A method and apparatus for phase demodulation of a fiber optic DAS

Abstract

This invention provides a fiber optic DAS phase demodulation method and demodulation device. The demodulation method includes: S1, acquiring the digital signal of the sensing fiber under each pulse signal; S2, performing sub-band extraction and matched filtering on the digital signal under each pulse signal and the digital signal under pulse signals at a preset interval, followed by adjacent differential rotating vector summation to obtain a complex signal; S3, solving for the phase angle of each complex signal and expanding the phase angle to obtain a phase signal; S4, performing spatial differential processing on each phase signal to obtain a phase demodulated signal; S5, extracting the sampling points corresponding to the fiber sampling positions in each phase demodulated signal according to preset fiber sampling positions to obtain a vibration signal; and sequentially performing windowing processing, FFT transformation, frequency domain compensation, IFFT transformation, and windowing processing on the vibration signal, and outputting the result. This method can eliminate accumulated errors while preserving the complete frequency response range.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a fiber optic DAS phase demodulation method and demodulation device. Background Technology

[0002] OTDR technology, also known as optical time-domain reflectometry, obtains sensing information along an optical fiber based on the time of flight of light. When demodulation is performed using the phase of the backscattered Rayleigh signal, it becomes a phase-sensitive OTDR, or Φ-OTDR system, also called a DAS system. The DAS system sends probe pulse signals to the sensing fiber at fixed periods. At the receiver of the DAS system, the backscattered Rayleigh light signal at each point along the fiber is received. By demodulating the phase of these signals, the vibration distribution along the fiber can be dynamically demodulated.

[0003] The backscattered Rayleigh light signal received under the pulse signal emitted by the DAS system exhibits relatively strong coherent fading noise. This coherent fading noise is generally eliminated by rotating vector summation. Currently, there are two methods for rotating vector summation: 1. Selecting a reference signal curve, and then subtracting all subsequent acquired signal curves from this reference curve. However, the reference signal curve is affected by the stability of the light source and optical path. Good light source and optical path stability result in good demodulation results; if the reference signal curve selection is flawed, all demodulation results will be problematic, and cumulative errors will exist, making them difficult to eliminate. 2. Subtracting adjacent acquired signal curves, which is equivalent to performing first-order differential processing on the probe signal. Although this can eliminate the influence of cumulative errors, its effect is similar to a high-pass filter, significantly suppressing useful low-frequency signals after signal processing, thus limiting the demodulation frequency response range.

[0004] Therefore, there is an urgent need for an improved fiber optic DAS phase demodulation method and demodulation device. Summary of the Invention

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides an optical fiber DAS phase demodulation method and demodulation device that can eliminate accumulated errors and retain the complete frequency response range.

[0006] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0007] In a first aspect, the present invention provides a fiber optic DAS phase demodulation method, comprising the following steps:

[0008] S1. Acquire the digital signal under each pulse signal emitted by the sensing fiber in the DAS system;

[0009] S2. After sub-band extraction and matched filtering of the digital signal under each pulse signal and the digital signal under the pulse signal at a preset interval, adjacent differential rotating vector summation is performed to obtain a complex signal; wherein, the preset interval is an integer multiple of the pulse signal transmission interval;

[0010] S3. Perform arctan operation on each complex signal to solve for the phase angle, and expand the phase angle to obtain the phase signal of the sensing fiber under each pulse.

[0011] S4. Perform spatial differential processing on each phase signal to obtain the phase demodulation signal of the sensing fiber under each pulse.

[0012] S5. Based on the preset fiber sampling position, extract the sampling points corresponding to the fiber sampling position in each phase demodulation signal, arrange all sampling points according to the sampling time, and obtain the vibration signal of the fiber sampling position; perform windowing processing and FFT transformation on the vibration signal in sequence, then perform low-frequency domain compensation on the vibration signal according to the preset frequency domain compensation coefficient, and then perform IFFT transformation and windowing processing on the frequency domain compensated vibration signal in sequence, and output the result.

[0013] Optionally, the pulse signal transmitted by the DAS system is a single-frequency signal or a swept-frequency signal.

[0014] Optionally, S2 includes: using the pulse intra-frequency division method to divide the digital signal under each pulse into a preset number of signals with different frequency bands, performing first-order differential processing on the different frequency band signals under each pulse signal and the corresponding frequency band signals of the pulse signal at a preset interval to obtain the first-order differential result corresponding to each pulse signal, and adding all the first-order differential results corresponding to each pulse signal to obtain the complex signal of the sensing fiber under each pulse.

[0015] Optionally, in S1, two backscattered Rayleigh light signals are acquired under each pulse signal emitted by the sensing fiber in the DAS system, and the two backscattered Rayleigh light signals are converted into two digital signals.

[0016] Optionally, the digital signal under each pulse is divided into a preset number of signals with different frequency bands using the intra-pulse frequency division method, including:

[0017] The two digital signals acquired by the sensing fiber under each pulse signal transmitted by the DAS system are the X-channel digital signal DATA_X_M and the Y-channel digital signal DATA_Y_M, respectively.

[0018] Copy DATA_X_M to obtain DATA_X_S; copy DATA_Y_M to obtain DATA_Y_S;

[0019] Input DATA_X_M, DATA_X_S, DATA_Y_M, and DATA_Y_S into their respective frequency band division links to obtain different frequency band signals corresponding to DATA_X_M, DATA_X_S, DATA_Y_M, and DATA_Y_S.

[0020] Add the corresponding frequency band signals in DATA_X_M and DATA_X_S, and add the corresponding frequency band signals in DATA_Y_M and DATA_Y_S to output the different frequency band signals of the digital signal under each pulse;

[0021] The frequency band division link includes at least two sub-frequency band links set in parallel, and the frequency domain coefficients of the at least two sub-frequency band links are different from each other; the signal is input to the sub-frequency band link, and the signal is sequentially windowed and FFT transformed. Then, the frequency band of the signal is extracted according to the pre-set sub-frequency band frequency domain coefficients. After that, the extracted signal is sequentially IFFT transformed and windowed, and the result is output.

[0022] Optionally, the preset interval is the pulse signal transmission interval.

[0023] Optionally, the different frequency band signals under each pulse signal are subjected to first-order difference processing with the corresponding frequency band signals of pulse signals at a preset interval to obtain the first-order difference result corresponding to each pulse signal, including:

[0024] Signals of different frequency bands under pulse signals are alternately stored in the first first-in-first-out (FIFO) memory and the second first-in-first-out (FIFO) memory according to the transmission order of the pulse signals.

[0025] The different frequency band signals under the current sub-pulse signal are conjugated and then sent to the first FIFO memory and the complex multiplier. At the same time, the different frequency band signals under the previous pulse signal are read from the second FIFO memory and sent to the complex multiplier. In the complex multiplier, the corresponding frequency band signals of the two pulse signals are multiplied and output to obtain the first-order difference result corresponding to the current sub-pulse signal. Alternatively, the different frequency band signals under the current sub-pulse signal are conjugated and then sent to the second FIFO memory and the complex multiplier. At the same time, the different frequency band signals under the previous pulse signal are read from the first FIFO memory and sent to the complex multiplier. In the complex multiplier, the corresponding frequency band signals of the two pulse signals are multiplied and output to obtain the first-order difference result corresponding to the current sub-pulse signal.

[0026] Optionally, in S4, based on a pre-set spatial differential distance, the difference between two sampling points that are spatially separated in each phase signal is calculated to obtain the phase demodulation signal of the sensing fiber under each pulse.

[0027] Optionally, in S5, a sinusoidal window, rectangular window, Hanning window, or Hamming window can be used to window the vibration signal.

[0028] Secondly, the present invention provides an optical fiber DAS phase demodulation device, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program stored in the memory, it implements the steps of the optical fiber DAS phase demodulation method as described above.

[0029] The beneficial effects of this invention are:

[0030] The fiber optic DAS phase demodulation method and demodulation device provided by this invention use two adjacent pulse detection signals as a reference to perform rotating vector summation, which can eliminate accumulated errors. After rotating vector summation and phase demodulation, a frequency domain filter is introduced into the demodulation result of the sampling position using short-time Fourier transform to recover the suppressed low-frequency signal, thereby realizing wide-bandwidth real-time detection of signals from extremely low frequency to high frequency and improving the accuracy and stability of signal processing. Attached Figure Description

[0031] Figure 1 This is a flowchart illustrating the fiber optic DAS phase demodulation method according to a specific embodiment of the present invention.

[0032] Figure 2 This is a schematic diagram of the process of dividing a digital signal into frequency bands according to a specific embodiment of the present invention, wherein Segk(n) is a window function and G(n) is the frequency domain coefficient of the sub-band;

[0033] Figure 3 This is a schematic diagram illustrating the process of performing first-order difference on a digital signal according to a specific embodiment of the present invention.

[0034] Figure 4 This is a schematic diagram of the phase signal of the sensing optical fiber under three pulses according to a specific embodiment of the present invention.

[0035] Figure 5 To Figure 4 A schematic diagram of spatial differential processing of the phase signal in the sensing fiber to obtain the phase demodulation signal under each pulse is obtained.

[0036] Figure 6 This is a schematic diagram of the process of frequency domain compensation of vibration signal according to a specific embodiment of the present invention, where Segk(n) is a window function and H(n) is a frequency domain compensation coefficient. Detailed Implementation

[0037] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] like Figure 1 As shown, this invention provides a fiber optic DAS phase demodulation method. The fiber optic DAS phase demodulation method includes the following steps:

[0039] S1. Acquire the digital signal of each pulse signal emitted by the sensing fiber in the DAS system.

[0040] The pulse signal transmitted by the DAS system is either a single-frequency signal or a swept-frequency signal.

[0041] As an example, in a DAS system, a fixed-period swept-frequency pulse signal drives an acousto-optic modulator to generate a fixed-period swept-frequency pulse optical signal in the optical path. The backscattered Rayleigh light signal returning through the sensing fiber and circulator is also swept-frequency. The electrical signal obtained by the photodetector is also swept-frequency, and the conversion of the electrical signal into a digital signal by the analog-to-digital converter (ADC) is also swept-frequency. For example, if the length of the received return optical pulse is 100µs, taking a 250Msps ADC as an example, the signal length that needs to be processed in one pulse signal is 25,000 points.

[0042] To improve the accuracy of subsequent signal processing, preferably, in the DAS system, two backscattered Rayleigh light signals are acquired by two photodetectors under each pulse signal emitted by the sensing fiber in the DAS system, and the two backscattered Rayleigh light signals are converted into two digital signals by an ADC, which are denoted as X-channel digital signal DATA_X_M and Y-channel digital signal DATA_Y_M, respectively.

[0043] S2. After extracting the sub-frequency band and performing matched filtering on the digital signal under each pulse signal and the digital signal under the pulse signal at a preset interval, perform adjacent differential rotating vector summation to obtain a complex signal; wherein, the preset interval is an integer multiple of the pulse signal transmission interval.

[0044] Preferably, the digital signal under each pulse is divided into a preset number of signals with different frequency bands using the pulse intra-frequency division method. The signals of different frequency bands under each pulse signal are subjected to first-order differential processing with the corresponding frequency band signals of the pulse signal at a preset distance to obtain the first-order differential result corresponding to each pulse signal. All the first-order differential results corresponding to each pulse signal are added together to obtain the complex signal of the sensing fiber under each pulse.

[0045] More preferably, the digital signal under each pulse is divided into a preset number of signals with different frequency bands using the pulse intra-frequency division method, including:

[0046] Copy DATA_X_M to obtain DATA_X_S; copy DATA_Y_M to obtain DATA_Y_S;

[0047] Input DATA_X_M, DATA_X_S, DATA_Y_M, and DATA_Y_S into their respective frequency band division links to obtain different frequency band signals corresponding to DATA_X_M, DATA_X_S, DATA_Y_M, and DATA_Y_S; add the corresponding frequency band signals from DATA_X_M and DATA_X_S, and add the corresponding frequency band signals from DATA_Y_M and DATA_Y_S to output the different frequency band signals of the two digital signals under each pulse;

[0048] The frequency band division link includes at least two sub-frequency band links set in parallel, and the frequency domain coefficients of the at least two sub-frequency band links are different from each other; for example Figure 2 As shown, the signal is input to the sub-band link, and windowing and FFT transformation are performed on the signal in sequence. Then, the frequency band of the signal is extracted according to the preset sub-band frequency domain coefficients. After that, IFFT transformation and windowing are performed on the extracted signal in sequence, and the result is output.

[0049] The frequency band division of pulse signals using the methods described above mostly involves multiplication and addition operations, requiring relatively small computational resources. This makes it suitable for deployment on FPGA and ZYNQ platforms, thereby helping to reduce system costs.

[0050] As an example, a frequency band partitioning link consists of two sub-frequency band links set up in parallel. DATA_X_M is input to its corresponding frequency band partitioning link, meaning DATA_X_M is input to two sub-frequency band links in parallel. In the first sub-frequency band link, DATA_X_M undergoes windowing and FFT transformation sequentially, then multiplied by the frequency domain coefficients of sub-frequency band 1 to extract the frequency band. Afterward, the extracted signal undergoes IFFT transformation and windowing sequentially, outputting the complex signal of sub-frequency band 1. In the second sub-frequency band link, DATA_X_M undergoes windowing and FFT transformation sequentially, then multiplied by the frequency domain coefficients of sub-frequency band 2 to extract the frequency band. Afterward, the extracted signal undergoes IFFT transformation and windowing sequentially, outputting the complex signal of sub-frequency band 2. The process of inputting DATA_X_S to its corresponding frequency band partitioning link is similar to that of DATA_X_M, and will not be described further here. The sub-band 1 signals from DATA_X_M and DATA_X_S are summed, and the sub-band 2 signals from DATA_Y_M and DATA_Y_S are summed. The output X-channel signal, after pulse compression, yields two complex signals, representing two parallel signals with different frequency components extracted from the original signal (X-channel signal). Similarly, the Y-channel signal is processed in the same way, resulting in two complex signals after pulse compression, also representing two parallel signals with different frequency components extracted from the original signal (Y-channel signal).

[0051] It should be noted that the above example of dividing a digital signal into two frequency bands is just one example. If computing resources (or FPGA resources if implemented in an FPGA) allow, it is also possible to divide a digital signal into three or four frequency bands.

[0052] Preferably, the preset interval is the pulse signal transmission interval. This further reduces the consumption of computing resources.

[0053] Preferably, the different frequency band signals under each pulse signal and the corresponding frequency band signals of the pulse signal at a preset distance are subjected to first-order differential processing to obtain the first-order differential result corresponding to each pulse signal, including: the different frequency band signals under the pulse signal are alternately stored in the first first-in-first-out memory and the second first-in-first-out memory according to the transmission order of the pulse signal.

[0054] like Figure 3As shown, the different frequency band signals under the current pulse signal are conjugated and then fed into the first FIFO1 memory and a complex multiplier. Simultaneously, the different frequency band signals under the previous pulse signal are read from the second FIFO2 memory and fed into the complex multiplier. The corresponding frequency band signals from the two pulse signals are multiplied in the complex multiplier to obtain the first-order difference result corresponding to the current pulse signal. Alternatively, the different frequency band signals under the current pulse signal are conjugated and then fed into the second FIFO2 memory and a complex multiplier. Simultaneously, the different frequency band signals under the previous pulse signal are read from the first FIFO1 memory and fed into the complex multiplier. The corresponding frequency band signals from the two pulse signals are multiplied in the complex multiplier to obtain the first-order difference result corresponding to the current pulse signal. Thus, the process of summing adjacent difference rotation vectors mostly involves multiplication and addition operations, requiring relatively few computational resources. This makes it suitable for deployment on FPGA and ZYNQ platforms, thereby reducing system costs.

[0055] S3. Perform arctan operation on each complex signal to solve for the phase angle, and expand the phase angle to obtain the phase signal of the sensing fiber under each pulse.

[0056] As an example, the phase signal of the sensing fiber under three pulses is as follows: Figure 4 As shown.

[0057] S4. Perform spatial differential processing on each phase signal to obtain the phase demodulation signal of the sensing fiber under each pulse.

[0058] The phase signal of the sensing fiber obtained in S3 under each pulse cannot well reflect the amount of phase change, so spatial differential processing is performed on each phase signal.

[0059] Specifically, based on a pre-set spatial differential distance, the difference between two sampling points that are spatially separated in each phase signal is calculated to obtain the phase demodulation signal of the sensing fiber under each pulse.

[0060] As an example, the preset spatial difference distance is 3, and the phase signal queues are 1, 2, 3, 4, 5, 6, 7, 8, 9, 10.... Based on the preset spatial difference distance, the difference between two sampling points in each phase signal that are spatially separated by the preset spatial difference distance is calculated. The operation performed is 4-1, 5-2, 6-3, 7-4, 8-5, 9-6, 10-7.... The resulting new signal queue is the phase demodulated signal.

[0061] As an example, for Figure 4 The phase signal in the image is spatially differentially processed to obtain the phase demodulated signal of the sensing fiber under each pulse, such as... Figure 5 As shown.

[0062] S5. Based on the pre-set fiber sampling positions, extract the sampling points corresponding to the fiber sampling positions in each phase demodulated signal, arrange all sampling points according to the sampling time, and obtain the vibration signal of the fiber sampling position; such as Figure 6 As shown, the vibration signal is sequentially windowed and FFT transformed. Then, the vibration signal is compensated for in the low-frequency domain according to the preset frequency domain compensation coefficient. After that, the frequency domain compensated vibration signal is sequentially transformed by IFFT and windowed, and the result is output.

[0063] For the short-time Fourier transform, a narrow window has high time resolution but low frequency resolution, while a wide window has low time resolution but high frequency resolution. The window length of the short-time Fourier transform is determined based on the range of low-frequency signals to be compensated.

[0064] Optionally, a sinusoidal window, rectangular window, Hanning window, or Hamming window can be used to window the vibration signal.

[0065] In summary, the first key point of the fiber optic DAS phase demodulation method provided in this invention is that: using two adjacent pulse detection signals (which can be polarized or unpolarized) as a reference for rotational vector summation can eliminate accumulated errors. After rotational vector summation, a frequency domain filter is introduced using short-time Fourier transform to recover the suppressed low-frequency signal, thereby achieving wide-bandwidth real-time detection of signals from extremely low to high frequencies, improving the accuracy and stability of signal processing. The second key point is that the fiber optic DAS phase demodulation method provided in this invention mostly involves multiplication and addition operations, and the multiplication operations can mostly be calculated using bit shifting, requiring very few computational resources. This makes it suitable for deployment on FPGA and ZYNQ platforms, enabling completely lower-level phase demodulation and significantly reducing system costs.

[0066] When the fiber optic DAS phase demodulation method provided in this embodiment of the invention is deployed on the ZYNQ platform, high-precision demodulation of the entire lower-level machine can be achieved through the PS and PL terminals of the ZYNQ.

[0067] This invention also provides an optical fiber DAS phase demodulation device, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program stored in the memory, it implements the steps of the optical fiber DAS phase demodulation method as described above.

[0068] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0069] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, as well as combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions.

[0070] It should be noted that any reference numerals placed between parentheses in the claims should not be construed as limiting the claims. The word "comprising" does not exclude the presence of components or steps not listed in the claims. The word "a" or "an" preceding a component does not exclude the presence of a plurality of such components. The invention can be implemented by means of hardware comprising several different components and by means of a suitably programmed computer. In claims that enumerate several means, several of these means may be embodied by the same hardware. The use of the terms first, second, third, etc., is merely for convenience of expression and does not indicate any order. These terms can be understood as part of the component names.

[0071] Furthermore, it should be noted that in the description of this specification, the terms "one embodiment," "some embodiments," "embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0072] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the claims should be interpreted to include both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0073] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, then this invention should also include these modifications and variations.

Claims

1. A fiber optic DAS phase demodulation method, characterized in that, Includes the following steps: S1. Acquire the digital signal under each pulse signal emitted by the sensing fiber in the DAS system; S2. After sub-band extraction and matched filtering of the digital signal under each pulse signal and the digital signal under the pulse signal at a preset interval, adjacent differential rotating vector summation is performed to obtain a complex signal; wherein, the preset interval is an integer multiple of the pulse signal transmission interval; S3. Perform arctan operation on each complex signal to solve for the phase angle, and expand the phase angle to obtain the phase signal of the sensing fiber under each pulse. S4. Perform spatial differential processing on each phase signal to obtain the phase demodulation signal of the sensing fiber under each pulse. S5. Based on the preset fiber sampling position, extract the sampling points corresponding to the fiber sampling position in each phase demodulation signal, arrange all sampling points according to the sampling time, and obtain the vibration signal of the fiber sampling position; perform windowing processing and FFT transformation on the vibration signal in sequence, then perform low-frequency domain compensation on the vibration signal according to the preset frequency domain compensation coefficient, and then perform IFFT transformation and windowing processing on the frequency domain compensated vibration signal in sequence, and output the result.

2. The fiber optic DAS phase demodulation method according to claim 1, characterized in that, The pulse signals transmitted by the DAS system are either single-frequency signals or swept-frequency signals.

3. The fiber optic DAS phase demodulation method according to claim 1, characterized in that, S2 includes: using the pulse intra-frequency division method to divide the digital signal under each pulse into a preset number of signals with different frequency bands, performing first-order differential processing on the signals with different frequency bands under each pulse signal and the corresponding frequency band signals of the pulse signal at a preset distance to obtain the first-order differential result corresponding to each pulse signal, and adding all the first-order differential results corresponding to each pulse signal to obtain the complex signal of the sensing fiber under each pulse.

4. The fiber optic DAS phase demodulation method according to claim 3, characterized in that, In S1, two backscattered Rayleigh light signals are acquired under each pulse signal emitted by the sensing fiber in the DAS system, and the two backscattered Rayleigh light signals are converted into two digital signals.

5. The fiber optic DAS phase demodulation method according to claim 4, characterized in that, The pulse intra-frequency division method is used to divide the digital signal under each pulse into a preset number of signals with different frequency bands, including: The two digital signals acquired by the sensing fiber under each pulse signal transmitted by the DAS system are the X-channel digital signal DATA_X_M and the Y-channel digital signal DATA_Y_M, respectively. Copy DATA_X_M to obtain DATA_X_S; copy DATA_Y_M to obtain DATA_Y_S; Input DATA_X_M, DATA_X_S, DATA_Y_M, and DATA_Y_S into their respective frequency band division links to obtain different frequency band signals corresponding to DATA_X_M, DATA_X_S, DATA_Y_M, and DATA_Y_S. Add the corresponding frequency band signals in DATA_X_M and DATA_X_S, and add the corresponding frequency band signals in DATA_Y_M and DATA_Y_S to output the different frequency band signals of the digital signal under each pulse; The frequency band division link includes at least two sub-frequency band links set in parallel, and the frequency domain coefficients of the at least two sub-frequency band links are different from each other; the signal is input to the sub-frequency band link, and the signal is sequentially windowed and FFT transformed. Then, the frequency band of the signal is extracted according to the pre-set sub-frequency band frequency domain coefficients. After that, the extracted signal is sequentially IFFT transformed and windowed, and the result is output.

6. The fiber optic DAS phase demodulation method according to claim 3, characterized in that, The preset interval is the pulse signal transmission interval.

7. The fiber optic DAS phase demodulation method according to claim 6, characterized in that, The first-order difference is performed between the different frequency band signals under each pulse signal and the corresponding frequency band signals of pulse signals at a preset interval to obtain the first-order difference result corresponding to each pulse signal, including: Signals of different frequency bands under pulse signals are alternately stored in the first first-in-first-out (FIFO) memory and the second first-in-first-out (FIFO) memory according to the transmission order of the pulse signals. The conjugate signals of different frequency bands under the current sub-pulse signal are sent to the first FIFO memory and the complex multiplier. Simultaneously, the signals of different frequency bands under the previous pulse signal are read from the second FIFO memory and sent to the complex multiplier. The corresponding frequency band signals from the two pulse signals are multiplied in the complex multiplier to obtain the first-order difference result corresponding to the current sub-pulse signal; or... The different frequency band signals under the current pulse signal are conjugated and sent to the second first-in-first-out memory and the complex multiplier. At the same time, the different frequency band signals under the previous pulse signal are read from the first first-in-first-out memory and sent to the complex multiplier. The corresponding frequency band signals in the two pulse signals are multiplied in the complex multiplier and output to obtain the first-order difference result corresponding to the current pulse signal.

8. The fiber optic DAS phase demodulation method according to claim 1, characterized in that, In S4, based on the preset spatial differential distance, the difference between two sampling points that are spatially different in each phase signal is calculated to obtain the phase demodulation signal of the sensing fiber under each pulse.

9. The fiber optic DAS phase demodulation method according to claim 1, characterized in that, In S5, a sinusoidal window, rectangular window, Hanning window, or Hamming window are used to window the vibration signal.

10. A fiber optic DAS phase demodulation device, characterized in that, The method includes a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program stored in the memory, it implements the steps of the fiber optic DAS phase demodulation method according to any one of claims 1 to 9.

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