Phase demodulation method and system

Abstract

The invention relates to the technical field of optical fiber sensing, in particular to a phase demodulation method and system. The phase demodulation method comprises the following steps: acquiring 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 a first backward Rayleigh scattering light signal and a local oscillation light signal, and the second beat frequency signal is generated by interference between a second backward Rayleigh scattering light signal and the local oscillation light signal; determining a first parameter and a second parameter based on a phase demodulation algorithm, the first discrete signal and the second discrete signal; and calculating the differential phase of the phase-sensitive optical time domain reflection fiber sensing system based on the first parameter and the second parameter. Through the first discrete signal and the second discrete signal with the first time interval, the differential phase between two different positions in the phase-sensitive optical time domain reflection fiber sensing system is directly demodulated, the frequency noise value brought by the laser can be directly eliminated, and the signal-to-noise ratio of the system is improved.

Description

Technical Field

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

[0002] The phase-sensitive optical time-domain reflectometry fiber optic sensing system is capable of distributed multi-point real-time monitoring of tiny signals over long distances. It has the characteristics of high sensitivity, large spatial dynamic range and high positioning accuracy. Therefore, it has broad market application prospects in large-scale facility health monitoring, industrial production process detection, perimeter security, pipeline protection, marine engineering, etc.

[0003] Currently, phase demodulation in phase-sensitive optical time-domain reflectometry fiber-optic sensing systems is primarily based on hardware-based phase demodulation schemes, including phase-generated carriers, phase demodulation based on a 3×3 coupler configuration, and I / Q demodulation. The phase-generated carrier method requires the introduction of a phase modulator and demodulator, increasing system complexity and cost. Furthermore, it relies on precise phase modulation, and any modulation error will affect the final demodulation accuracy. The phase demodulation method based on a 3×3 coupler is limited in demodulation accuracy by coupler manufacturing errors, potentially leading to inaccurate phase demodulation. Due to the use of multiple couplers and other optical components, system losses are significant, and optical signal intensity may be weakened, affecting demodulation performance. I / Q demodulation requires complex circuit design, including an orthogonal modulator, a photoelectrically balanced detector, and high-performance signal processing circuits, increasing system complexity and cost. It typically requires real-time processing of large amounts of data, placing high demands on the system's computing power and processing speed. It is also highly sensitive to phase noise within the system, particularly light source phase noise and phase jitter within the system, which can lead to demodulation errors. Consequently, existing demodulation methods suffer from high cost, system complexity, high noise levels, and computational complexity, seriously hindering the practical application and industrialization of sensing systems.

[0004] In conventional Φ-OTDR systems, two locations need to be recorded. and , which requires high data storage requirements for the hardware demodulation system. Furthermore, the frequency drift caused by the laser in the Φ-OTDR system can lead to frequency noise in the optical signal, causing the demodulated phase acquired by the system to drift, compromising the integrity of the measured signal, causing waveform distortion, and reducing the system's signal-to-noise ratio, resulting in inaccurate information such as the location and frequency of the disturbance event.

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

[0006] The present invention provides a phase demodulation method and system. Using a first backscattered Rayleigh light signal and a second backscattered Rayleigh light signal generated by the same optical pulse, the phases at two different locations can be simultaneously determined. Directly performing the differential phase analysis can yield the differential phase. This method also eliminates the frequency noise introduced by the laser, improving the system's signal-to-noise ratio.

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

[0008] The phase demodulation method provided in the embodiments of the present application uses a first discrete signal and a second discrete signal outputted by a phase-sensitive optical time-domain reflectometry fiber-optic sensor system at a first time interval to directly demodulate the differential phase between two different locations in the system. This reduces the system's storage capacity requirements and improves the demodulation efficiency of the differential phase. Furthermore, during the demodulation process, the frequency noise introduced by the laser can be directly eliminated, thereby improving the system's signal-to-noise ratio.

[0009] Optionally, the first backscattered Rayleigh light signal The first formula is as follows; The first formula is: ; The second backscattered Rayleigh light signal The second formula is as follows; The second formula is: ; in, is the pulse interval, is the order of the light pulses, The first phase is added in the process of generating the first backward Rayleigh scattered light signal. The second phase is added in the process of generating the second backscattered Rayleigh light signal. represents the imaginary part, for The first amplitude of the first backscattered Rayleigh light at time , for The second amplitude of the second backscattered Rayleigh light at time , is the first frequency, is the second frequency.

[0010] Optionally, 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 Rayleigh backscattered light signal is obtained based on a first light pulse modulated by the first acousto-optic modulator, and the second Rayleigh backscattered light signal is obtained based on a second light pulse 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 AOM.

[0011] Optionally, the phase-sensitive optical time-domain reflectometry fiber optic sensing system further includes a laser configured to output light pulses; Local oscillator optical signal The third formula is as follows; The third formula is: ; in, is the amplitude of the local oscillation light, is the initial phase of the local oscillator light, yes The frequency noise value of the laser at this moment.

[0012] Optionally, the phase-sensitive optical time-domain reflectometry fiber optic sensing system further includes a 3dB coupler, the phase demodulation system further includes a photoelectric balance detector and a digital acquisition card, the 3dB coupler includes a first output port and a second output port; obtaining a first discrete signal corresponding to the first beat frequency signal and a second discrete signal corresponding to the second beat frequency signal includes: Determining a first light intensity output from the first output port and a second light intensity output from the second output port based on the 3dB coupler, the local oscillator light signal, the first backscattered Rayleigh light signal, and the second backscattered Rayleigh light signal; Based on the photoelectric balance detector, the total voltage signal corresponding to the first beat frequency signal and the second beat frequency signal is determined; the first beat frequency signal is obtained by extracting the AC signal with the first center frequency from the first light intensity and the second light intensity, and the second beat frequency signal is obtained by extracting the AC signal with the second center frequency from the first light intensity and the second light intensity; the first center frequency is , the second center frequency is ; Based on the digital acquisition card, the total discrete signal corresponding to the total voltage signal is collected; Based on the total discrete signal, a first discrete signal and a second discrete signal are determined.

[0013] 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; and determining the first discrete signal and the second discrete signal based on the total discrete signal includes: Based on the bandpass filtering technology, the first center frequency and the second center frequency, respectively extracting the first initial voltage signal and the second initial voltage signal from the total discrete signal; Based on the mixing technology, the low-pass filtering technology, the first initial voltage signal and the second initial voltage signal, the first voltage sub-signal, the second voltage sub-signal, the third voltage sub-signal and the fourth voltage sub-signal are determined; 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 a combination of the first initial voltage signal and the second discrete signal. The second voltage sub-signal is obtained by mixing and low-pass filtering; the second voltage sub-signal is obtained by mixing the first initial voltage signal and The third voltage sub-signal is obtained by mixing and low-pass filtering; The fourth voltage sub-signal is obtained by mixing and low-pass filtering; Obtained after mixing and low-pass filtering.

[0014] Optionally, determining the first parameter and the second parameter based on the phase demodulation algorithm, the first discrete signal, and the second discrete signal includes: Normalizing 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: ; in, , is the speed of light, The light frequency is The refractive index of light in the sensing fiber, is the first time interval.

[0015] Optionally, 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, the phase differential is calculated 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: .

[0016] Optionally, 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, the tangent parameter is calculated according to the following seventh formula: ; According to the eighth formula below, the differential phase of the phase-sensitive optical time domain reflectometry fiber optic sensing system is calculated: ; The seventh formula is: ; The eighth formula is: ; in, is a third parameter, and the third parameter is determined by an unwinding algorithm. In some embodiments, a phase demodulation system is provided, comprising: a phase-sensitive optical time-domain reflectometry fiber optic sensing system and a data processing module; the phase-sensitive optical time-domain reflectometry fiber optic sensing system is configured to output a first backscattered Rayleigh light signal and a second backscattered Rayleigh light signal generated by the same optical pulse, wherein the first backscattered Rayleigh light signal is generated at a first time, the second backscattered Rayleigh light signal is generated at a second time, and a first time interval exists between the first time and the second time; 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 the first beat signal and a second discrete signal corresponding to the second beat signal; the first beat signal is generated by interference between the first backscattered Rayleigh light signal and the local oscillator light signal, and the second beat signal is generated by interference between the second backscattered Rayleigh light signal and the local oscillator light signal; determining a first parameter and a second parameter based on the phase demodulation algorithm, the first discrete signal, and the second discrete signal; and calculating a differential phase of the phase-sensitive optical time-domain reflectometry fiber optic sensing system based on the first parameter and the second parameter.

[0017] It can be understood that the beneficial effects that can be achieved by the technical solution provided by the phase demodulation system provided above can be referred to the beneficial effects in the phase demodulation method and any of its optional implementations, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0019] Figure 1 A structural block diagram of a phase demodulation system provided in an embodiment of the present application; Figure 2 A structural diagram of a phase demodulation system provided in an embodiment of the present application; Figure 3 A timing diagram of the first light pulse and the second light pulse provided in an embodiment of the present application; Figure 4 This is a flowchart of the phase demodulation method provided in an embodiment of the present application.

[0020] Reference numerals: 100. Phase-sensitive optical time-domain reflectometry fiber-optic sensing system; 101. Narrow-linewidth laser; 102. First fiber coupler; 103. First acousto-optic modulator; 104. Second fiber coupler; 105. Filter; 106. Second acousto-optic modulator; 107. Delay fiber; 108. First optical amplifier; 109. Second optical amplifier; 110. Fiber circulator; 1101. First port; 1102. Second port; 1103. Third port; 111. Sensing fiber; 112. Third optical amplifier; 113. Third fiber coupler; 114. Photoelectric balanced detector; 115. Digital acquisition card; 200. Data processing module; 201. Computer; 202. Mobile phone. DETAILED DESCRIPTION

[0021] The following will clearly describe the technical solutions in the embodiments of the present application 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, not all of the embodiments. Based on the embodiments of the present application, other embodiments obtained by ordinary technicians in this field without making any creative work are all within the scope of protection of this application.

[0022] Hereinafter, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified with "first," "second," etc., may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0023] In addition, in this application, directional terms such as "upper", "lower", "inner" and "outer" are defined relative to the orientation of the components in the drawings. It should be understood that these directional terms are relative concepts. They are used for relative description and clarification, and they can change accordingly according to changes in the orientation of the components in the drawings.

[0024] To facilitate understanding of the technical solution of the application, the relevant technologies involved in this application are first explained below.

[0025] The phase-sensitive optical time-domain reflectometry fiber optic sensing system is capable of distributed multi-point real-time monitoring of tiny signals over long distances. It has the characteristics of high sensitivity, large spatial dynamic range, and high positioning accuracy. Therefore, it has broad market application prospects in health monitoring of large facilities, industrial production process detection, perimeter security, pipeline protection, marine engineering, etc.

[0026] Currently, phase demodulation of interferometric fiber optic sensing systems (including phase-sensitive optical time-domain reflectometry fiber optic sensing systems) is mainly based on hardware phase demodulation solutions including phase-generated carriers, phase demodulation based on 3×3 coupler structures, and I / Q demodulation.

[0027] Phase-Generated Carrier (PGC) is a common phase demodulation method used in interferometric fiber-optic sensing systems. PGC modulates the phase of light by applying a high-frequency carrier wave to the interferometric signal, allowing phase information, which is difficult to demodulate directly, to be extracted through spectrum conversion. Because PGC requires a phase modulator and demodulator, it increases system complexity and cost. Furthermore, PGC relies on precise phase modulation, and any modulation error will affect the final demodulation accuracy.

[0028] The phase demodulation method based on a 3×3 coupler structure is a widely used phase demodulation technique in fiber interferometers. By utilizing the unique structure of the 3×3 fiber coupler, it can split the fiber interference signal into three paths and achieve phase demodulation through mathematical calculations. This method is commonly used in systems such as fiber optic gyroscopes (FOGs) and offers high demodulation accuracy and stability. However, the demodulation accuracy of the phase demodulation method based on the 3×3 coupler structure is limited by coupler manufacturing errors, which can lead to inaccurate phase demodulation. Due to the use of multiple couplers and other optical components, the system suffers from significant losses, which can weaken the optical signal and affect the demodulation effect.

[0029] I / Q demodulation (In-phase and Quadrature Demodulation) is a common method for extracting useful information from modulated signals. It is widely used in communications systems, radar, software-defined radio, fiber-optic sensors, and other fields. However, I / Q demodulation requires complex circuit design, including quadrature modulators, photoelectrically balanced detectors, and high-performance signal processing circuits. This increases system complexity and cost, often requiring real-time processing of large amounts of data, placing high demands on the system's computing power and processing speed. It is also very sensitive to phase noise in the system, particularly light source phase noise and phase jitter within the system, which can lead to demodulation errors.

[0030] Therefore, the existing phase demodulation methods have problems such as high cost, complex system, high noise, and large computational complexity, which seriously affect the practical application and industrialization of phase-sensitive optical time-domain reflectometry fiber optic sensing systems.

[0031] In addition, the conventional Φ-OTDR system needs to record the two positions and , in order to demodulate the digital difference, the data storage requirements of the hardware demodulation system are relatively high. The phase demodulation method provided in the embodiment of the present application can obtain the phase difference at two different positions at the same time by generating the light pulse a and light pulse b from the same light pulse. , the phase difference can be directly obtained by differential .

[0032] Figure 1 This is a structural block diagram of the phase demodulation system provided in an embodiment of the present application.

[0033] To address the above technical issues, embodiments of the present application provide a phase demodulation system, comprising: 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 backscattered Rayleigh light signal and a second backscattered Rayleigh light signal generated by the same optical pulse, wherein the first backscattered Rayleigh light signal is generated at a first time, the second backscattered Rayleigh light signal is generated at a second time, and a first time interval exists 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 signal and a second discrete signal corresponding to the second beat signal; the first beat signal is generated by interference between the first backward Rayleigh scattered light signal and the local oscillator light signal, and the second beat signal is generated by interference between the second backward Rayleigh scattered light signal and the local oscillator light signal; based on the first beat signal and the second beat signal, the differential phase of the phase-sensitive optical time domain reflectometry fiber optic sensing system 100 is demodulated.

[0034] Figure 2 This is a structural diagram of the phase demodulation system provided in an embodiment of the present application.

[0035] Optionally, the phase-sensitive optical time-domain reflection fiber optic sensing system 100 includes: a narrow linewidth laser 101, a first fiber coupler 102, a first acousto-optic modulator 103, a second 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, a fiber circulator 110, a sensing fiber 111, a third optical amplifier 112, a third 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 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 a first optical frequency. The optical pulse a of the second fiber coupler 104 has a splitting ratio of 50:50. The filter 105 is configured to eliminate noise in the optical pulse a. The second acousto-optic modulator 106 is configured to modulate the optical pulse a to have a second optical frequency The delay fiber 107 is configured to adjust the first time interval between the light pulse a and the light pulse b. . The first optical amplifier 108 is configured to amplify the energy of light pulse b to be the same as the energy of light pulse a. The second optical amplifier 109 is configured to amplify the energy of light pulse a and light pulse b. The optical fiber circulator 110 includes a first port 1101, a second port 1102 and a third port 1103. The sensing optical fiber 111 is configured to input light pulse a to generate a first backward Rayleigh scattered light signal, and input light pulse b to generate a second backward Rayleigh scattered light signal. The third optical amplifier 112 is configured to amplify the energy of the first backward Rayleigh scattered light signal and the second backward Rayleigh scattered light 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 collect the total voltage signal output by the photoelectric balanced detector 114 as a total discrete signal.

[0036] Figure 3 This is a timing diagram of the first light pulse and the second light pulse provided in an embodiment of the present application.

[0037] Specifically, the narrow linewidth laser 101 outputs the initial laser d (with an optical frequency of The initial laser d is divided into two parts by the first fiber coupler 102. One part is the local oscillation light (local oscillation light signal c), and the remaining part is modulated into the first optical pulse (i.e., optical pulse a, with an optical frequency of , pulse width w, and optical pulse repetition frequency f). Light pulse a passes through the second optical fiber coupler 104, and 50% of light pulse a enters the second optical amplifier 109. The remaining 50% of light pulse a passes through the filter 105 and the second acousto-optic modulator 106 in sequence and is modulated into a second light pulse (i.e., light pulse b, with an optical frequency of , pulse width is w, and optical pulse repetition frequency is f). Light pulse b passes through delay fiber 107, so that there is a first time interval between light pulse b and light pulse a (the timing diagram of light pulse a and light pulse b is shown in FIG. Figure 3As shown). Light pulse b then enters the first optical amplifier 108, which amplifies the energy of light pulse b to be equal to that of light pulse a. After light pulse b enters the second fiber coupler 104, 50% of light pulse b enters the second optical amplifier 109 after light pulse a. After both light pulse a and light pulse b are amplified to the required energy, they enter the fiber circulator 110 through the first port 1101 of the fiber circulator 110 and are then output through the second port 1102 of the fiber circulator 110 and transmitted to the sensing fiber 111, generating a first backward Rayleigh scattered light signal. (corresponding to light pulse a) and the second backscattered Rayleigh light signal After passing through the optical pulse b, it enters the optical fiber circulator 110 through its second port 1102 and is then transmitted to the third optical amplifier 112 via its third port 1103 for further amplification, thereby increasing the power of the first and second backscattered Rayleigh light signals. The backscattered Rayleigh signals (first and second backscattered Rayleigh light signals) and the local oscillator (LO) light signal undergo beat frequency interference through the third fiber coupler 113. The two beat frequency interference signals (first and second beat frequency signals) output by the third fiber coupler 113 are converted into electrical signals (first and second voltage signals) by the photoelectric balanced detector 114. The digital acquisition card 115 acquires the electrical signals to generate discrete signals (first and second discrete signals). The data processing module 200 then performs phase demodulation to obtain the differential phase of the phase-sensitive optical time-domain reflectometry fiber optic sensing system 100.

[0038] For example, in combination Figure 3 As shown, light pulse a1 and light pulse b1 are generated by the same light pulse d1, light pulse a2 and light pulse b2 are generated by the same light pulse d2, there is a first time interval δt between the starting time 0 of light pulse a1 and the starting time δt of light pulse b1, there is a first time interval δt between the ending time w of light pulse a1 and the ending time δt+w of light pulse b1, there is a first time interval δt between the starting time T of light pulse a2 and the starting time T+δt of light pulse b2, and there is a first time interval δt between the ending time T+w of light pulse a2 and the ending time T+δt+w of light pulse b2.

[0039] Specifically, the third fiber coupler 113 is a 3dB coupler, which 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 scattered light signal and a second backward Rayleigh scattered light signal, the second input port is configured to input a local oscillator light signal, the first output port is configured to output a first light intensity, and the second output port is configured to output a second light intensity. The photoelectric balanced detector 114 is configured to receive the first light intensity and the second light intensity output by the 3dB coupler, and is also configured to 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 the 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 the second center frequency from the first light intensity and the second light intensity; the first center frequency is , the second center frequency is The digital acquisition card 115 is in communication with the photoelectric balance detector 114 ; the digital acquisition card 115 is configured to acquire the total voltage signal and also configured to acquire the total discrete signal corresponding to the total voltage signal.

[0040] 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.

[0041] Alternatively, as Figure 2 As 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). It is sufficient that the data processing module 200 can realize the above functions.

[0042] Figure 4 This is a flowchart of the phase demodulation method provided in an embodiment of the present application.

[0043] Combine Figure 1 and Figure 2 The phase demodulation system shown in the embodiment of the present application also provides a phase demodulation method, which is applied to the phase demodulation system, such as Figure 4 As shown, the phase demodulation method includes steps S100 to S300, which are specifically as follows:

[0044] Step S100, obtaining a first discrete signal corresponding to the first beat signal and a second discrete signal corresponding to the second beat signal; the first beat signal is generated by interference between the first backward Rayleigh scattered light signal and the local oscillator light signal, and the second beat signal is generated by interference between the second backward Rayleigh scattered light signal and the local oscillator light signal.

[0045] Specifically, combined Figure 2As shown, the first backward Rayleigh scattering optical signal generated by the optical pulse a passing through the sensing optical fiber 111 and the formula between the time t is as shown in the following (1). The second backward Rayleigh scattering optical signal generated by the optical pulse b passing through the sensing optical fiber 111 and the formula between the time t is as shown in the following (2).

[0046] (1).

[0047] (2).

[0048] 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 is the refractive index of light in the sensing optical fiber.

[0049] Specifically, the time corresponding to t = 0 is the time when the optical pulse enters the sensing optical fiber.

[0050] .

[0051] , is the central angular frequency of the laser 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.

[0052] It can be seen from the above (1) that at a certain time 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 the time corresponds to the information of the detection optical fiber position . Among them, 0 ≤ < T, and T is the pulse interval.

[0053] Assuming that the light repetition frequency (i.e., the repetition frequency of the light pulse) is f, T = 1 / f, the backscattered Rayleigh light signals generated by the Nth light pulse a and light pulse b through the sensing fiber are as follows (3) and (4), respectively: (3).

[0054] (4).

[0055] Optionally, the first backscattered Rayleigh light signal The first formula is as follows; The first formula is: ; The second backscattered Rayleigh light signal The second formula is as follows; The second formula is: ; in, is the pulse interval, is the order of the light pulses, The first phase is added in the process of generating the first backward Rayleigh scattered light signal. The second phase is added in the process of generating the second backscattered Rayleigh light signal. represents the imaginary part, for The first amplitude of the first backscattered Rayleigh light at time , for The second amplitude of the second backscattered Rayleigh light at time , is the first frequency, is the second frequency.

[0056] In this embodiment, the first Rayleigh backscattered light signal and the second Rayleigh backscattered light signal are represented by complex amplitudes to facilitate subsequent phase demodulation.

[0057] Specifically, for ease of understanding, the first formula is referred to as (5) and the second formula is referred to as (6) to continue the above description.

[0058] Optionally, combined 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 Rayleigh backscattered light signal is obtained based on a first light pulse (light pulse a) modulated by the first acousto-optic modulator 103, and the second Rayleigh backscattered light signal is obtained based on a second light pulse (light pulse b) modulated by the first and second acousto-optic modulators. , 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 AOM.

[0059] In this embodiment, the first optical pulse is obtained by modulating the initial laser light based on the first acousto-optic modulator 103, and a portion of the first optical pulse is modulated by the second acousto-optic modulator 106 to obtain a second optical pulse. Then, the remaining portion of the first optical pulse passes through the sensing fiber 111 to obtain a first backscattered Rayleigh light signal, and the second optical pulse passes through the sensing fiber 111 to obtain a second backscattered Rayleigh light signal. including the frequency shift center of the first acousto-optic modulator, It includes the frequency shift center of the first acousto-optic modulator and the frequency shift center of the second acousto-optic modulator.

[0060] Specifically, the Φ-OTDR system is a coherent detection system that requires a laser source with both stable frequency output and excellent monochromaticity. However, frequency drift introduced by the laser can severely degrade the sensing performance of the Φ-OTDR system, causing the demodulated phase to drift, compromising the integrity of the measured signal, causing waveform distortion, and reducing the system's signal-to-noise ratio, leading to inaccurate information such as the location and frequency of disturbance events. Laser frequency drift is a slow-varying signal with a low frequency of change, which can severely interfere with the system's ability to monitor low-frequency signals.

[0061] To suppress the effects of laser frequency drift and frequency noise on the system, related technologies have proposed using an auxiliary interferometer to measure the laser's frequency drift and compensate for frequency drift in the sensing path. However, this increases system complexity, and the use and configuration of the reference interferometer significantly impacts the suppression effect. Alternatively, related technologies use a quadratic difference method to compensate for frequency drift. However, this requires searching for a compensation signal in an interference-free area near the disturbance zone, and the selection of the compensation signal significantly impacts the compensation effect.

[0062] Therefore, the phase demodulation method provided in the embodiment of the present application, through the mixing technology in the phase demodulation algorithm, obtains 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, 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) obtained after mixing the first initial voltage signal and the second initial voltage signal in the total output voltage, thereby being able to directly eliminate the frequency noise value of the laser, and then being able to directly demodulate the differential phase that is not affected by the laser noise, thereby improving the accuracy of the differential phase obtained by demodulation and improving the system's monitoring capability of low-frequency signals.

[0063] Optionally, the phase-sensitive optical time-domain reflectometry fiber optic sensing system further includes a laser configured to output light pulses; Local oscillator optical signal The third formula is as follows; The third formula is: ; in, is the amplitude of the local oscillation light, is the initial phase of the local oscillator light, yes The frequency noise value of the laser at this moment.

[0064] Specifically, for ease of understanding, the third formula is taken as (7) to continue the above description.

[0065] For example, a laser such as Figure 2 As shown in the narrow linewidth laser 101 shown in FIG.

[0066] Specifically, as can be seen from the third formula above, the local oscillator light signal contains The frequency noise value of the laser at the moment, that is, the frequency noise caused by the frequency drift caused by the laser.

[0067] Optionally, combined Figure 2 As shown, the phase-sensitive optical time-domain reflectometry fiber optic sensing system 100 further includes a 3dB coupler (third fiber coupler 113), and the phase demodulation system further includes a photoelectrically balanced detector 114 and a digital acquisition card 115. The 3dB coupler includes a first output port and a second output port. Step S100 includes steps S101 to S104, which are specifically as follows: Step S101 : determining a first light intensity output from a first output port and a second light intensity output from a second output port based on a 3dB coupler, a local oscillator light signal, a first backscattered Rayleigh light signal, and a second backscattered Rayleigh light signal.

[0068] Optionally, the first light intensity As follows (8): (8); in, As shown below (9), As shown below (10).

[0069] (9); (10).

[0070] Second light intensity As follows (11): (11); in, As shown below (12), As shown below (13).

[0071] (12); (13).

[0072] in, for The first amplitude of the first backscattered Rayleigh light at time , yes The frequency noise value of the laser at this moment, yes The phase of the moment.

[0073] Specifically, 、 、 and The deduction process is as follows: (9).

[0074] (10).

[0075] (12).

[0076] (13).

[0077] Specifically, in (9), (10), (12) and (13) above represents conjugation, e.g. for The conjugate of . Combined with the above 、 、 and There are three items, the first two items represent the DC part of the light intensity, and the third item is the AC part of the light intensity, that is, the beat frequency signal. Therefore, the center frequency of the first light intensity and the second light intensity is extracted as The first beat frequency signal is obtained by the AC signal, and the center frequency of the first light intensity and the second light intensity is extracted as The AC signal is used to obtain a second beat frequency signal.

[0078] Step S102: Determine the total voltage signal corresponding to the first beat frequency signal and the second beat frequency signal based on the photoelectric balance detector; the first beat frequency signal is obtained by extracting the AC signal with the first center frequency from the first light intensity and the second light intensity, and the second beat frequency signal is obtained by extracting the AC signal with the second center frequency from the first light intensity and the second light intensity. The first center frequency is , the second center frequency is .

[0079] Optionally, the first beat frequency signal As follows (14): (14); The second beat frequency signal As follows (15): (15); in, for The first amplitude of the first backscattered Rayleigh light at time , yes The phase of the moment.

[0080] Step S103: collecting the total discrete signal corresponding to the total voltage signal based on the digital acquisition card.

[0081] Step S104: determining a first discrete signal and a second discrete signal based on the total discrete signal.

[0082] 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: Step S1041 : extracting a first initial voltage signal and a second initial voltage signal from the total discrete signal based on a bandpass filtering technique, a first center frequency, and a second center frequency.

[0083] Specifically, the total discrete signal As shown below (16): (16).

[0084] in, is the first initial voltage signal, is the second initial voltage signal.

[0085] Specifically, the first initial voltage signal As shown below (17): (17).

[0086] The second initial voltage signal As shown below (18): (18).

[0087] Step S1042: Based on the frequency mixing technology, the 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 a combination of the first initial voltage signal and the second discrete signal. The second voltage sub-signal is obtained by mixing and low-pass filtering; the second voltage sub-signal is obtained by mixing the first initial voltage signal and The third voltage sub-signal is obtained by mixing and low-pass filtering; The fourth voltage sub-signal is obtained by mixing and low-pass filtering; Obtained after mixing and low-pass filtering.

[0088] In this embodiment, the first and second initial voltage signals are extracted from the total discrete signal based on the first and second center frequencies, thereby facilitating mixing and low-pass filtering the first initial voltage signal to obtain the first and second voltage sub-signals, and mixing and low-pass filtering the second initial voltage signal to obtain the third and fourth voltage sub-signals. This facilitates eliminating the frequency noise value of the laser based on the first, second, third, and fourth voltage sub-signals, thereby enabling direct demodulation of a differential phase unaffected by laser noise, improving the accuracy of the demodulated differential phase, and enhancing the system's ability to monitor low-frequency signals.

[0089] Specifically, the first voltage sub-signal As shown below (19): (19).

[0090] The second voltage sub-signal As shown below (20): (20).

[0091] The third voltage sub-signal As shown below (21): (twenty one).

[0092] Fourth voltage sub-signal As shown below (22): (twenty two).

[0093] In this embodiment, the first discrete signal and the second discrete signal are determined to demodulate the differential phase of the phase-sensitive optical time domain reflectometry fiber optic sensing system according to the first discrete signal and the second discrete signal.

[0094] Specifically, corresponding to position , corresponding to position . According to the time 0 ≤ <T and the relationship with the detection position , collect the first discrete signal (as shown in (23) and (24) below) and the second discrete signal (as shown in (25) and (26) below). The first discrete signal includes the first voltage sub-signal ( , as shown in (23) below) and the second voltage sub-signal ( , as shown in (24) below), and the second discrete signal includes the third voltage sub-signal ( , as shown in (25) below) and the fourth voltage sub-signal ( , as shown in (26) below).

[0095] (23).

[0096] (24).

[0097] (25).

[0098] (26).

[0099] Wherein, , is the first time interval.

[0100] 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.

[0101] Optionally, step S200 includes step S201 and step S202, specifically as follows: Step S201, normalize the first voltage sub-signal, the second voltage sub-signal, the third voltage sub-signal and the fourth voltage sub-signal, and 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.

[0102] Specifically, step S201 includes S2011 to step S2014, specifically as follows: Step S2011, based on the first voltage sub-signal and the second voltage sub-signal , calculate the first normalization parameter .

[0103] Specifically, calculate the first normalization parameter As shown below (27): (27).

[0104] Step S2012: Use the first normalization parameter to convert the amplitudes of the first voltage sub-signal and the second voltage sub-signal to 1. That is, the first voltage sub-signal is divided by the first normalization parameter, and the second voltage sub-signal is divided by the first normalization parameter.

[0105] Specifically, the normalized first voltage sub-signal (i.e., the first normalized signal ) is shown below (28): (28).

[0106] The normalized second voltage sub-signal (i.e., the second normalized signal ) is shown below (29): (29).

[0107] Step S2013: Based on the third voltage sub-signal and the fourth voltage sub-signal , calculate the second normalization parameter .

[0108] Specifically, the second normalization parameter is calculated As shown below (30): (30).

[0109] Step S2014: Use the second normalization parameter to convert the amplitudes of the third and fourth voltage sub-signals to 1. That is, the third voltage sub-signal is divided by the second normalization parameter, and the fourth voltage sub-signal is divided by the second normalization parameter.

[0110] Specifically, the normalized third voltage sub-signal (ie, the third normalized signal ) is shown below (31): (31).

[0111] The fourth normalized voltage sub-signal (ie, the fourth normalized signal ) is shown below (32): (32).

[0112] 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, thereby eliminating the influence of the amplitude in the calculation.

[0113] Step S202: 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: ; in, , is the speed of light, The light frequency is The refractive index of light in the sensing fiber, is the first time interval.

[0114] Specifically, for ease of understanding, the fourth formula is expressed as (33) and the fifth formula is expressed as (34) to continue the above description.

[0115] Step S300 : 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.

[0116] Optionally, step S300 includes step S301 and step S302, which are specifically as follows: Step S301: Based on the first parameter and the second parameter, calculate the phase differential according to the following sixth formula: .

[0117] Step S302: 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: .

[0118] Specifically, for ease of understanding, the sixth formula is taken as (35) to continue the above description.

[0119] Optionally, step S300 includes step S303 and step S304, which are specifically as follows: Step S303: Based on the first parameter and the second parameter, the tangent parameter is calculated according to the following seventh formula: .

[0120] The seventh formula is: .

[0121] Step S304: Calculate the differential phase of the phase-sensitive optical time domain reflectometry fiber optic sensing system according to the eighth formula below: .

[0122] The eighth formula is: .

[0123] Wherein, m is the third parameter, and the value of m is determined by the unwinding algorithm.

[0124] Specifically, for ease of understanding, the seventh formula is expressed as (36) and the eighth formula is expressed as (37) to continue the above description.

[0125] The phase demodulation method provided in the embodiments of the present application uses a first discrete signal and a second discrete signal outputted by a phase-sensitive optical time-domain reflectometry fiber-optic sensor system at a first time interval to directly demodulate the differential phase between two different locations in the system. This reduces the system's storage capacity requirements and improves the demodulation efficiency of the differential phase. Furthermore, during the demodulation process, the frequency noise introduced by the laser can be directly eliminated, thereby improving the system's signal-to-noise ratio.

[0126] Specifically, the conventional Φ-OTDR system needs to record the two positions, and, , in order to demodulate the digital difference, the data storage requirements of the hardware demodulation system are relatively high. The phase demodulation method provided in the embodiment of the present application can simultaneously obtain the phase and , can be directly differentiated to obtain phase difference, .

[0127] Specifically, the phase demodulation method provided in the embodiment of the present application includes the above (1) to (35), or (1) to (34), (36), and (37).

[0128] Corresponding to the aforementioned embodiment of the phase demodulation method, the present application also provides an embodiment of a phase demodulation system. The phase demodulation system includes: a phase-sensitive optical time-domain reflection fiber optic sensing system and a data processing module; the phase-sensitive optical time-domain reflection fiber optic sensing system is configured to output a first backward Rayleigh scattered light signal and a second backward Rayleigh scattered light signal generated by the same optical pulse, the first backward Rayleigh scattered light signal is generated at a first time, the second backward Rayleigh scattered light signal is generated at 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 optical time-domain reflection fiber optic 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 interference between the first backward Rayleigh scattered light signal and the local oscillator light signal, and the second beat frequency signal is generated by interference between the second backward Rayleigh scattered light signal and the local oscillator light 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, a differential phase of the phase-sensitive optical time-domain reflection fiber optic sensing system is calculated.

[0129] The phase demodulation system provided in the embodiments of the present application uses a first discrete signal and a second discrete signal outputted by a phase-sensitive optical time-domain reflectometry fiber-optic sensor system at a first time interval to directly demodulate the differential phase between two different locations in the system. This reduces the system's storage capacity requirements and improves the demodulation efficiency of the differential phase. Furthermore, during the demodulation process, the frequency noise generated by the laser can be directly eliminated, thereby improving the system's signal-to-noise ratio.

[0130] It should be noted that those skilled in the art will readily conceive of other embodiments of the present application after considering the specification and practicing the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered merely as exemplary, and the true scope of this application is indicated by the claims.

[0131] It should be understood that the present application is not limited to the exact structures described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A phase demodulation method, characterized in that: The phase demodulation method is applied to a phase demodulation system, the phase demodulation system includes a phase-sensitive optical time domain reflection optical fiber sensing system, the phase-sensitive optical time domain reflection optical fiber sensing system outputs a first backward Rayleigh scattered light signal and a second backward Rayleigh scattered light signal generated by the same optical pulse, the generation time of the first backward Rayleigh scattered light signal is a first time, the generation time of the second backward Rayleigh scattered light signal is a second time, and there is a first time interval between the first time and the second time; the phase demodulation method includes: Acquire a first discrete signal corresponding to a first beat frequency signal and a second discrete signal corresponding to a second beat frequency signal; wherein the first beat frequency signal is generated by interference between the first backward Rayleigh scattered light signal and a local oscillator light signal, and the second beat frequency signal is generated by interference between the second backward Rayleigh scattered light signal and the local oscillator light signal; Determining a first parameter and a second parameter based on a phase demodulation algorithm, the first discrete signal, and the second discrete signal; Based on the first parameter and the second parameter, a differential phase of the phase-sensitive optical time-domain reflectometry fiber optic sensing system is calculated.

2. The phase demodulation method according to claim 1, characterized in that: The first backscattered Rayleigh light signal The first formula is as follows; The first formula is: ； The second backscattered Rayleigh light signal The second formula is as follows; The second formula is: ； in, is the pulse interval, is the order of the light pulses, A first phase is added during the process of generating the first backscattered Rayleigh light signal, A second phase is added during the process of generating the second backscattered Rayleigh light signal, represents the imaginary part, for The first amplitude of the first back-Rayleigh scattered light at time instant, for The second amplitude of the second backscattered Rayleigh light at time instant, is the first frequency, is the second frequency.

3. The phase demodulation method according to claim 2, characterized in that: The phase-sensitive optical time-domain reflectometry fiber-optic sensing system comprises a first acousto-optic modulator and a second acousto-optic modulator; The first backscattered Rayleigh light signal is obtained based on a first light pulse modulated by the first AOM, and the second backscattered Rayleigh light signal is obtained based on a second light pulse modulated by the first AOM and the second AOM; , 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 AOM.

4. The phase demodulation method according to claim 1, characterized in that: The phase-sensitive optical time-domain reflectometry fiber-optic sensing system further includes a laser, which is configured to output the optical pulse; The local oscillator optical signal The third formula is as follows; The third formula is: ； Among them, the is the amplitude of the local oscillation light, is the initial phase of the local oscillator light, yes The frequency noise value of the laser at the time.

5. The phase demodulation method according to claim 4, characterized in that: The phase-sensitive optical time-domain reflectometry fiber optic sensing system further comprises a 3dB coupler, the phase demodulation system further comprises a photoelectric balance detector and a digital acquisition card, and the 3dB coupler comprises a first output port and a second output port; Acquiring a first discrete signal corresponding to the first beat frequency signal and a second discrete signal corresponding to the second beat frequency signal, including: Determine a first light intensity output from the first output port and a second light intensity output from the second output port based on the 3dB coupler, the local oscillator light signal, the first backscattered Rayleigh light signal, and the second backscattered Rayleigh light signal; Based on the photoelectric balance detector, a total voltage signal corresponding to the first beat frequency signal and the second beat frequency signal is determined; the first beat frequency signal is obtained by extracting an AC signal whose center frequency is 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 whose center frequency is a second center frequency from the first light intensity and the second light intensity; the first center frequency is , the second center frequency is ; Based on the digital acquisition card, a total discrete signal corresponding to the total voltage signal is acquired; Based on the total discrete signal, the first discrete signal and the second discrete signal are determined.

6. The phase demodulation method according to claim 5, characterized in that: 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 the first discrete signal and the second discrete signal based on the total discrete signal comprises: Based on the bandpass filtering technology, the first center frequency and the second center frequency, respectively extracting the first initial voltage signal and the second initial voltage signal from the total discrete signal; Based on the mixing technology, the low-pass filtering technology, the first initial voltage signal and the second initial voltage signal, a first voltage sub-signal, a second voltage sub-signal, a third voltage sub-signal and a fourth voltage sub-signal are determined; the first discrete signal includes the first voltage sub-signal and the second voltage sub-signal, the second discrete signal includes the third voltage sub-signal and the fourth voltage sub-signal; the first voltage sub-signal is a combination of the first initial voltage signal and the The second voltage sub-signal is obtained by mixing and low-pass filtering; the second voltage sub-signal is obtained by mixing the first initial voltage signal and The third voltage sub-signal is obtained by mixing and low-pass filtering; the third voltage sub-signal is obtained by mixing the second initial voltage signal and The fourth voltage sub-signal is obtained by mixing and low-pass filtering; the fourth voltage sub-signal is obtained by mixing the second initial voltage signal and Obtained after mixing and low-pass filtering.

7. The phase demodulation method according to claim 6, characterized in that: 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 comprises: Normalizing 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 fourth formula as follows , calculate the second parameter according to the fifth formula as follows ; The fourth formula is: ； The fifth formula is: ； Among them, the , is the speed of light, The light frequency is The refractive index of light in the sensing fiber is is the first time interval.

8. The phase demodulation method according to claim 7, characterized in that: The 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, the phase differential is calculated 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: 。 9. The phase demodulation method according to claim 7, characterized in that: The 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, the tangent parameter is calculated according to the seventh formula as follows: ; According to the eighth formula below, the differential phase of the phase-sensitive optical time domain reflectometry fiber optic sensing system is calculated: ; The seventh formula is: ； The eighth formula is: ； Among them, the is a third parameter, and the third parameter is determined by an unwrapping algorithm.

10. A phase demodulation system, characterized in that: include: Phase-sensitive optical time-domain reflectometry fiber optic sensing system and data processing module; The phase-sensitive optical time-domain reflectometry fiber optic sensing system is configured to output a first backscattered Rayleigh light signal and a second backscattered Rayleigh light signal generated by a same optical pulse, wherein the first backscattered Rayleigh light signal is generated at a first time, the second backscattered Rayleigh light signal is generated at 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 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 scattered light signal and a local oscillator light signal, and the second beat frequency signal is generated by interference between the second backward Rayleigh scattered light signal and the local oscillator light signal; Based on the 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, a differential phase of the phase-sensitive optical time-domain reflectometry fiber optic sensing system is calculated.

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