 A comparison diagram of the Brillouin gain spectrum obtained by the present invention and the original Brillouin gain spectrum;

[0035] Figure 4 This is the Brillouin frequency shift result diagram extracted by the present invention.

[0036] Figure 5 This is a comparison diagram of the uncertainty of the extraction results of the present invention and the Lorentz fitting at different frequency intervals.

[0037] In the figure: 1 is a narrow linewidth laser, 2 is a first coupler, 3 is a first optical attenuator, 4 is a pulse modulator, 5 is a pulse amplifier, 6 is a first optical filter, 7 is an optical circulator, 8 is a sensing optical fiber, 9 is a second optical attenuator, 10 is a polarization scrambler, 11 is an erbium-doped fiber amplifier, 12 is a second optical filter, 13 is a second coupler, 14 is a photodetector, 15 is a mixer, 16 is a signal generator, 17 is an amplifier, 18 is a bandpass filter, 19 is a detector, and 20 is a data acquisition and processing system. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0039] Embodiment 1

[0040] like Figure 1 As shown, the first embodiment of the present invention provides a Brillouin frequency shift extraction device based on bidirectional integration, including: a narrow linewidth laser 1, a first coupler 2, a pulse modulator 4, an optical circulator 7, a sensing optical fiber 8, a polarization scrambler 10, a second coupler 13, a photodetector 14, a mixer 15, a signal generator 16, and a data acquisition and processing system 20;

[0041] The laser light emitted by the narrow linewidth laser 1 is divided into two beams by the first coupler 2, one beam is used as the detection light and becomes the pulse light after passing through the pulse modulator 4, the pulse light enters the sensing optical fiber 8 after passing through the optical circulator 7, and the back Brillouin scattered signal generated in the sensing optical fiber 8 enters one input end of the second coupler 13 after being emitted by the optical circulator; the other beam is used as the reference light and enters the other input end of the second coupler 13 after passing through the polarization scrambler 10;

[0042] The beat frequency signal output from the output end of the second coupler 13 is received by the photodetector 14 for photoelectric conversion, and the generated electrical signal is mixed with the radio frequency signal generated by the signal generator 16 in the mixer 15, and the low frequency signal obtained by mixing is sent to the data acquisition and processing system 20;

[0043] The data acquisition and processing system 20 is used to acquire the low-frequency signal obtained by mixing to obtain the Brillouin gain spectrum, and then perform forward integration or backward integration processing on the Brillouin gain spectrum at each position, and obtain the Brillouin frequency shift spectrum along the sensing optical fiber 8 according to the integration result.

[0044] Furthermore, in this embodiment, the data acquisition and processing system 20 is used to use the frequency corresponding to the maximum slope in the forward integrated spectrum or the backward integrated spectrum as the Brillouin frequency shift value.

[0045] Specifically, in this embodiment, the first coupler 2 and the second coupler 13 are optical fiber couplers. In addition, each device is connected through a single-mode optical fiber jumper.

[0046] Specifically, in this embodiment, the central wavelength of the narrow linewidth laser 1 is 1550nm, and the linewidth is 3kHz. The extinction ratio of the pulse modulator 4 is >50db. The sensing fiber 8 adopts SMF, the polarization scrambler 10 adopts PCD-003, and the photodetector 14 adopts KG-PT-12G-A-SM-FA.

[0047] The working principle of this embodiment is described below.

[0048] a. The narrow linewidth laser 1 generates a continuous laser with an operating wavelength of 1550nm, which is divided into two optical paths after passing through the first optical fiber coupler in sequence. One optical path is used as a pulse signal and enters the sensing optical fiber 8 through the optical circulator 7. The detection signal undergoes a spontaneous Brillouin effect in the sensing optical fiber 8 to generate a Brillouin scattering signal. The generated backward Brillouin scattering signal is emitted through the optical circulator 7;

[0049] b. The other output of the first fiber coupler is used as a reference optical signal and is scrambled by a polarization scrambler;

[0050] c. The Brillouin scattering signal in the sensing optical fiber 8 is coupled and beat with the reference signal output by the polarization scrambler after being output by the optical circulator 7. The generated beat signal enters the photodetector for photoelectric conversion. The generated electrical signal is mixed with the radio frequency signal generated by the signal generator in the mixer to achieve the down-conversion of the Brillouin scattering signal. The difference frequency (low frequency) signal obtained by mixing is sent to the data acquisition and processing system to collect the output signal of the detector to obtain the Brillouin gain spectrum, and then the Brillouin gain spectrum signal collected from each sampling position is forward integrated and / or backward integrated to obtain the Brillouin frequency shift BFS information along the optical fiber.

[0051] Among them, the Brillouin scattering signal output by the photodetector is mixed with the electrical signal output by the signal generator in a mixer, so that the Brillouin scattering can be moved to a low-frequency signal near 200MHz.

[0052] Specifically, the intrinsic Brillouin gain spectrum has a Lorentzian type, which is expressed as:

[0053]

[0054] Where g0 is the Brillouin gain coefficient, w is the half-width of the Brillouin gain spectrum, and v b is the Brillouin frequency shift, v1 and v2 are the initial frequency and end frequency of the Brillouin gain spectrum, and g(x) represents the amplitude of the Brillouin gain spectrum at frequency x.

[0055] Then the expressions of the forward integrated spectrum and the backward integrated spectrum are:

[0056]

[0057]

[0058] G1(v) is the amplitude of the forward integrated spectrum at frequency v, the integral expression, and G2 is the amplitude of the backward integrated spectrum at frequency v. The forward integrated spectrum and the backward integrated spectrum obtained both have the maximum slope at the Brillouin frequency shift (BFS), so the Brillouin frequency shift value can be obtained by the corresponding frequency at the maximum slope of the forward integrated spectrum and the backward integrated spectrum.

[0059] Embodiment 2

[0060] like Figure 2 As shown, the second embodiment of the present invention provides a Brillouin frequency shift extraction device based on bidirectional integration, which is the same as the first embodiment, and includes: a narrow linewidth laser 1, a first coupler 2, a pulse modulator 4, an optical circulator 7, a sensing fiber 8, a polarization scrambler 10, a second coupler 13, a photodetector 14, a mixer 15, a signal generator 16, and a data acquisition and processing system 20. Different from the first embodiment, in this embodiment, the Brillouin frequency shift extraction device based on bidirectional integration described in this embodiment further includes an amplifier 17, a bandpass filter 18, and a detector 19. The low-frequency signal obtained by mixing is amplified, filtered, and detected by the amplifier 17, the bandpass filter 18, and the detector 19 in turn, and then sent to the data acquisition and processing system 20.

[0061] Furthermore, this embodiment also includes a first optical attenuator 3 and a second optical attenuator 9; the first attenuator 3 is arranged before the pulse modulator 4 to attenuate the intensity of the laser entering the pulse modulator 4; the second attenuator 3 is arranged in the reference light path to attenuate the intensity of the reference light.

[0062] Furthermore, the present embodiment also includes a pulse amplifier 5 and an erbium-doped fiber amplifier 11; the pulse amplifier 5 is arranged after the pulse modulator 4, and is used to amplify the pulse light output by the pulse modulator 4; the erbium-doped fiber amplifier 11 is arranged between the optical circulator 7 and the second coupler 13, and is used to amplify the backward Brillouin scattering signal generated in the sensing optical fiber 8.

[0063] Furthermore, this embodiment also includes: a first optical filter 6 and a second optical filter 12; the first optical filter 6 is arranged at the output end of the pulse amplifier 5, and is used to filter the pulse light; the second optical filter 12 is arranged at the output end of the erbium-doped fiber amplifier 11, and is used to filter the backward Brillouin scattering signal generated in the sensing optical fiber 8.

[0064] Specifically, in this embodiment, the first coupler 2 and the second coupler 13 are optical fiber couplers, and in addition, each device is connected through a single-mode optical fiber jumper. That is: the output end of the narrow linewidth laser 1 is connected to the input end of the first coupler 2 having two output ends through a single-mode optical fiber jumper; one output end of the first coupler 2 is connected to the input end of the first optical attenuator 3 through a single-mode optical fiber jumper; the output end of the first optical attenuator 3 is connected to the input end of the pulse modulator 4 through a single-mode optical fiber jumper; the output end of the pulse modulator 4 is connected to the input end of the pulse amplifier 5 through a single-mode optical fiber jumper; the output end of the pulse amplifier 5 is connected to the input end of the pulse modulator 4 through a single-mode optical fiber jumper; The optical fiber coupler 2 is connected to the incident end of the first optical filter 6; the output end of the first optical filter 6 is connected to the incident end of the optical circulator 7 through a single-mode optical fiber jumper; the reflection end of the optical circulator 7 is connected to the input sensing optical fiber 8 through a single-mode optical fiber jumper; the output end of the optical circulator 7 is connected to the incident end of the erbium-doped fiber amplifier 11 through a single-mode optical fiber jumper; the output end of the erbium-doped fiber amplifier 11 is connected to the incident end of the second optical filter 12 through a single-mode optical fiber jumper; the other output end of the first optical fiber coupler 2 The output end of the second optical attenuator 9 is connected to the input end of the polarization scrambler 10 through a single-mode optical fiber jumper; the output end of the polarization scrambler 10 and the output end of the second optical filter 12 are respectively connected to the input end of the second optical fiber coupler 13 through a single-mode optical fiber jumper; the output end of the second optical fiber coupler 13 is connected to the input end of the photodetector 14 through a single-mode optical fiber jumper; the output end of the photodetector 14 is connected to the mixer through a radio frequency line. 15 is connected; the output end of the signal generator 16 is connected to the other input end of the mixer 15 through the radio frequency line; the output end of the mixer 15 is connected to the input end of the low noise amplifier 17 through the radio frequency line; the output end of the low noise amplifier 17 is connected to the input end of the band pass filter 18 through the radio frequency line; the output end of the band pass filter 18 is connected to the input end of the detector 19 through the radio frequency line; the output end of the detector 19 is connected to the data acquisition and processing system 20 through the radio frequency line.

[0065] In the specific implementation, the central wavelength of the narrow linewidth laser 1 is 1550nm, the linewidth is 3KHz, the extinction ratio of the pulse modulator 4 is>50db, the pulse amplifier 5 is LSM-EDFA-C-PL-ns-10-S, the sensing fiber 8 adopts SMF, the polarization scrambler 10 adopts PCD-003, the erbium-doped fiber amplifier 11 adopts EDFA-C-PA-45-M, and the photodetector 14 adopts KG-PT-12G-A-SM-FA.

[0066] The working principle of this embodiment is described below.

[0067] a. The narrow linewidth laser generates a continuous laser with an operating wavelength of 1550nm, which is divided into two optical paths after passing through the first optical fiber coupler in sequence. One optical path is a pulse signal and passes through the pulse amplifier, the first optical filter, and the optical circulator in sequence to be amplified, filtered, and circulated into the sensing optical fiber. The detection signal undergoes a spontaneous Brillouin effect in the optical fiber to generate a Brillouin scattering signal. The generated backward Brillouin scattering signal is emitted through the optical circulator and then enters the erbium-doped fiber amplifier and the second optical filter in sequence for amplification and filtering;

[0068] b. The other output of the first fiber coupler is used as a reference optical signal, which is attenuated and scrambled by the second optical attenuator and the polarization scrambler in turn;

[0069] c. The amplified and filtered backscattered signal and the reference signal output by the polarization scrambler enter the second optical fiber coupler for coupling and beat frequency. The generated beat frequency signal enters the photodetector for photoelectric conversion. The generated electrical signal is mixed with the radio frequency signal generated by the signal generator in the mixer to achieve frequency reduction of the Brillouin scattering signal. The down-converted signal is amplified, filtered and detected by the low-noise amplifier 17, the bandpass filter 18 and the detector 19 in turn. The data acquisition and processing system collects and integrates the output signal of the detector to obtain the Brillouin frequency shift BFS information along the optical fiber.

[0070] like Figure 3 As shown, (a) is a schematic diagram of the original Brillouin gain spectrum obtained, wherein the horizontal axis represents frequency, the vertical axis represents sensing distance, and the lighter the color, the larger the amplitude; (b) is a schematic diagram of the integrated Brillouin gain spectrum G(v) obtained by the forward integral spectrum and the backward integral spectrum, wherein, with the Brillouin frequency shift value BFS as the boundary, when the frequency v is less than BFS, G(v)=G1(v), and when v≥BFS, G(v)=G2(v).

[0071] In the specific implementation, for each sampling position in the sensing optical fiber, the Brillouin gain spectrum signal is collected; the Brillouin gain spectrum signals at different positions of the optical fiber are integrated respectively, and the center frequency obtained by the integration is used as the Brillouin frequency shift to obtain the actual Brillouin frequency shift corresponding to different positions in the optical fiber. The measurement results are as follows: Figure 4 The BFS value corresponding to the original signal is obtained by directly extracting the peak value of the Brillouin frequency shift value. It can be seen that the signal-to-noise ratio of the BFS value obtained by the integral extraction of the present invention is greatly reduced.

[0072] In order to compare the performance of the present invention and the Lorentz fitting extraction method, after obtaining the actual Brillouin frequency shift corresponding to different positions in the optical fiber, the scanning interval for obtaining the original Brillouin gain spectrum is changed, and the uncertainty of the Brillouin frequency shift extraction results of the present invention and the traditional Lorentz fitting is calculated respectively. Among them, the uncertainty is calculated based on the mean square error at different sensing distances. Among them, the specific method of changing the scanning interval for obtaining the original Brillouin gain spectrum is: changing the signal frequency output by the signal generator 16 so that it scans between 10.52GHz-10.72GHz, thereby realizing the scanning of the Brillouin gain spectrum. When the frequency scanning interval is 2MHz, 4MHz, 6MHz, 8MHz, and 10MHz, the uncertainty of the Brillouin frequency shift extracted by the present invention and Lorentz is calculated respectively, and the results are as shown in the figure. Figure 5 shown.

[0073] Embodiment 3

[0074] Embodiment 3 of the present invention provides a Brillouin frequency shift extraction method based on bidirectional integration, which is implemented based on a device described in Embodiment 1 or Embodiment 2 and includes the following steps:

[0075] S1, collecting Brillouin signals at various positions in the sensing optical fiber to obtain a Brillouin gain spectrum;

[0076] S2. Perform forward or backward integration on the Brillouin gain spectrum at each position to obtain a forward integrated spectrum or a backward integrated spectrum; the integration formula is the above formulas (2) to (3).

[0077] S3. Find the frequency corresponding to the position with the maximum slope in the forward integrated spectrum or the backward integrated spectrum as the Brillouin frequency shift value at that position, and then obtain the Brillouin frequency shift value at each position in the sensing optical fiber.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A Brillouin frequency shift extraction device based on bidirectional integration, characterized in that: include: Narrow linewidth laser (1), a first coupler (2), a pulse modulator (4), an optical circulator (7), a sensing optical fiber (8), a polarization scrambler (10), a second coupler (13), a photodetector (14), a mixer (15), a signal generator (16), and a data acquisition and processing system (20); The laser light emitted by the narrow linewidth laser (1) is divided into two beams by the first coupler (2), one beam is used as detection light and is converted into pulse light by a pulse modulator (4), the pulse light enters the sensing optical fiber (8) after passing through an optical circulator (7), and the back Brillouin scattering signal generated in the sensing optical fiber (8) is emitted by the optical circulator and enters an input end of the second coupler (13); the other beam is used as reference light and enters the other input end of the second coupler (13) after passing through a polarization scrambler (10); The beat frequency signal output from the output end of the second coupler (13) is received by the photoelectric detector (14) for photoelectric conversion, and the generated electrical signal is mixed with the radio frequency signal generated by the signal generator (16) in the mixer (15), and the low-frequency signal obtained by mixing is sent to the data acquisition and processing system (20); The data acquisition and processing system (20) is used to acquire the low-frequency signal obtained by mixing to obtain the Brillouin gain spectrum at each position, and then perform forward integration and / or backward integration processing on the Brillouin gain spectrum at each position, find the frequency corresponding to the position with the maximum slope in the forward integration spectrum or the backward integration spectrum, and use it as the Brillouin frequency shift value at the position, thereby obtaining the Brillouin frequency shift value at each position in the sensing optical fiber.

2. The Brillouin frequency shift extraction device based on bidirectional integration according to claim 1, characterized in that: It also includes an amplifier (17), a bandpass filter (18), and a detector (19). The low-frequency signal obtained by mixing is amplified, filtered, and detected by the amplifier (17), the bandpass filter (18), and the detector (19) in sequence, and then sent to the data acquisition and processing system (20).

3. The Brillouin frequency shift extraction device based on bidirectional integration according to claim 1, characterized in that: It also includes a first optical attenuator (3) and a second optical attenuator (9); The first optical attenuator (3) is arranged before the pulse modulator (4) and is used to attenuate the intensity of the laser light entering the pulse modulator (4); The second optical attenuator (9) is arranged in the reference light path and is used to attenuate the intensity of the reference light.

4. The Brillouin frequency shift extraction device based on bidirectional integration according to claim 1, characterized in that: It also includes a pulse amplifier (5) and an erbium-doped fiber amplifier (11); the pulse amplifier (5) is arranged after the pulse modulator (4) and is used to amplify the pulse light output by the pulse modulator (4); The erbium-doped fiber amplifier (11) is arranged between the optical circulator (7) and the second coupler (13) and is used to amplify the backward Brillouin scattering signal generated in the sensing optical fiber (8).

5. The Brillouin frequency shift extraction device based on bidirectional integration according to claim 4, characterized in that: Also includes: A first optical filter (6) and a second optical filter (12); The first optical filter (6) is arranged at the output end of the pulse amplifier (5) and is used to filter the pulse light; The second optical filter (12) is arranged at the output end of the erbium-doped optical fiber amplifier (11) and is used to filter the backward Brillouin scattering signal generated in the sensing optical fiber (8).

6. The Brillouin frequency shift extraction device based on bidirectional integration according to claim 1, characterized in that: The narrow linewidth laser (1) has a central wavelength of 1550 nm and a linewidth of 3 kHz.

7. A Brillouin frequency shift extraction method based on bidirectional integration, implemented based on a Brillouin frequency shift extraction device based on bidirectional integration according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1, collecting Brillouin signals at various positions in the sensing optical fiber to obtain a Brillouin gain spectrum; S2, performing forward or backward integration on the Brillouin gain spectrum at each position to obtain a forward integrated spectrum or a backward integrated spectrum; S3. Find the frequency corresponding to the position with the maximum slope in the forward integrated spectrum or the backward integrated spectrum as the Brillouin frequency shift value at that position, and then obtain the Brillouin frequency shift value at each position in the sensing optical fiber.

8. The Brillouin frequency shift extraction method based on bidirectional integration according to claim 7, characterized in that: The integral formula is: ； ； Where G1(v) represents the amplitude corresponding to frequency v in the forward integrated spectrum, G2(v) represents the amplitude corresponding to frequency v in the backward integrated spectrum, g(x) represents the amplitude at frequency x in the Brillouin gain spectrum, and v1 and v2 are the initial and end frequencies of the Brillouin gain spectrum.

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