A distributed acoustic sensing phase demodulation method and system

Abstract

The present invention relates to a distributed acoustic sensing phase demodulation method and system, the method comprising the following steps: dividing a beam of continuous light into a detection light and a local oscillator light, modulating the detection light into a Gray complementary light pulse sequence, attenuating the local oscillator light to obtain an attenuated local oscillator light; causing the Gray complementary light pulse sequence to generate a backscattered Rayleigh signal, causing the attenuated local oscillator light to interfere with the backscattered Rayleigh signal to obtain an interference signal, high-pass filtering the interference signal to obtain a filtered interference signal; decoding the filtered interference signal, demodulating the decoded signal to obtain phase information caused by vibration. The distributed acoustic sensing phase demodulation method of the present invention improves the signal-to-noise ratio in phase demodulation.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to a distributed acoustic sensing phase demodulation method and system. Background Art

[0002] Distributed acoustic sensing has attracted widespread attention due to its excellent potential in many fields such as seismic wave measurement, oil exploration, transportation, border security, etc.; optical fiber as a sensor has low sensing loss, can overcome harsh environments such as corrosion, flammability, explosion, high temperature and high pressure, and has good characteristics of optical fiber distribution and extension. It is currently the most powerful medium for information transmission, and a large amount of sensing data can be easily transmitted. The sensing unit of distributed optical fiber sensing is the optical fiber itself. By demodulating the backscattered signal, the optical fiber can be converted into a large number of virtual sensors. Therefore, once the optical fiber is laid, a large number of sensors are deployed at the same time without considering the power supply of each sensor. Based on the above characteristics, distributed optical fiber sensing has become a hot spot in the field of optical fiber sensing at home and abroad.

[0003] In the field of distributed fiber optic sensing applications, phase-sensitive optical time-domain reflectometry By demodulating the phase information carried in the backscattered Rayleigh light wave, the vibration signal can be restored. Therefore, how to improve the signal-to-noise ratio of the demodulated phase signal has always been the focus of research. In common single-pulse systems, the phase information can be demodulated using a 3*3 phase demodulation algorithm. However, due to the fact that the modulation signal is a single pulse, the signal-to-noise ratio of the system is limited by the energy of the optical pulse. Therefore, the signal-to-noise ratio in phase demodulation in the prior art needs to be improved. Summary of the invention

[0004] In view of this, it is necessary to provide a distributed acoustic sensing phase demodulation method and system to solve the problem of low signal-to-noise ratio in phase demodulation in the prior art.

[0005] The present invention provides a distributed acoustic sensing phase demodulation method, comprising the following steps:

[0006] Splitting a beam of continuous light into a detection light and a local oscillator light, modulating the detection light into a Gray complementary light pulse sequence, and attenuating the local oscillator light to obtain attenuated local oscillator light;

[0007] The Gray complementary optical pulse sequence generates a backscattered Rayleigh signal, the attenuated local oscillator light interferes with the backscattered Rayleigh signal to obtain an interference signal, and the interference signal is high-pass filtered to obtain a filtered interference signal;

[0008] The filtered interference signal is decoded, and the decoded signal is demodulated to obtain phase information caused by the vibration.

[0009] Furthermore, the detection light is modulated into a Gray complementary optical pulse sequence, which specifically includes biasing the Gray complementary sequence to obtain a positive unipolar coding sequence, and modulating the detection light into a Gray complementary optical pulse sequence according to the unipolar coding sequence.

[0010] Further, the detection light is modulated into a Gray complementary light pulse sequence according to the unipolar coding sequence, specifically including: according to the unipolar coding sequence C=[C1, C2, ... C M+1 ], modulating the detection light into a Gray complementary light pulse sequence Among them, C p is the amplitude of the pth pulse, τ is the pulse width, is the M+1th Gray complementary optical pulse sequence, w s is the angular frequency of the optical pulse sequence, and i is an imaginary unit.

[0011] Further, the attenuated local oscillator light is interfered with the backscattered Rayleigh signal to obtain a filtered interference signal, which specifically includes: interfering the attenuated local oscillator light with the backscattered Rayleigh signal to obtain three interference signals, the phase difference of the three interference signals is 120°, and the expression of the three interference signals is:

[0012]

[0013] Where r represents the response coefficient of the photodetector, As is the amplitude of the backscattered Rayleigh signal, and A is l The amplitude of the local oscillator light signal, Δw is the frequency shift of the AOM, p is the pth bit of the coding sequence, q = p + 1, The phase difference between the Rayleigh scattering carried by the p-th pulse and the q-th pulse.

[0014] Further, the interference signal is subjected to high-pass filtering to obtain a filtered interference signal, specifically comprising: performing high-pass filtering on the three interference signals to obtain three filtered interference signals y code (t) = C*I(t), where

[0015] Further, decoding the filtered interference signal specifically includes decoding the filtered interference signal using a decoding formula, wherein the decoding formula is:

[0016]

[0017] Among them, L is the length of the encoding sequence, y i Indicates that the single pulse heterodyne structure is from the 3*3 coupler i end

[0018] The signal output from the port, i=1,2,3, represents correlation operation, * represents convolution operation, y 11 ,y 21 ,y 31 ,y 41 They respectively represent the filtered interference signals corresponding to the four groups of Gray complementary optical pulse sequences.

[0019] The present invention also provides a distributed acoustic sensing phase demodulation system, comprising a 1*2 coupler, an acousto-optic modulator, an arbitrary waveform generator, an attenuator, a circulator, a sensing optical fiber, a 3*3 coupler, a high-pass filter and a digital processing unit;

[0020] The 1*2 coupler is used to divide a beam of continuous light into a detection light and a local oscillator light; the acousto-optic modulator and the arbitrary waveform generator are used to modulate the detection light into a Gray complementary optical pulse sequence; the attenuator is used to attenuate the local oscillator light to obtain the attenuated local oscillator light;

[0021] The circulator and the sensing optical fiber are used to make the Gray complementary optical pulse sequence generate a backscattered Rayleigh signal; the 3*3 coupler causes the attenuated local oscillator light to interfere with the backscattered Rayleigh signal to obtain an interference signal, and the high-pass filter is used to perform high-pass filtering on the interference signal to obtain a filtered interference signal;

[0022] The digital processing unit is used to decode the filtered interference signal and demodulate the decoded signal to obtain phase information caused by vibration.

[0023] Furthermore, the acousto-optic modulator and the arbitrary waveform generator modulate the detection light into a Gray complementary light pulse sequence, specifically including: the arbitrary waveform generator output is biased by the Gray complementary sequence to obtain a positive unipolar coding sequence, and the acousto-optic modulator is driven by the unipolar coding sequence, and the acousto-optic modulator modulates the detection light into a Gray complementary light pulse sequence.

[0024] Furthermore, there are three high-pass filters, and the high-pass filters are used to perform high-pass filtering on the interference signal to obtain the filtered interference signal, specifically including: the three high-pass filters respectively perform high-pass filtering on the three interference signals to obtain the three filtered interference signals y code (t) = C*I(t), where r represents the response coefficient of the photodetector, As is the amplitude of the backscattered Rayleigh signal, A l The amplitude of the local oscillator optical signal, τ is the pulse width.

[0025] Furthermore, the distributed acoustic sensing phase demodulation system also includes three photodetectors, and the three photodetectors are used to convert the interference signal output from the 3*3 coupler into an electrical signal.

[0026] Compared with the prior art, the beneficial effects of the present invention include: dividing a beam of continuous light into detection light and local oscillator light, modulating the detection light into a Gray complementary light pulse sequence, attenuating the local oscillator light, and obtaining attenuated local oscillator light; causing the Gray complementary light pulse sequence to generate a backscattered Rayleigh signal, causing the attenuated local oscillator light to interfere with the backscattered Rayleigh signal to obtain an interference signal, high-pass filtering the interference signal to obtain a filtered interference signal; decoding the filtered interference signal, demodulating the decoded signal to obtain phase information caused by vibration; and improving the signal-to-noise ratio in phase demodulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of the flow of the distributed acoustic sensing phase demodulation method provided by the present invention;

[0028] Figure 2 A schematic diagram of a 32-bit Gray complementary sequence provided by the present invention;

[0029] Figure 3 Schematic diagram of 4 groups of equivalent unipolar sequences provided by the present invention;

[0030] Figure 4 A schematic diagram of the structure of the distributed acoustic sensing phase demodulation system provided by the present invention.

[0031] Figure numerals: 1-laser light source; 2-1*2 coupler; 3-arbitrary waveform generator; 4-acousto-optic modulator; 5-optical circulator; 6-sensing optical fiber; 7-3*3 coupler; 8-photodetector 1; 9-photodetector 2; 10-photodetector 3; 11-analog high-pass filter 1; 12-analog high-pass filter 2; 13-analog high-pass filter 3; 14-digital processing unit. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0033] Example 1

[0034] The embodiment of the present invention provides a distributed acoustic sensing phase demodulation method, and its flow chart is as follows: Figure 1 As shown, the method comprises the following steps:

[0035] S1, dividing a beam of continuous light into a detection light and a local oscillator light, modulating the detection light into a Gray complementary light pulse sequence, and attenuating the local oscillator light to obtain attenuated local oscillator light;

[0036] S2, causing the Gray complementary optical pulse sequence to generate a backscattered Rayleigh signal, causing the attenuated local oscillator light to interfere with the backscattered Rayleigh signal to obtain an interference signal, and performing high-pass filtering on the interference signal to obtain a filtered interference signal;

[0037] S3. Decode the filtered interference signal, and demodulate the decoded signal to obtain phase information caused by the vibration.

[0038] In a specific embodiment, the continuous light emitted by the ultra-narrow linewidth continuous wave laser is divided into two beams after passing through a 1*2 coupler, the upper branch is called the detection light, and the lower branch is called the local oscillator light;

[0039] Preferably, modulating the detection light into a Gray complementary optical pulse sequence specifically includes biasing the Gray complementary sequence to obtain a positive unipolar coding sequence, and modulating the detection light into a Gray complementary optical pulse sequence according to the unipolar coding sequence;

[0040] In a specific embodiment, the detection light passes through an acousto-optic modulator (AOM) with a frequency shift of Δw, and an arbitrary waveform generator (AWG) outputs four groups of equivalent positive unipolar coding sequences C1, C2, C3, and C4 obtained by biasing the Gray complementary sequence. The AOM is driven by these four groups of unipolar coding sequences to modulate the continuous light (detection light) passing through into a Gray complementary optical pulse sequence, thereby obtaining four groups of specifically coded optical pulse sequences;

[0041] Preferably, the detection light is modulated into a Gray complementary light pulse sequence according to the unipolar coding sequence, specifically comprising: according to the unipolar coding sequence C=[C1, C2, ... C M+1 ], modulating the detection light into a Gray complementary light pulse sequence Among them, C p is the amplitude of the pth pulse, τ is the pulse width, is the M+1th Gray complementary optical pulse sequence, w s is the angular frequency of the optical pulse train, i is the imaginary unit, and t is the time;

[0042] In a specific embodiment, the positive unipolar coding sequence can be expressed as C = [C1, C2, ... C M+1 ], therefore, the M+1th optical pulse sequence can be expressed as C p is the amplitude of the pth pulse, τ is the pulse width;

[0043] Schematic diagram of 32-bit Gray complementary sequence, such as Figure 2 As shown, Figure 2 For the simulation, sequence A and sequence B are a pair of Golay complementary sequences;

[0044] Schematic diagram of 4 equivalent unipolar sequences, such as Figure 3 As shown, Figure 3 The four groups of equivalent unipolar sequences obtained after the 32-bit Gray complementary sequence A and sequence B are biased and numbered as C1, C2, C3 and C4;

[0045] Preferably, the attenuated local oscillator light is interfered with the backscattered Rayleigh signal to obtain a filtered interference signal, which specifically includes causing the attenuated local oscillator light to interfere with the backscattered Rayleigh signal to obtain three interference signals, wherein the phase difference of the three interference signals is 120°, and the expression of the three interference signals is:

[0046]

[0047] Where r represents the response coefficient of the photodetector, As is the amplitude of the backscattered Rayleigh signal, and A is l The amplitude of the local oscillator optical signal, Δw is the frequency shift of the AOM, p is the pth bit of the coding sequence, q=p+1, q is the qth bit of the coding sequence, The phase difference between the Rayleigh scattering carried by the p-th pulse and the q-th pulse.

[0048] In a specific embodiment, the Gray complementary optical pulse sequence passes through port 1 of the circulator, and then enters the sensing optical fiber through port 2 of the circulator to generate a backscattered Rayleigh signal. The backscattered Rayleigh signal passes through port 3 of the circulator and interferes with the local oscillator light attenuated by the attenuator in the 3*3 coupler. The interference signal is divided into three signals with a phase difference of 120°, which enter three photodetectors (PDs) respectively and are converted into electrical signals. The output ports of the 3*3 coupler are numbered as ports 1, 2, and 3 from top to bottom, and the output signal of port 1 is

[0049]

[0050] Preferably, the interference signal is subjected to high-pass filtering to obtain a filtered interference signal, which specifically includes: high-pass filtering the three interference signals to obtain three filtered interference signals y code (t) = C*I(t), where

[0051] After filtering with an analog high-pass filter, the filtered interference signal can be expressed as

[0052]

[0053] I(t) is the interference signal of the single pulse heterodyne system, expressed as

[0054]

[0055] Preferably, decoding the filtered interference signal specifically includes decoding the filtered interference signal using a decoding formula, wherein the decoding formula is:

[0056]

[0057] Among them, L is the length of the encoding sequence, y i Represents the signal output from the i-port of the 3*3 coupler by the single pulse heterodyne structure, i=1,2,3, represents correlation operation, * represents convolution operation, y 11 ,y 21 ,y 31 ,y 41 They represent the filtered interference signals corresponding to the four groups of Gray complementary optical pulse sequences respectively;

[0058] In a specific embodiment, after processing the corresponding filtered interference signals, 4 sets of Gray complementary optical pulse sequences will generate 3 signals with a phase difference of 120° at the output port of the 3*3 coupler; the 4 sets of signals output from port 1 and after high-pass filtering are numbered y 11 ,y 21 ,y 31 ,y 41 ; Decode these 4 signals using the following formula:

[0059]

[0060] Where L is the length of the coding sequence, y1 represents the signal output from port 1 of the 3*3 coupler by the single pulse heterodyne structure, Indicates correlation operation, * indicates convolution operation; similarly, the signals after decoding at port 2 and port 3 are 2Ly2 and 2Ly3, respectively, where y2 and y3 represent the signals output from port 2 and port 3 of the 3*3 coupler by the single pulse heterodyne structure; the decoded 3-way signals are demodulated using the 3*3 algorithm to demodulate the phase information caused by vibration;

[0061] Compared with the traditional single-pulse 3*3 demodulation scheme, the interference signal amplitude output by the scheme described in the embodiment of the present invention is expanded by 2L times, the intensity signal-to-noise ratio is higher, and the phase signal-to-noise ratio is proportional to the intensity signal-to-noise ratio, and the demodulated phase signal has a higher signal-to-noise ratio.

[0062] Example 2

[0063] The embodiment of the present invention further provides a distributed acoustic sensing phase demodulation system, comprising a 1*2 coupler, an acousto-optic modulator, an arbitrary waveform generator, an attenuator, a circulator, a sensing optical fiber, a 3*3 coupler, a high-pass filter and a digital processing unit;

[0064] The 1*2 coupler is used to divide a beam of continuous light into a detection light and a local oscillator light; the acousto-optic modulator and the arbitrary waveform generator are used to modulate the detection light into a Gray complementary optical pulse sequence; the attenuator is used to attenuate the local oscillator light to obtain the attenuated local oscillator light;

[0065] The circulator and the sensing optical fiber are used to make the Gray complementary optical pulse sequence generate a backscattered Rayleigh signal; the 3*3 coupler causes the attenuated local oscillator light to interfere with the backscattered Rayleigh signal to obtain an interference signal, and the high-pass filter is used to perform high-pass filtering on the interference signal to obtain a filtered interference signal;

[0066] The digital processing unit is used to decode the filtered interference signal and demodulate the decoded signal to obtain phase information caused by vibration.

[0067] Preferably, the acousto-optic modulator and the arbitrary waveform generator modulate the detection light into a Gray complementary light pulse sequence, specifically including: the output of the arbitrary waveform generator is biased by the Gray complementary sequence to obtain a positive unipolar coding sequence, and the acousto-optic modulator is driven by the unipolar coding sequence, and the acousto-optic modulator modulates the detection light into a Gray complementary light pulse sequence.

[0068] Preferably, there are three high-pass filters, and the high-pass filters are used to perform high-pass filtering on the interference signal to obtain the filtered interference signal, which specifically includes: the three high-pass filters respectively perform high-pass filtering on the three interference signals to obtain the three filtered interference signals y code (t) = C*I(t), where r represents the response coefficient of the photodetector, As is the amplitude of the backscattered Rayleigh signal, A l The amplitude of the local oscillator optical signal, τ is the pulse width.

[0069] Preferably, the distributed acoustic sensing phase demodulation system further includes three photodetectors, and the three photodetectors are used to convert the interference signal output from the 3*3 coupler into an electrical signal;

[0070] In a specific embodiment, the distributed acoustic sensing phase demodulation system has a structural diagram as shown in FIG. Figure 4As shown, it includes a laser light source 1, a coupler 2, an arbitrary waveform generator 3, an acousto-optic modulator 4, an optical circulator 5, a sensing optical fiber 6, a 3*3 coupler 7, a photodetector 1 8, a photodetector 2 9, a photodetector 3 10, an analog high-pass filter 1 11, an analog high-pass filter 2 12, an analog high-pass filter 3 13 and a digital processing unit 14;

[0071] The laser light source 1 is a narrow line width light source, and the arbitrary waveform generator 3 emits a specified coded electrical pulse sequence. In specific implementation, the Gray complementary sequence is used to encode the continuous light; the Gray complementary sequence is a bipolar code, and the light pulse cannot be negative, so the bipolar code needs to be converted into a unipolar code first;

[0072] Through the bias method, one bipolar code sequence can be converted into two unipolar code sequences, so one set of bipolar Gray complementary sequences can be converted into four unipolar code sequences; an arbitrary waveform generator is used to output four unipolar code sequences, and the emission interval time of each unipolar code sequence is T, T is greater than or equal to the round-trip time of the detection light in the sensing fiber, and four unipolar code sequences constitute one cycle, and one cycle time is 4T;

[0073] It should be noted that the Rayleigh scattered light and local oscillator light reflected by the detection light interfere with each other in the 3*3 coupler; the three output ports of the 3*3 coupler output signals with a phase difference of 120°; the three photodetectors (PDs) convert the three optical signals into electrical signals respectively; and the analog high-pass filter filters out the inter-symbol interference caused by pulse coding in the interference signal.

[0074] The present invention discloses a distributed acoustic sensing phase demodulation method and system. The method comprises the following steps: dividing a beam of continuous light into a detection light and a local oscillator light, modulating the detection light into a Gray complementary light pulse sequence, attenuating the local oscillator light to obtain the attenuated local oscillator light; causing the Gray complementary light pulse sequence to generate a backscattered Rayleigh signal, causing the attenuated local oscillator light to interfere with the backscattered Rayleigh signal to obtain an interference signal, high-pass filtering the interference signal to obtain a filtered interference signal; decoding the filtered interference signal, demodulating the decoded signal to obtain phase information caused by vibration, and improving the signal-to-noise ratio in phase demodulation.

[0075] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A distributed acoustic sensing phase demodulation method, characterized in that: The following steps are involved: Splitting a beam of continuous light into a detection light and a local oscillator light, modulating the detection light into a Gray complementary light pulse sequence, and attenuating the local oscillator light to obtain attenuated local oscillator light; The Gray complementary optical pulse sequence generates a backscattered Rayleigh signal, the attenuated local oscillator light interferes with the backscattered Rayleigh signal to obtain an interference signal, and the interference signal is high-pass filtered to obtain a filtered interference signal; Decoding the filtered interference signal, and demodulating the decoded signal to obtain phase information caused by the vibration; Modulating the detection light into a Gray complementary optical pulse sequence, specifically comprising: biasing the Gray complementary sequence to obtain a positive unipolar coding sequence, wherein one set of bipolar Gray complementary optical pulse sequences can be converted into four unipolar coding sequences, and modulating the detection light into a Gray complementary optical pulse sequence according to the unipolar coding sequence; The attenuated local oscillator light is interfered with the backscattered Rayleigh signal to obtain a filtered interference signal, specifically comprising: interfering the attenuated local oscillator light with the backscattered Rayleigh signal to obtain three interference signals, the phase difference of the three interference signals is 120°, and the expressions of the three interference signals are: in, r represents the response coefficient of the photodetector, As The amplitude of the backscattered Rayleigh signal, A l The amplitude of the local oscillator light signal, Δ w is the frequency shift of the AOM, p The coding sequence p Bit, q = p +1, For the p The pulse and q The Rayleigh scattering produced by the two pulses carries a phase difference.

2. The distributed acoustic sensing phase demodulation method according to claim 1, characterized in that: Modulating the detection light into a Gray complementary light pulse sequence according to the unipolar coding sequence specifically includes: , modulate the probe light into a Gray complementary light pulse sequence ,in, For the p The amplitude of the pulse, τ is the pulse width, For the M +1-bit Gray complementary optical pulse sequence, is the angular frequency of the optical pulse train, i Is an imaginary unit.

3. The distributed acoustic sensing phase demodulation method according to claim 1, characterized in that: The interference signal is subjected to high-pass filtering to obtain a filtered interference signal, specifically comprising: performing high-pass filtering on the three interference signals to obtain three filtered interference signals. ,in, .

4. The distributed acoustic sensing phase demodulation method according to claim 1, characterized in that: Decoding the filtered interference signal specifically includes decoding the filtered interference signal using a decoding formula, wherein the decoding formula is: in, L is the encoding sequence length, y i Represents a single pulse heterodyne structure from a 3*3 coupler i end The output signal of the port, , represents correlation operation, * represents convolution operation, y 11 , y 21 , y 31 , y 41 They respectively represent the filtered interference signals corresponding to the four groups of Gray complementary optical pulse sequences.

5. A distributed acoustic sensing phase demodulation system, characterized in that: Includes 1*2 coupler, acousto-optic modulator, arbitrary waveform generator, attenuator, circulator, sensing fiber, 3*3 coupler, high-pass filter and digital processing unit; The 1*2 coupler is used to divide a beam of continuous light into a detection light and a local oscillator light; the acousto-optic modulator and the arbitrary waveform generator are used to modulate the detection light into a Gray complementary optical pulse sequence; the attenuator is used to attenuate the local oscillator light to obtain the attenuated local oscillator light; The circulator and the sensing optical fiber are used to make the Gray complementary optical pulse sequence generate a backscattered Rayleigh signal; the 3*3 coupler causes the attenuated local oscillator light to interfere with the backscattered Rayleigh signal to obtain an interference signal, and the high-pass filter is used to perform high-pass filtering on the interference signal to obtain a filtered interference signal; The digital processing unit is used to decode the filtered interference signal and demodulate the decoded signal to obtain phase information caused by the vibration; Modulating the detection light into a Gray complementary optical pulse sequence, specifically comprising: biasing the Gray complementary sequence to obtain a positive unipolar coding sequence, wherein one set of bipolar Gray complementary optical pulse sequences can be converted into four unipolar coding sequences, and modulating the detection light into a Gray complementary optical pulse sequence according to the unipolar coding sequence; The attenuated local oscillator light is interfered with the backscattered Rayleigh signal to obtain a filtered interference signal, specifically comprising: interfering the attenuated local oscillator light with the backscattered Rayleigh signal to obtain three interference signals, the phase difference of the three interference signals is 120°, and the expressions of the three interference signals are: in, r represents the response coefficient of the photodetector, As The amplitude of the backscattered Rayleigh signal, A l The amplitude of the local oscillator light signal, Δ w is the frequency shift of the AOM, p The coding sequence p Bit, q = p +1, For the p The pulse and q The Rayleigh scattering produced by the two pulses carries a phase difference.

6. The distributed acoustic sensing phase demodulation system according to claim 5, characterized in that: The acousto-optic modulator and the arbitrary waveform generator modulate the detection light into a Gray complementary optical pulse sequence, specifically comprising: the output of the arbitrary waveform generator is biased by the Gray complementary sequence to obtain a positive unipolar coding sequence, and the acousto-optic modulator is driven by the unipolar coding sequence, and the acousto-optic modulator modulates the detection light into a Gray complementary optical pulse sequence.

7. The distributed acoustic sensing phase demodulation system according to claim 5, characterized in that: There are three high-pass filters, and the high-pass filters are used to perform high-pass filtering on the interference signal to obtain the filtered interference signal. Specifically, the three high-pass filters respectively perform high-pass filtering on the three interference signals to obtain the three filtered interference signals. ,in, , r represents the response coefficient of the photodetector, As The amplitude of the backscattered Rayleigh signal, A l The amplitude of the local oscillator optical signal, , τ is the pulse width.

8. The distributed acoustic sensing phase demodulation system according to claim 7, characterized in that: The device also includes three photodetectors, which are used to convert interference signals output from the 3*3 coupler into electrical signals.

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