Phase Demodulation Method and System

Abstract

This application relates to the field of fiber optic sensing technology, and particularly to a phase demodulation method and system. Among them, the phase demodulation method includes: obtaining a first discrete signal corresponding to a first beat frequency signal and a second discrete signal corresponding to a second beat frequency signal; the first beat frequency signal is generated by the interference between a first backward Rayleigh scattering optical signal and a local oscillator optical signal, and the second beat frequency signal is generated by the interference between a second backward Rayleigh scattering optical signal and a local oscillator optical signal; determining a first parameter and a second parameter based on a phase demodulation algorithm, the first discrete signal, and the second discrete signal; calculating the differential phase of a phase-sensitive optical time domain reflectometry fiber optic sensing system based on the first parameter and the second parameter. By using the first discrete signal and the second discrete signal with a first time interval, the differential phase between two different positions in the phase-sensitive optical time domain reflectometry fiber optic sensing system can be directly demodulated, and the frequency noise value brought by the laser can be directly eliminated, improving the signal-to-noise ratio of the system.

Description

Technical Field

[0001] This application relates to the technical field of fiber optic sensing, and particularly relates to a phase demodulation method and system. Background Art

[0002] Based on the phase-sensitive optical time domain reflectometry (Φ-OTDR) fiber optic sensing system, it can perform distributed multi-point real-time monitoring on tiny signals over a long distance. It has the characteristics of high sensitivity, large spatial dynamic range, and high positioning accuracy. Therefore, it has broad market application prospects in aspects such as health monitoring of large facilities, industrial production process detection, perimeter security, pipeline protection, and ocean engineering.

[0003] Currently, the phase demodulation of the phase-sensitive optical time domain reflectometry fiber optic sensing system is mainly based on hardware phase demodulation schemes including phase-generated carrier, phase demodulation based on a 3×3 coupler, I / Q demodulation, etc. The phase-generated carrier method requires the introduction of a phase modulator and a demodulator, which increases the complexity and cost of the system, and depends on precise phase modulation. Any modulation error will affect the final demodulation accuracy. For the phase demodulation method based on a 3×3 coupler, the demodulation accuracy is limited by the manufacturing error of the coupler, which may lead to inaccurate phase demodulation. Due to the use of multiple couplers and other optical components, the system loss is large, and the optical intensity signal may weaken, affecting the demodulation effect. I / Q demodulation requires complex circuit design, including quadrature modulators, photoelectric balanced detectors, and high-performance signal processing circuits, which increases the complexity and cost of the system. Usually, it needs to process a large amount of data in real time, has high requirements for the computing power and processing speed of the system, and is very sensitive to the phase noise in the system. Especially the phase noise of the light source and the phase jitter in the system will both cause demodulation errors. Therefore, the existing demodulation methods have problems such as high cost, complex system, large noise, and large amount of calculation, seriously affecting the practical application and industrialization of the sensing system.

[0004] In a conventional Φ-OTDR system, it is necessary to record and at two positions to demodulate the digital difference, which has relatively high requirements for the data storage of the hardware demodulation system. Moreover, the frequency drift brought by the laser in the Φ-OTDR system will cause frequency noise in the optical signal, resulting in the drift of the demodulated phase obtained by the system, destroying the integrity of the measured signal, causing waveform distortion, reducing the signal-to-noise ratio of the system, and making the information such as the position and frequency of the obtained disturbance event inaccurate.

[0005] Therefore, there is an urgent need to propose a new phase demodulation method to overcome the above technical problems. Summary of the Invention

[0006] The embodiments of the present application provide a phase demodulation method and system. By using the first backward Rayleigh scattering optical signal and the second backward Rayleigh scattering optical signal generated by the same optical pulse, the phases at two different positions can be obtained simultaneously, and the differential phase can be directly obtained by taking the difference. Moreover, the frequency noise value brought by the laser can be eliminated to improve the signal-to-noise ratio of the system.

[0007] In some embodiments, a phase demodulation method is provided. The phase demodulation method is applied to a phase demodulation system, and the phase demodulation system includes a phase-sensitive optical time domain reflectometry (OTDR) fiber sensing system. The phase-sensitive OTDR fiber sensing system outputs the first backward Rayleigh scattering optical signal and the second backward Rayleigh scattering optical signal generated by the same optical pulse. The generation time of the first backward Rayleigh scattering optical signal is the first time, and the generation time of the second backward Rayleigh scattering optical signal is the second time. There is a first time interval between the first time and the second time. The phase demodulation method includes: obtaining the first discrete signal corresponding to the first beat frequency signal and the second discrete signal corresponding to the second beat frequency signal; the first beat frequency signal is generated by the interference between the first backward Rayleigh scattering optical signal and the local oscillator optical signal, and the second beat frequency signal is generated by the interference between the second backward Rayleigh scattering optical signal and the local oscillator optical signal; based on the phase demodulation algorithm, the first discrete signal and the second discrete signal, determining the first parameter and the second parameter; based on the first parameter and the second parameter, calculating the differential phase of the phase-sensitive OTDR fiber sensing system.

[0008] By using the phase demodulation method provided by the embodiments of the present application, through the first discrete signal and the second discrete signal with a first time interval output by the phase-sensitive OTDR fiber sensing system, the differential phase between two different positions in the phase-sensitive OTDR fiber sensing system can be directly demodulated according to the first discrete signal and the second discrete signal, reducing the requirement for the system storage capacity and improving the demodulation efficiency of the differential phase. Moreover, during the demodulation process, the frequency noise value brought by the laser can be directly eliminated to improve the signal-to-noise ratio of the system.

[0009] Optionally, the first backward Rayleigh scattering optical signal is as follows in the first formula;

[0010] The first formula is:

[0011] ;

[0012] The second backward Rayleigh scattering optical signal is as follows in the second formula;

[0013] The second formula is:

[0014] ;

[0015] Wherein, is the pulse interval, is the order of the optical pulse, is the first phase added during the process of generating the first backward Rayleigh scattering optical signal, is the second phase added during the process of generating the second backward Rayleigh scattering optical signal, represents the imaginary part, is the first amplitude of the first backward Rayleigh scattering optical signal at time is the second amplitude of the second backward Rayleigh scattering optical signal at time is the first frequency, is the second frequency.

[0016] Optionally, the phase-sensitive optical time domain reflectometry fiber optic sensing system includes a first acousto-optic modulator and a second acousto-optic modulator;

[0017] The first backward Rayleigh scattering optical signal is obtained based on the first optical pulse modulated by the first acousto-optic modulator, and the second backward Rayleigh scattering optical signal is obtained based on the second optical pulse modulated by the first acousto-optic modulator and the second acousto-optic modulator;

[0018] , is the central angular frequency of the laser light source, is the frequency shift center of the first acousto-optic modulator;

[0019] , is the frequency shift center of the second acousto-optic modulator.

[0020] Optionally, the phase-sensitive optical time domain reflectometry fiber optic sensing system further includes a laser, and the laser is configured to output optical pulses;

[0021] The local oscillator optical signal is as follows in the third formula;

[0022] The third formula is:

[0023] ;

[0024] Wherein, is the amplitude of the local oscillator optical signal, is the initial phase of the local oscillator optical signal, is the frequency noise value of the laser at time

[0025] Optionally, the phase-sensitive optical time domain reflectometry fiber sensing system further includes a 3 dB coupler, and the phase demodulation system further includes a photoelectric balanced detector and a digital acquisition card. The 3 dB coupler includes a first output port and a second output port; obtaining the first discrete signal corresponding to the first beat frequency signal and the second discrete signal corresponding to the second beat frequency signal includes:

[0026] Based on the 3 dB coupler, the local oscillator optical signal, the first backward Rayleigh scattering optical signal, and the second backward Rayleigh scattering optical signal, determine the first optical intensity output from the first output port and the second optical intensity output from the second output port;

[0027] Based on the photoelectric balanced detector, determine the total voltage signal corresponding to the first beat frequency signal and the second beat frequency signal; the first beat frequency signal is obtained by extracting the AC signal with the first center frequency from the first optical intensity and the second optical intensity, and the second beat frequency signal is obtained by extracting the AC signal with the second center frequency from the first optical intensity and the second optical intensity; the first center frequency is , and the second center frequency is ;

[0028] Based on the digital acquisition card, collect the total discrete signal corresponding to the total voltage signal;

[0029] Based on the total discrete signal, determine the first discrete signal and the second discrete signal.

[0030] Optionally, the total discrete signal includes a first initial voltage signal with the first center frequency and a second initial voltage signal with the second center frequency; based on the total discrete signal, determining the first discrete signal and the second discrete signal includes:

[0031] Based on the band-pass filtering technique, the first center frequency, and the second center frequency, respectively extract the first initial voltage signal and the second initial voltage signal from the total discrete signal;

[0032] Based on the mixing technique, the low-pass filtering technique, the first initial voltage signal, and the second initial voltage signal, determine the first voltage sub-signal, the second voltage sub-signal, the third voltage sub-signal, and the fourth voltage sub-signal; the first discrete signal includes the first voltage sub-signal and the second voltage sub-signal, and the second discrete signal includes the third voltage sub-signal and the fourth voltage sub-signal; the first voltage sub-signal is obtained by mixing the first initial voltage signal with and then performing low-pass filtering; the second voltage sub-signal is obtained by mixing the first initial voltage signal with and then performing low-pass filtering; the third voltage sub-signal is obtained by mixing the second initial voltage signal with and then performing low-pass filtering; the fourth voltage sub-signal is obtained by mixing the second initial voltage signal with and then performing low-pass filtering.

[0033] Optionally, based on the phase demodulation algorithm, the first discrete signal, and the second discrete signal, determining the first parameter and the second parameter includes:

[0034] Normalize the first voltage sub-signal, the second voltage sub-signal, the third voltage sub-signal, and the fourth voltage sub-signal to determine the first normalized signal, the second normalized signal, the third normalized signal, and the fourth normalized signal; the first voltage sub-signal corresponds to the first normalized signal, the second voltage sub-signal corresponds to the second normalized signal, the third voltage sub-signal corresponds to the third normalized signal, and the fourth voltage sub-signal corresponds to the fourth normalized signal;

[0035] Based on the first normalized signal , the second normalized signal , the third normalized signal , and the fourth normalized signal , calculate the first parameter according to the following fourth formula , and calculate the second parameter according to the following fifth formula ;

[0036] The fourth formula is:

[0037] ;

[0038] The fifth formula is:

[0039] ;

[0040] Where , is the speed of light, is the refractive index of light with a light frequency of in the sensing optical fiber, is the first time interval.

[0041] Optionally, based on the first parameter and the second parameter, calculating the differential phase of the phase-sensitive optical time domain reflectometry fiber optic sensing system includes:

[0042] Based on the first parameter and the second parameter, calculate the phase differential according to the following sixth formula ;

[0043] Integrate and restore the phase differential to obtain the differential phase of the phase-sensitive optical time domain reflectometry fiber optic sensing system;

[0044] The sixth formula is:

[0045] 。

[0046] Optionally, based on the first parameter and the second parameter, calculating the differential phase of the phase-sensitive optical time domain reflectometry fiber optic sensing system includes:

[0047] Based on the first parameter and the second parameter, calculate the tangent parameter according to the following seventh formula ;

[0048] Calculate the differential phase of the phase-sensitive optical time domain reflectometry (OTDR) fiber sensing system according to the following eighth formula ;

[0049] The seventh formula is:

[0050] ;

[0051] The eighth formula is:

[0052] ;

[0053] Wherein, is the third parameter, and the third parameter is determined by the unwrapping algorithm. In some embodiments, a phase demodulation system is provided, including: a phase-sensitive optical time domain reflectometry (OTDR) fiber sensing system and a data processing module; the phase-sensitive optical time domain reflectometry (OTDR) fiber sensing system is configured to output a first backward Rayleigh scattering optical signal and a second backward Rayleigh scattering optical signal generated by the same optical pulse, the generation time of the first backward Rayleigh scattering optical signal is the first time, the generation time of the second backward Rayleigh scattering optical signal is the second time, and there is a first time interval between the first time and the second time; the data processing module is communicatively connected to the phase-sensitive optical time domain reflectometry (OTDR) fiber sensing system; the data processing module is configured to obtain a first discrete signal corresponding to the first beat frequency signal and a second discrete signal corresponding to the second beat frequency signal; the first beat frequency signal is generated by the interference between the first backward Rayleigh scattering optical signal and the local oscillator optical signal, and the second beat frequency signal is generated by the interference between the second backward Rayleigh scattering optical signal and the local oscillator optical signal; based on the phase demodulation algorithm, the first discrete signal and the second discrete signal, determine the first parameter and the second parameter; based on the first parameter and the second parameter, calculate the differential phase of the phase-sensitive optical time domain reflectometry (OTDR) fiber sensing system.

[0054] It can be understood that for the beneficial effects that can be achieved by the technical solution provided by the above-mentioned phase demodulation system, reference can be made to the beneficial effects in the phase demodulation method and any of its optional embodiments, which will not be elaborated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the technical solutions of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0056] Figure 1It is a structural block diagram of the phase demodulation system provided by the embodiment of the present application;

[0057] Figure 2 It is a structural diagram of the phase demodulation system provided by the embodiment of the present application;

[0058] Figure 3 It is a timing diagram of the first optical pulse and the second optical pulse provided by the embodiment of the present application;

[0059] Figure 4 It is a flowchart of the phase demodulation method provided by the embodiment of the present application.

[0060] Reference numerals:

[0061] 100, phase-sensitive optical time domain reflectometry fiber optic sensing system; 101, narrow linewidth laser; 102, first fiber optic coupler; 103, first acousto-optic modulator; 104, second fiber optic coupler; 105, filter; 106, second acousto-optic modulator; 107, delay fiber; 108, first optical amplifier; 109, second optical amplifier; 110, fiber optic circulator; 1101, first port; 1102, second port; 1103, third port; 111, sensing fiber; 112, third optical amplifier; 113, third fiber optic coupler; 114, photoelectric balanced detector; 115, digital acquisition card;

[0062] 200, data processing module; 201, computer; 202, mobile phone. Detailed implementation manners

[0063] Next, the technical solutions in the embodiments of the present application will be clearly described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0064] Hereinafter, terms such as "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present application, unless otherwise specified, the meaning of "a plurality" is two or more.

[0065] In addition, in the present application, orientation terms such as "upper", "lower", "inner", "outer", etc. are defined relative to the orientation of the components shown in the accompanying drawings. It should be understood that these directional terms are relative concepts, and they are used for relative description and clarification, and they may change accordingly with the change of the orientation of the components placed in the accompanying drawings.

[0066] For the convenience of understanding the technical solution of the application, the related technologies involved in the present application will be described below first.

[0067] The phase-sensitive optical time domain reflectometry (OTDR) fiber sensing system can perform distributed multi-point real-time monitoring of weak signals over a long distance. It has the characteristics of high sensitivity, large spatial dynamic range, and high positioning accuracy. Therefore, it has broad market application prospects in the health monitoring of large facilities, industrial production process detection, perimeter security, pipeline protection, ocean engineering, etc.

[0068] Currently, the phase demodulation of interferometric fiber sensing systems (including phase-sensitive OTDR fiber sensing systems) is mainly based on hardware phase demodulation schemes including phase-generated carrier, phase demodulation based on a 3×3 coupler, I / Q demodulation, etc.

[0069] The phase-generated carrier method (Phase-Generated Carrier, abbreviated as PGC) is a common phase demodulation method used in interferometric fiber sensing systems. The phase-generated carrier method modulates the phase of light by applying a high-frequency carrier to the interference signal, enabling the extraction of the originally difficult-to-directly-demodulate phase information through spectral transformation. Since the phase-generated carrier method requires the introduction of a phase modulator and a demodulator, it increases the complexity and cost of the system, and depends on precise phase modulation. Any modulation error will affect the final demodulation accuracy.

[0070] The phase demodulation method based on the 3×3 coupler structure is a phase demodulation technology widely used in fiber interferometers. By utilizing the special structure of the 3×3 fiber coupler, it can divide the fiber interference signal into three paths and achieve phase demodulation through mathematical calculations. This method is usually used in systems such as fiber optic gyroscopes (FOG) and has high demodulation accuracy and stability. However, the demodulation accuracy of the phase demodulation method based on the 3×3 coupler structure is limited by the manufacturing error of the coupler, which may lead to inaccurate phase demodulation. Due to the use of multiple couplers and other optical components, the system loss is large, and the optical intensity signal may weaken, affecting the demodulation effect.

[0071] I / Q demodulation (In-phase and Quadrature Demodulation) is a common method for extracting useful information from modulated signals. It is widely used in communication systems, radars, software-defined radios, fiber optic sensors, and other fields. However, I / Q demodulation requires complex circuit designs, including quadrature modulators, optoelectronic balanced detectors, and high-performance signal processing circuits, which increases the complexity and cost of the system. It usually requires real-time processing of a large amount of data, has high requirements for the computing power and processing speed of the system, and is very sensitive to phase noise in the system. In particular, the phase noise of the light source and the phase jitter within the system can both cause demodulation errors.

[0072] Therefore, existing phase demodulation methods have problems such as high cost, complex systems, large noise, and large computational amounts, which seriously affect the practical application and industrialization of phase-sensitive optical time domain reflectometry fiber optic sensing systems.

[0073] Moreover, in a conventional Φ-OTDR system, the and at two positions need to be recorded to demodulate the digital difference, which has high requirements for the data storage of the hardware demodulation system. The phase demodulation method provided by the embodiments of the present application can simultaneously obtain the phases at two different positions through the optical pulse a and optical pulse b generated by the same optical pulse, and can directly perform difference to obtain the phase difference .

[0074] Figure 1 This is the structural block diagram of the phase demodulation system provided by the embodiments of the present application.

[0075] To solve the above technical problems, the embodiments of the present application provide a phase demodulation system, including: a phase-sensitive optical time domain reflectometry fiber optic sensing system 100 and a data processing module 200. The phase-sensitive optical time domain reflectometry fiber optic sensing system 100 is configured to output a first backward Rayleigh scattering optical signal and a second backward Rayleigh scattering optical signal generated by the same optical pulse. The generation time of the first backward Rayleigh scattering optical signal is the first time, and the generation time of the second backward Rayleigh scattering optical signal is the second time. There is a first time interval between the first time and the second time. The data processing module 200 is communicatively connected to the phase-sensitive optical time domain reflectometry fiber optic sensing system 100. The data processing module 200 is configured to obtain a first discrete signal corresponding to the first beat frequency signal and a second discrete signal corresponding to the second beat frequency signal. The first beat frequency signal is generated by the interference between the first backward Rayleigh scattering optical signal and the local oscillator optical signal, and the second beat frequency signal is generated by the interference between the second backward Rayleigh scattering optical signal and the local oscillator optical signal. Based on the first beat frequency signal and the second beat frequency signal, the differential phase of the phase-sensitive optical time domain reflectometry fiber optic sensing system 100 is demodulated.

[0076] Figure 2 The structural diagram of the phase demodulation system provided by the embodiment of the present application.

[0077] Optionally, the phase-sensitive optical time domain reflectometry fiber sensing system 100 includes: a narrow linewidth laser 101, a first optical fiber coupler 102, a first acousto-optic modulator 103, a second optical fiber coupler 104, a filter 105, a second acousto-optic modulator 106, a delay fiber 107, a first optical amplifier 108, a second optical amplifier 109, an optical fiber circulator 110, a sensing fiber 111, a third optical amplifier 112, a third optical fiber coupler 113, a photoelectric balanced detector 114, and a digital acquisition card 115. The data processing module 200 is communicatively connected to the digital acquisition card 115. The narrow linewidth laser 101 is configured to output an initial laser. The splitting ratio of the first optical fiber coupler 102 is 90:10. The first acousto-optic modulator 103 is configured to modulate the initial laser output by the narrow linewidth laser 101 into an optical pulse a with a first optical frequency The splitting ratio of the second optical fiber coupler 104 is 50:50. The filter 105 is configured to eliminate the noise in the optical pulse a. The second acousto-optic modulator 106 is configured to modulate the optical pulse a into an optical pulse b with a second optical frequency The delay fiber 107 is configured to adjust a first time interval between the optical pulse a and the optical pulse b . The first optical amplifier 108 is configured to amplify the energy of the optical pulse b to be the same as the energy of the optical pulse a. The second optical amplifier 109 is configured to amplify the energy of the optical pulse a and the optical pulse b. The optical fiber circulator 110 includes a first port 1101, a second port 1102, and a third port 1103. The sensing fiber 111 is configured to input the optical pulse a to generate a first backward Rayleigh scattering optical signal, and input the optical pulse b to generate a second backward Rayleigh scattering optical signal. The third optical amplifier 112 is configured to amplify the energy of the first backward Rayleigh scattering optical signal and the second backward Rayleigh scattering optical signal. The splitting ratio of the third optical fiber coupler 113 is 50:50, that is, a 3db coupler. The photoelectric balanced detector 114 is configured to receive the optical signal output by the third optical fiber coupler 113 and convert it into a total voltage signal. The digital acquisition card 115 is configured to acquire the total voltage signal output by the photoelectric balanced detector 114 as a total discrete signal.

[0078] Figure 3 The timing diagram of the first optical pulse and the second optical pulse provided by the embodiment of the present application.

[0079] Specifically, the narrow linewidth laser 101 outputs an initial laser d (the optical frequency is ). The initial laser d is divided into two parts by the first optical fiber coupler 102. One part is the local oscillator light (the local oscillator light signal c), and the remaining part is modulated into the first optical pulse (i.e., the optical pulse a, the optical frequency is , the pulse width is w, and the optical pulse repetition frequency is f). The optical pulse a passes through the second optical fiber coupler 104, and 50% of the optical pulse a enters the second optical amplifier 109. The remaining 50% of the optical pulse a successively passes through the filter 105 and the second acousto-optic modulator 106 and is modulated into a second optical pulse (i.e., optical pulse b, the optical frequency is , the pulse width is w, and the optical pulse repetition frequency is f). The optical pulse b passes through the delay optical fiber 107, so that there is a first time interval between the optical pulse b and the optical pulse a (the timing diagram of the optical pulse a and the optical pulse b is as Figure 3 shown). The optical pulse b then enters the first optical amplifier 108 to amplify the energy of the optical pulse b to be equal to the energy of the optical pulse a. After the optical pulse b enters the second optical fiber coupler 104 again, 50% of the optical pulse b enters the second optical amplifier 109 after the optical pulse a. After the optical pulse a and the optical pulse b are amplified to the required energy, they enter the optical fiber circulator 110 through the first port 1101 of the optical fiber circulator 110, and then are output through the second port 1102 of the optical fiber circulator 110 and transmitted to the sensing optical fiber 111 to generate a first backward Rayleigh scattering optical signal (corresponding to the optical pulse a) and a second backward Rayleigh scattering optical signal (corresponding to the optical pulse b). Then, it enters the optical fiber circulator 110 through the second port 1102 of the optical fiber circulator 110 and is transmitted to the third optical amplifier 112 through the third port 1103 of the optical fiber circulator 110 for further amplification to increase the power of the first backward Rayleigh scattering optical signal and the second backward Rayleigh scattering optical signal. The backward Rayleigh scattering signals (the first backward Rayleigh scattering optical signal and the second backward Rayleigh scattering optical signal) and the local oscillator optical signal pass through the third optical fiber coupler 113 for beat frequency interference. The two beat frequency interference signals (the first beat frequency signal and the second beat frequency signal) output by the third optical fiber coupler 113 are converted into electrical signals (the first voltage signal and the second voltage signal) by the optoelectronic balanced detector 114. The electrical signals are collected by the digital acquisition card 115 to obtain discrete signals (the first discrete signal and the second discrete signal), and then the phase demodulation is performed by the data processing module 200 to obtain the differential phase of the phase-sensitive optical time domain reflectometry fiber sensing system 100.

[0080] Exemplarily, in combination with Figure 3As shown, optical pulse a1 and optical pulse b1 are generated by the same optical pulse d1, optical pulse a2 and optical pulse b2 are generated by the same optical pulse d2. There is a first time interval δt between the start time 0 of optical pulse a1 and the start time δt of optical pulse b1. There is a first time interval δt between the end time w of optical pulse a1 and the end time δt + w of optical pulse b1. There is a first time interval δt between the start time T of optical pulse a2 and the start time T + δt of optical pulse b2. There is a first time interval δt between the end time T + w of optical pulse a2 and the end time T + δt + w of optical pulse b2.

[0081] Specifically, the third optical fiber coupler 113 is a 3dB coupler. The 3dB coupler includes a first input port, a second input port, a first output port, and a second output port. The first input port is configured to input a first backward Rayleigh scattering optical signal and a second backward Rayleigh scattering optical signal. The second input port is configured to input a local oscillator optical signal. The first output port is configured to output a first optical intensity. The second output port is configured to output a second optical intensity. The photoelectric balanced detector 114 is configured to receive the first optical intensity and the second optical intensity output by the 3dB coupler, and is further configured to determine a total voltage signal corresponding to a first beat frequency signal and a second beat frequency signal. The first beat frequency signal is obtained by extracting an alternating current signal with a first center frequency from the first optical intensity and the second optical intensity. The second beat frequency signal is obtained by extracting an alternating current signal with a second center frequency from the first optical intensity and the second optical intensity. The first center frequency is , and the second center frequency is . The digital acquisition card 115 is communicatively connected to the photoelectric balanced detector 114. The digital acquisition card 115 is configured to obtain the total voltage signal and is further configured to acquire a total discrete signal corresponding to the total voltage signal.

[0082] Specifically, the data processing module 200 is further configured to determine a first discrete signal and a second discrete signal based on the total discrete signal.

[0083] Optionally, as Figure 2 shown, the data processing module 200 includes but is not limited to one or more of a computer 201, a mobile phone 202, a tablet computer (not shown in the figure), and a mobile wearable device (not shown in the figure), as long as the data processing module 200 can implement the above functions.

[0084] Figure 4 This is a flowchart of the phase demodulation method provided by the embodiment of the present application.

[0085] Combined with Figure 1 and Figure 2 the phase demodulation system shown, the embodiment of the present application further provides a phase demodulation method. The phase demodulation method is applied to the phase demodulation system. AsFigure 4 As shown, the phase demodulation method includes steps S100 to S300, specifically as follows:

[0086] Step S100: Obtain the first discrete signal corresponding to the first beat frequency signal and the second discrete signal corresponding to the second beat frequency signal; the first beat frequency signal is generated by the interference between the first backward Rayleigh scattered optical signal and the local oscillator optical signal, and the second beat frequency signal is generated by the interference between the second backward Rayleigh scattered optical signal and the local oscillator optical signal.

[0087] Specifically, in combination with Figure 2 as shown, the formula between the first backward Rayleigh scattered optical signal generated by the optical pulse a passing through the sensing optical fiber 111 and the time t is as shown in formula (1) below, and the formula between the second backward Rayleigh scattered optical signal generated by the optical pulse b passing through the sensing optical fiber 111 and the time t is as shown in formula (2) below.

[0088] (1).

[0089] (2).

[0090] Among them, is the first detection optical amplitude of the first optical pulse (optical pulse a), is the first detection optical amplitude of the second optical pulse (optical pulse b), is the time after the detection pulse is emitted, is the time delay corresponding to the i-th Rayleigh scattering center, is the detection optical pulse width, is the backward Rayleigh scattering coefficient of the i-th Rayleigh scattering center, , is the distance of the i-th Rayleigh scattering center from the input end of the sensing optical fiber, is the optical fiber attenuation coefficient. Among them, is the speed of light, is the optical repetition frequency, and is the refractive index of light with the optical repetition frequency in the sensing optical fiber.

[0091] Specifically, the time corresponding to t = 0 is the time when the optical pulse enters the sensing optical fiber.

[0092] .

[0093] , is the central angular frequency of the laser light source (such as the initial laser of the narrow linewidth laser 101 provided in the above embodiment), is the frequency shift center of the first acousto-optic modulator 103, , is the frequency shift center of the second acousto-optic modulator 106.

[0094] As can be seen from the above (1), at a certain moment the obtained backward Rayleigh scattering optical signal is the interference result of the scattered light of all Rayleigh scattering centers within the pulse, and the signal at moment corresponds to the information of the detection optical fiber position . Among them, 0 ≤ <T, where T is the pulse interval.

[0095] Assume that the optical repetition frequency (i.e., the repetition frequency of optical pulses) is f, T = 1 / f, and the backward Rayleigh scattering optical signals generated by the Nth optical pulse a and optical pulse b through the sensing optical fiber are respectively as follows (3) and (4):

[0096] (3).

[0097] (4).

[0098] Optionally, the first backward Rayleigh scattering optical signal is as follows in the first formula;

[0099] The first formula is:

[0100] ;

[0101] The second backward Rayleigh scattering optical signal is as follows in the second formula;

[0102] The second formula is:

[0103] ;

[0104] Among them, is the pulse interval, is the order of the optical pulse, is the first additional phase in the process of generating the first backward Rayleigh scattering optical signal, is the second additional phase in the process of generating the second backward Rayleigh scattering optical signal, represents the imaginary part, is the first amplitude of the first backward Rayleigh scattering optical signal at moment is the second amplitude of the second backward Rayleigh scattering optical signal at moment is the first frequency, is the second frequency.

[0105] In this embodiment, the complex amplitude is used to represent the first backward Rayleigh scattering optical signal and the second backward Rayleigh scattering optical signal, so as to facilitate the subsequent demodulation of the phase.

[0106] Specifically, for the sake of easy understanding, the above first formula is taken as (5), and the second formula is taken as (6) to continue the above description.

[0107] Optionally, combined with Figure 2 As shown, the phase-sensitive optical time domain reflectometry fiber optic sensing system 100 includes a first acousto-optic modulator 103 and a second acousto-optic modulator 106. The first backward Rayleigh scattering optical signal is obtained based on the first optical pulse (optical pulse a) modulated by the first acousto-optic modulator 103, and the second backward Rayleigh scattering optical signal is obtained based on the second optical pulse (optical pulse b) modulated by the first acousto-optic modulator and the second acousto-optic modulator. , is the central angular frequency of the laser light source, is the frequency shift center of the first acousto-optic modulator; , is the frequency shift center of the second acousto-optic modulator.

[0108] In this embodiment, the first optical pulse is obtained by modulating the initial laser based on the first acousto-optic modulator 103, and part of the first optical pulse is used to obtain the second optical pulse by modulating the first optical pulse based on the second acousto-optic modulator 106. Then, the remaining part of the first optical pulse passes through the sensing optical fiber 111 to obtain the first backward Rayleigh scattering optical signal, and the second optical pulse passes through the sensing optical fiber 111 to obtain the second backward Rayleigh scattering optical signal. Therefore includes the frequency shift center of the first acousto-optic modulator, includes the frequency shift center of the first acousto-optic modulator and the frequency shift center of the second acousto-optic modulator.

[0109] Specifically, the Φ-OTDR system is a coherent detection system, which requires that the laser source has a stable frequency output and good monochromaticity at the same time. The frequency drift brought by the laser will seriously reduce the sensing performance of the Φ-OTDR system, cause the demodulated phase obtained by the system to drift, damage the integrity of the measured signal, cause waveform distortion, reduce the signal-to-noise ratio of the system, and make the information such as the position and frequency of the obtained disturbance event inaccurate. The frequency drift of the laser belongs to a slow-varying signal with a low change frequency, which will seriously interfere with the monitoring ability of the system for low-frequency signals.

[0110] In order to suppress the influence of laser frequency drift and frequency noise on the system, in the related art, it is proposed to measure the frequency drift of the laser by using an auxiliary interferometer to compensate for the frequency drift in the sensing path. However, this increases the system complexity, and the use and setting of the reference interferometer have a great influence on the suppression effect. Alternatively, in the related art, the method of quadratic difference is used to compensate for the frequency drift. However, in this related art, it is necessary to find a compensation signal in an area without interference near the perturbation area, and the selection of the compensation signal has a great influence on the compensation effect.

[0111] Therefore, in the phase demodulation method provided by the embodiments of the present application, through the mixing technology in the phase demodulation algorithm, four mixed signals (i.e., the first voltage sub-signal, the second voltage sub-signal, the third voltage sub-signal, and the fourth voltage sub-signal obtained by mixing the first initial voltage signal and the second initial voltage signal in the total output voltage) are respectively obtained. The first discrete signal includes the first voltage sub-signal and the second voltage sub-signal, and the second discrete signal includes the third voltage sub-signal and the fourth voltage sub-signal). Thus, the frequency noise value of the laser can be directly eliminated, and then the differential phase that is not affected by the laser noise can be directly demodulated, improving the accuracy of the demodulated differential phase and the monitoring ability of the system for low-frequency signals.

[0112] Optionally, the phase-sensitive optical time-domain reflectometry fiber sensing system further includes a laser, and the laser is configured to output optical pulses;

[0113] local oscillator optical signal as the following third formula;

[0114] The third formula is:

[0115] ;

[0116] Wherein, is the amplitude of the local oscillator optical signal, is the initial phase of the local oscillator optical signal, is the frequency noise value of the laser at time

[0117] Specifically, for the convenience of understanding, the above third formula is taken as (7) to continue the above description.

[0118] Exemplarily, the laser is as Figure 2 the narrow linewidth laser 101 shown in

[0119] Specifically, as can be seen from the above third formula, the local oscillator optical signal contains the frequency noise value of the laser at time

[0120] Optionally, in combination with Figure 2As shown, the phase-sensitive optical time domain reflectometry (OTDR) fiber sensing system 100 further includes a 3 dB coupler (the third fiber coupler 113), and the phase demodulation system further includes a photoelectric balanced detector 114 and a digital acquisition card 115. The 3 dB coupler includes a first output port and a second output port. Step S100 includes steps S101 to S104, which are specifically as follows:

[0121] Step S101: Based on the 3 dB coupler, the local oscillator optical signal, the first backward Rayleigh scattering optical signal, and the second backward Rayleigh scattering optical signal, determine the first optical intensity output from the first output port and the second optical intensity output from the second output port.

[0122] Optionally, the first optical intensity is as follows (8):

[0123] (8);

[0124] Wherein, as shown in the following (9), as shown in the following (10).

[0125] (9);

[0126] (10).

[0127] The second optical intensity is as follows (11):

[0128] (11);

[0129] Wherein, as shown in the following (12), as shown in the following (13).

[0130] (12);

[0131] (13).

[0132] Wherein, is the first amplitude of the first backward Rayleigh scattering light at time is the frequency noise value of the laser at time is the phase at time

[0133] Specifically, , , and are deduced as follows:

[0134] (9).

[0135] (10).

[0136] (12).

[0137] (13).

[0138] Specifically, in the above (9), (10), (12), and (13), represents conjugation. For example, is 's conjugate. Combining the above , , and all have three terms. The first two terms represent the DC part of the light intensity, and the third term is the AC part of the light intensity, that is, the beat frequency signal. Therefore, the AC signal with a center frequency of in the first light intensity and the second light intensity is extracted to obtain the first beat frequency signal, and the AC signal with a center frequency of in the first light intensity and the second light intensity is extracted to obtain the second beat frequency signal.

[0139] Step S102, based on the optoelectronic balanced detector, determine the total voltage signal corresponding to the first beat frequency signal and the second beat frequency signal; the first beat frequency signal is obtained by extracting the AC signal with a center frequency of the first center frequency in the first light intensity and the second light intensity, and the second beat frequency signal is obtained by extracting the AC signal with a center frequency of the second center frequency in the first light intensity and the second light intensity. The first center frequency is , and the second center frequency is .

[0140] Optionally, the first beat frequency signal is as follows (14):

[0141] (14);

[0142] The second beat frequency signal is as follows (15):

[0143] (15);

[0144] Among them, is the first amplitude of the first backward Rayleigh scattering light at time , and is the phase at time

[0145] Step S103, based on the digital acquisition card, collect the total discrete signal corresponding to the total voltage signal.

[0146] Step S104: Determine a first discrete signal and a second discrete signal based on the total discrete signal.

[0147] Optionally, the total discrete signal includes a first initial voltage signal having a first center frequency and a second initial voltage signal having a second center frequency; Step S104 includes Step S1041 and Step S1042, which are specifically as follows:

[0148] Step S1041: Extract the first initial voltage signal and the second initial voltage signal in the total discrete signal respectively based on the band - pass filtering technique, the first center frequency, and the second center frequency.

[0149] Specifically, the total discrete signal is as shown in (16) below:

[0150] (16).

[0151] Wherein, is the first initial voltage signal, is the second initial voltage signal.

[0152] Specifically, the first initial voltage signal is as shown in (17) below:

[0153] (17).

[0154] The second initial voltage signal is as shown in (18) below:

[0155] (18).

[0156] Step S1042: Determine a first voltage sub - signal, a second voltage sub - signal, a third voltage sub - signal, and a fourth voltage sub - signal based on the mixing technique, the low - pass filtering technique, the first initial voltage signal, and the second initial voltage signal; the first discrete signal includes the first voltage sub - signal and the second voltage sub - signal, and the second discrete signal includes the third voltage sub - signal and the fourth voltage sub - signal; the first voltage sub - signal is obtained by mixing the first initial voltage signal with and then performing low - pass filtering; the second voltage sub - signal is obtained by mixing the first initial voltage signal with and then performing low - pass filtering; the third voltage sub - signal is obtained by mixing the second initial voltage signal with and then performing low - pass filtering; the fourth voltage sub - signal is obtained by mixing the second initial voltage signal with and then performing low - pass filtering.

[0157] In this embodiment, the first initial voltage signal and the second initial voltage signal in the total discrete signal are extracted based on the first center frequency and the second center frequency, so as to facilitate obtaining the first voltage sub-signal and the second voltage sub-signal after mixing and low-pass filtering according to the first initial voltage signal, and obtaining the third voltage sub-signal and the fourth voltage sub-signal after mixing and low-pass filtering according to the second initial voltage signal. Thus, it is convenient to eliminate the frequency noise value of the laser according to the first voltage sub-signal, the second voltage sub-signal, the third voltage sub-signal and the fourth voltage sub-signal, and then the differential phase not affected by the laser noise can be directly demodulated, improving the accuracy of the demodulated differential phase and the monitoring ability of the system for low-frequency signals.

[0158] Specifically, the first voltage sub-signal is as shown in the following (19):

[0159] (19).

[0160] The second voltage sub-signal is as shown in the following (20):

[0161] (20).

[0162] The third voltage sub-signal is as shown in the following (21):

[0163] (21).

[0164] The fourth voltage sub-signal is as shown in the following (22):

[0165] (22).

[0166] In this embodiment, by determining the first discrete signal and the second discrete signal, the differential phase of the phase-sensitive optical time domain reflectometry fiber sensing system is demodulated according to the first discrete signal and the second discrete signal.

[0167] Specifically, corresponding to the position , corresponding to the position . According to the relationship between the time 0 ≤ <T and the detection position , the first discrete signal (as shown in the following (23) and (24)) and the second discrete signal (as shown in the following (25) and (26)) are collected. The first discrete signal includes the first voltage sub-signal ( , as shown in the following (23)) and the second voltage sub-signal ( , as shown in (24) below, the second discrete signal includes a third voltage sub-signal ( , as shown in (25) below) and a fourth voltage sub-signal ( , as shown in (26) below).

[0168] (23).

[0169] (24).

[0170] (25).

[0171] (26).

[0172] Wherein, , is the first time interval.

[0173] Step S200, based on the phase demodulation algorithm, the first discrete signal and the second discrete signal, determine the first parameter and the second parameter.

[0174] Optionally, step S200 includes step S201 and step S202, specifically as follows:

[0175] Step S201, normalize the first voltage sub-signal, the second voltage sub-signal, the third voltage sub-signal and the fourth voltage sub-signal to determine the first normalized signal, the second normalized signal, the third normalized signal and the fourth normalized signal; the first voltage sub-signal corresponds to the first normalized signal, the second voltage sub-signal corresponds to the second normalized signal, the third voltage sub-signal corresponds to the third normalized signal, and the fourth voltage sub-signal corresponds to the fourth normalized signal.

[0176] Specifically, step S201 includes S2011 to step S2014, specifically as follows:

[0177] Step S2011, based on the first voltage sub-signal and the second voltage sub-signal , calculate the first normalization parameter .

[0178] Specifically, calculate the first normalization parameter as shown in (27) below:

[0179] (27).

[0180] Step S2012, use the first normalization parameter to convert the amplitudes in the first voltage sub-signal and the second voltage sub-signal to 1. That is, divide the first voltage sub-signal by the first normalization parameter, and divide the second voltage sub-signal by the first normalization parameter.

[0181] Specifically, the normalized first voltage sub-signal (i.e., the first normalized signal ) is as shown in (28) below:

[0182] (28).

[0183] The normalized second voltage sub-signal (i.e., the second normalized signal ) is as shown in (29) below:

[0184] (29).

[0185] Step S2013: Calculate the second normalization parameter based on the third voltage sub-signal and the fourth voltage sub-signal .

[0186] Specifically, the calculation of the second normalization parameter is as shown in (30) below:

[0187] (30).

[0188] Step S2014: Use the second normalization parameter to convert the amplitudes in the third voltage sub-signal and the fourth voltage sub-signal to 1. That is, divide the third voltage sub-signal by the second normalization parameter, and divide the fourth voltage sub-signal by the second normalization parameter.

[0189] Specifically, the normalized third voltage sub-signal (i.e., the third normalized signal ) is as shown in (31) below:

[0190] (31).

[0191] The normalized fourth voltage sub-signal (i.e., the fourth normalized signal ) is as shown in (32) below:

[0192] (32).

[0193] In this embodiment, by normalizing the first voltage sub-signal, the second voltage sub-signal, the third voltage sub-signal, and the fourth voltage sub-signal, the amplitudes of the first voltage sub-signal, the second voltage sub-signal, the third voltage sub-signal, and the fourth voltage sub-signal are converted to 1, eliminating the influence of the amplitudes in the calculation.

[0194] Step S202: Based on the first normalized signal , the second normalized signal , and the third normalized signal and the fourth normalized signal , calculate the first parameter according to the following fourth formula , calculate the second parameter according to the following fifth formula ;

[0195] The fourth formula is:

[0196] ;

[0197] The fifth formula is:

[0198] ;

[0199] Wherein, , is the speed of light, is the refractive index of light with a light frequency of in the sensing optical fiber, is the first time interval.

[0200] Specifically, for the sake of understanding, the above fourth formula is taken as (33), and the fifth formula is taken as (34) to continue the above description.

[0201] Step S300, based on the first parameter and the second parameter, calculate the differential phase of the phase-sensitive optical time domain reflectometry fiber sensing system.

[0202] Optionally, step S300 includes step S301 and step S302, specifically as follows:

[0203] Step S301, based on the first parameter and the second parameter, calculate the phase differential according to the following sixth formula .

[0204] Step S302, integrate and restore the phase differential to obtain the differential phase of the phase-sensitive optical time domain reflectometry fiber sensing system ;

[0205] The sixth formula is:

[0206] .

[0207] Specifically, for the sake of understanding, the above sixth formula is taken as (35) to continue the above description.

[0208] Optionally, step S300 includes step S303 and step S304, specifically as follows:

[0209] Step S303, based on the first parameter and the second parameter, calculate the tangent parameter according to the following seventh formula .

[0210] The seventh formula is:

[0211] 。

[0212] Step S304, calculate the differential phase of the phase-sensitive optical time domain reflectometry (Φ-OTDR) fiber sensing system according to the following eighth formula 。

[0213] The eighth formula is:

[0214] 。

[0215] Where m is a third parameter, and the value of m is determined by the unwrapping algorithm.

[0216] Specifically, for the sake of easy understanding, the above seventh formula is taken as (36), and the eighth formula is taken as (37) to continue the above description.

[0217] By using the phase demodulation method provided in the embodiments of the present application, the first discrete signal and the second discrete signal with the first time interval output by the phase-sensitive optical time domain reflectometry (Φ-OTDR) fiber sensing system are used, so that the differential phase between two different positions in the phase-sensitive optical time domain reflectometry (Φ-OTDR) fiber sensing system can be directly demodulated according to the first discrete signal and the second discrete signal, reducing the requirement for the system storage capacity and improving the demodulation efficiency of the differential phase. Moreover, during the demodulation process, the frequency noise value brought by the laser can be directly eliminated to improve the signal-to-noise ratio of the system.

[0218] Specifically, for a conventional Φ-OTDR system, it is necessary to record the signals at two positions, and, in order to demodulate the digital difference, which requires a high data storage requirement for the hardware demodulation system. The phase demodulation method provided in the embodiments of the present application can simultaneously obtain the phases at two different positions, through the optical pulse a and the optical pulse b generated by the same optical pulse, and can directly perform the difference to obtain the phase difference, 。

[0219] Specifically, the phase demodulation method provided in the embodiments of the present application includes the above (1) to (35), or (1) to (34), (36), (37).

[0220] Corresponding to the embodiments of the foregoing phase demodulation method, the present application also provides embodiments of a phase demodulation system. The phase demodulation system includes: a phase-sensitive optical time domain reflectometry (OTDR) fiber sensing system and a data processing module; the phase-sensitive OTDR fiber sensing system is configured to output a first backward Rayleigh scattering optical signal and a second backward Rayleigh scattering optical signal generated by the same optical pulse, the generation time of the first backward Rayleigh scattering optical signal is a first time, the generation time of the second backward Rayleigh scattering optical signal is a second time, and there is a first time interval between the first time and the second time; the data processing module is communicatively connected to the phase-sensitive OTDR fiber sensing system; the data processing module is configured to obtain a first discrete signal corresponding to a first beat frequency signal and a second discrete signal corresponding to a second beat frequency signal; the first beat frequency signal is generated by interference between the first backward Rayleigh scattering optical signal and a local oscillator optical signal, and the second beat frequency signal is generated by interference between the second backward Rayleigh scattering optical signal and the local oscillator optical signal; based on a phase demodulation algorithm, the first discrete signal, and the second discrete signal, a first parameter and a second parameter are determined; based on the first parameter and the second parameter, the differential phase of the phase-sensitive OTDR fiber sensing system is calculated.

[0221] By using the phase demodulation system provided in the embodiments of the present application, the first discrete signal and the second discrete signal with a first time interval output by the phase-sensitive OTDR fiber sensing system are used, so that the differential phase between two different positions in the phase-sensitive OTDR fiber sensing system can be directly demodulated according to the first discrete signal and the second discrete signal, the requirement for the system storage capacity is reduced, and the demodulation efficiency of the differential phase is improved. Moreover, during the demodulation process, the frequency noise value brought by the laser can be directly eliminated to improve the signal-to-noise ratio of the system.

[0222] It should be noted that those skilled in the art will readily think of other implementation manners of the present application after considering the specification and practicing the application disclosed herein. The present application is intended to cover any variations, uses, or adaptations of the present application, which follow the general principles of the present application and include common general knowledge or conventional technical means in the technical field not disclosed in the present application. The specification and embodiments are only regarded as exemplary, and the true scope of the present application is pointed out by the claims.

[0223] It should be understood that the present application is not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present application is only limited by the appended claims.

Claims

1. A phase demodulation method, characterized in that, The phase demodulation method is applied to a phase demodulation system, which includes a phase-sensitive optical time domain reflectometry (OTDR) fiber sensing system. The phase-sensitive OTDR fiber sensing system outputs a first backward Rayleigh scattering optical signal and a second backward Rayleigh scattering optical signal generated by the same optical pulse. The generation time of the first backward Rayleigh scattering optical signal is the first time, and the generation time of the second backward Rayleigh scattering optical signal is the second time. There is a first time interval between the first time and the second time; The phase-sensitive OTDR fiber sensing system includes a first acousto-optic modulator and a second acousto-optic modulator; The first backward Rayleigh scattering optical signal is obtained based on a first optical pulse modulated by the first acousto-optic modulator, and the second backward Rayleigh scattering optical signal is obtained based on a second optical pulse modulated by the first acousto-optic modulator and the second acousto-optic modulator; The phase demodulation method includes: Obtaining a first discrete signal corresponding to a first beat frequency signal and a second discrete signal corresponding to a second beat frequency signal; the first beat frequency signal is generated by the interference between the first backward Rayleigh scattering optical signal and a local oscillator optical signal, and the second beat frequency signal is generated by the interference between the second backward Rayleigh scattering optical signal and the local oscillator optical signal; Determining a first parameter and a second parameter based on a phase demodulation algorithm, the first discrete signal, and the second discrete signal; Calculating the differential phase of the phase-sensitive OTDR fiber sensing system based on the first parameter and the second parameter; The phase-sensitive OTDR fiber sensing system further includes a 3 dB coupler. The phase demodulation system further includes a photoelectric balanced detector and a digital acquisition card. The 3 dB coupler includes a first output port and a second output port. The obtaining of the first discrete signal corresponding to the first beat frequency signal and the second discrete signal corresponding to the second beat frequency signal includes: Determining a first optical intensity output from the first output port and a second optical intensity output from the second output port based on the 3 dB coupler, the local oscillator optical signal, the first backward Rayleigh scattering optical signal, and the second backward Rayleigh scattering optical signal; Based on the optoelectronic balance detector, determine the total voltage signal corresponding to the first beat frequency signal and the second beat frequency signal; the first beat frequency signal is obtained by extracting an AC signal with a center frequency of a first center frequency from the first light intensity and the second light intensity, and the second beat frequency signal is obtained by extracting an AC signal with a center frequency of a second center frequency from the first light intensity and the second light intensity; the first center frequency is , and the second center frequency is ; Collecting a total discrete signal corresponding to the total voltage signal based on the digital acquisition card; Determining the first discrete signal and the second discrete signal based on the total discrete signal; The total discrete signal includes a first initial voltage signal having the first center frequency and a second initial voltage signal having the second center frequency. The determining of the first discrete signal and the second discrete signal based on the total discrete signal includes: Extracting the first initial voltage signal and the second initial voltage signal from the total discrete signal respectively based on a band-pass filtering technique, the first center frequency, and the second center frequency; Based on the mixing technology, low-pass filtering technology, the first initial voltage signal, and the second initial voltage signal, determine the first voltage sub-signal, the second voltage sub-signal, the third voltage sub-signal, and the fourth voltage sub-signal; the first discrete signal includes the first voltage sub-signal and the second voltage sub-signal, and the second discrete signal includes the third voltage sub-signal and the fourth voltage sub-signal; the first voltage sub-signal is obtained by mixing and low-pass filtering the first initial voltage signal with after mixing and low-pass filtering; the second voltage sub-signal is obtained by mixing and low-pass filtering the first initial voltage signal with after mixing and low-pass filtering; the third voltage sub-signal is obtained by mixing and low-pass filtering the second initial voltage signal with after mixing and low-pass filtering; the fourth voltage sub-signal is obtained by mixing and low-pass filtering the second initial voltage signal with after mixing and low-pass filtering; The determining of the first parameter and the second parameter based on the phase demodulation algorithm, the first discrete signal, and the second discrete signal includes: Normalize the first voltage sub-signal, the second voltage sub-signal, the third voltage sub-signal, and the fourth voltage sub-signal to determine a first normalized signal, a second normalized signal, a third normalized signal, and a fourth normalized signal; the first voltage sub-signal corresponds to the first normalized signal, the second voltage sub-signal corresponds to the second normalized signal, the third voltage sub-signal corresponds to the third normalized signal, and the fourth voltage sub-signal corresponds to the fourth normalized signal; Based on the first normalized signal , the second normalized signal , the third normalized signal and the fourth normalized signal , calculate the first parameter according to the following fourth formula , calculate the second parameter according to the following fifth formula ; The fourth formula is: ； The fifth formula is: ； Among them, the , the is the speed of light, the is the refractive index of light with a light frequency of in the sensing optical fiber, and the is the first time interval.

2. The phase demodulation method according to claim 1, wherein The first backward Rayleigh scattering optical signal The first formula below; The first formula is: ； The second backward Rayleigh scattering optical signal The following second formula; The second formula is: ； Among them, is the pulse interval, is the order of the optical pulses, is the first additional phase in the process of generating the first backward Rayleigh scattering optical signal, is the second additional phase in the process of generating the second backward Rayleigh scattering optical signal, represents the imaginary part, is the first amplitude of the first backward Rayleigh scattering optical signal at time is the second amplitude of the second backward Rayleigh scattering optical signal at time is the first frequency, is the second frequency.

3. The phase demodulation method according to claim 2, wherein , where the is the central angular frequency of the laser light source, and the is the frequency shift center of the first acousto-optic modulator; , the is the frequency shift center of the second acousto-optic modulator.

4. The phase demodulation method according to claim 1, wherein The phase-sensitive optical time domain reflectometry fiber optic sensing system further includes a laser, and the laser is configured to output the optical pulse; The local oscillator optical signal The following third formula; The third formula is: ； Among them, the is the amplitude of the local oscillator light, the is the initial phase of the local oscillator light, and the is the frequency noise value of the laser at the moment.

5. The phase demodulation method according to claim 1, characterized in that Calculating the differential phase of the phase-sensitive optical time domain reflectometry fiber optic sensing system based on the first parameter and the second parameter includes: Based on the first parameter and the second parameter, calculate the phase differential according to the following sixth formula ; Integrate and restore the phase differential to obtain the differential phase of the phase-sensitive optical time domain reflectometry fiber optic sensing system ; The sixth formula is: 。 6. The phase demodulation method according to claim 1, wherein Calculating the differential phase of the phase-sensitive optical time domain reflectometry fiber optic sensing system based on the first parameter and the second parameter includes: Calculate the tangent parameter according to the following seventh formula based on the first parameter and the second parameter ; Calculate the differential phase of the phase-sensitive optical time domain reflectometry (OTDR) fiber sensing system according to the following eighth formula ; The seventh formula is: ； The eighth formula is: ； Among them, the is the third parameter, and the third parameter is determined by the unwinding algorithm.

7. A phase demodulation system, characterized in that, Including: A phase-sensitive optical time domain reflectometry fiber optic sensing system and a data processing module as described in any one of claims 1 to 6; The phase-sensitive optical time domain reflectometry fiber optic sensing system is configured to output a first backward Rayleigh scattering optical signal and a second backward Rayleigh scattering optical signal generated by the same optical pulse. The generation time of the first backward Rayleigh scattering optical signal is a first time, the generation time of the second backward Rayleigh scattering optical signal is a second time, and there is a first time interval between the first time and the second time; the phase-sensitive optical time domain reflectometry fiber optic sensing system includes a first acousto-optic modulator and a second acousto-optic modulator; the first backward Rayleigh scattering optical signal is obtained based on the first optical pulse modulated by the first acousto-optic modulator, and the second backward Rayleigh scattering optical signal is obtained based on the second optical pulse modulated by the first acousto-optic modulator and the second acousto-optic modulator; The data processing module is communicatively connected to the phase-sensitive optical time domain reflectometry fiber optic sensing system; the data processing module is configured to obtain a first discrete signal corresponding to a first beat frequency signal and a second discrete signal corresponding to a second beat frequency signal; the first beat frequency signal is generated by interference between the first backward Rayleigh scattering optical signal and a local oscillator optical signal, and the second beat frequency signal is generated by interference between the second backward Rayleigh scattering optical signal and the local oscillator optical signal; Based on a phase demodulation algorithm, the first discrete signal, and the second discrete signal, determine a first parameter and a second parameter; based on the first parameter and the second parameter, calculate the differential phase of the phase-sensitive optical time domain reflectometry fiber optic sensing system.

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