Multi-resolution distributed optical fiber sound wave sensing method based on multi-order sideband

Abstract

The invention provides a multi-order sideband-based multi-resolution distributed optical fiber acoustic wave sensing method, which comprises the following steps of: generating a detection light pulse comprising a plurality of linear frequency modulation sidebands with different sweep bandwidths, and injecting the detection light pulse into a sensing optical fiber; receiving a Rayleigh backscattering signal generated in the sensing optical fiber to obtain an electric signal containing vibration information distributed along the sensing optical fiber; matching filter banks corresponding to a plurality of linear frequency modulation sidebands with different frequency sweeping bandwidths are adopted, parallel matching filtering processing is carried out on the electric signals, a plurality of distributed sound wave sensing signals with different spatial resolutions are decoupled from the electric signals, and the spatial resolutions are determined by the frequency sweeping bandwidths corresponding to the linear frequency modulation sidebands; based on a plurality of distributed sound wave sensing signals with different spatial resolutions, multi-resolution sound wave vibration monitoring along a sensing optical fiber is realized.

Description

Technical Field

[0001] This disclosure relates to the field of fiber optic sensing technology, and more specifically, to a multi-resolution distributed fiber optic acoustic wave sensing method based on multi-order sidebands. Background Technology

[0002] In recent years, Distributed Optical Fiber Sensing (DOFS) technology has been widely applied in fields such as seismic wave detection, pipeline safety monitoring, and perimeter security due to its advantages in long-distance continuous monitoring, real-time response, and high measurement accuracy. Among them, Distributed Acoustic Sensing (DAS) technology is particularly prominent, and Phase-sensitive Optical Time Domain Reflectometry (Φ-OTDR) based on high-coherence narrow-linewidth lasers has become the mainstream technical solution due to its high sensitivity to vibration and strain.

[0003] The spatial resolution of traditional Φ-OTDR systems is limited by the detection pulse width: to achieve high resolution, narrow pulses are required, but this leads to a decrease in pulse energy and a deterioration in the signal-to-noise ratio, creating a contradiction between spatial resolution and sensing distance, which restricts its application in long-distance, high-precision monitoring.

[0004] To overcome this limitation, pulse compression technology was introduced into the Φ-OTDR system. This technology, drawing inspiration from radar principles, injects a linearly frequency-modulated wide pulse and performs matched filtering on the backscattered signal, compressing the wide pulse into a narrow pulse in the time domain. Under this mechanism, spatial resolution is determined by the modulation bandwidth, rather than the actual pulse width, thus effectively resolving the contradiction between high resolution and high pulse energy, significantly improving measurement distance and positioning accuracy.

[0005] Frequency diversity techniques, such as frequency division multiplexing, are also applied in distributed optical fiber sensing. By injecting multiple frequency detection signals into the same optical fiber, parallel multi-path detection can be achieved, expanding the system's frequency response range and suppressing signal fluctuations caused by coherent fading.

[0006] In practical engineering, different spatial resolutions are often required for the same monitoring scenario: high resolution is used to accurately locate minute vibrations and identify structural defects, while low resolution is suitable for large-scale monitoring and regional early warning. However, existing technologies cannot meet the needs of multiple resolutions in a single measurement. Adjusting the resolution requires changing modulation parameters or repeating tests, resulting in insufficient system flexibility and low measurement efficiency.

[0007] Therefore, how to achieve parallel acquisition of multiple spatial resolutions in a single measurement has become a key technical problem that urgently needs to be solved. Developing new technologies that can simultaneously output multi-resolution sensing signals is of great significance for improving the scenario adaptability and engineering practical value of DAS systems. Summary of the Invention

[0008] In view of this, this disclosure provides a multi-resolution distributed optical fiber acoustic wave sensing method based on multi-order sidebands.

[0009] One aspect of this disclosure provides a multi-resolution distributed optical fiber acoustic wave sensing method based on multiple sidebands, comprising: S1, generating a probe light pulse containing multiple linear frequency modulated sidebands with different sweep bandwidths, and injecting the probe light pulse into a sensing optical fiber; S2, receiving a Rayleigh backscattered signal generated in the sensing optical fiber to obtain an electrical signal containing vibration information distributed along the sensing optical fiber; S3, performing parallel matched filtering processing on the electrical signal using matched filter banks corresponding to the multiple linear frequency modulated sidebands with different sweep bandwidths, decoupling multiple distributed acoustic wave sensing signals with different spatial resolutions from the electrical signal, wherein the spatial resolution is determined by the sweep bandwidth of the corresponding linear frequency modulated sideband; S4, realizing multi-resolution acoustic wave vibration monitoring along the sensing optical fiber based on the multiple distributed acoustic wave sensing signals with different spatial resolutions.

[0010] According to embodiments of this disclosure, generating a probe light pulse containing multiple linear frequency modulated sidebands with different sweep bandwidths includes: superimposing multiple linear frequency modulated electrical signals with different initial frequencies and sweep bandwidths to form a composite electro-modulation signal; and using the composite electro-modulation signal to drive an electro-optic modulator to modulate a continuous laser to generate the probe light pulse.

[0011] According to embodiments of this disclosure, the sweep bandwidths of the plurality of linear frequency modulated electrical signals are integer multiples of each other, and the linear frequency modulated electrical signals do not overlap in the frequency domain.

[0012] According to embodiments of this disclosure, the method further includes:

[0013] By presetting the amplitude of each of the linear frequency modulated electrical signals, the energy of each sideband in the probe optical pulse is balanced.

[0014] According to an embodiment of this disclosure, demodulating the Rayleigh backscattered signal generated in the sensing fiber includes: beating the Rayleigh backscattered light with a local oscillator light; and converting the beat-frequency optical signal into the electrical signal using a photodetector.

[0015] According to embodiments of this disclosure, the step of using matched filter banks corresponding to the plurality of linear frequency modulation sidebands with different sweep bandwidths to perform parallel matched filtering processing on the electrical signal, and decoupling multiple distributed acoustic wave sensing signals with different spatial resolutions from the electrical signal, includes: constructing a corresponding matched filter for each linear frequency modulation sideband, wherein the impulse response of the matched filter is the conjugate inversion of the ideal time-domain waveform of the sideband, and the frequency response range of the matched filter corresponds to the frequency range of the sideband; performing convolution operations on the electrical signal and each matched filter in the constructed matched filter bank to obtain a set of pulse compressed signals; wherein each pulse compressed signal constitutes a distributed acoustic wave sensing signal with a specific spatial resolution, and the spatial resolution of different pulse compressed signals is determined by the sweep bandwidth of the linear frequency modulation sideband of its corresponding matched filter.

[0016] According to embodiments of this disclosure, the multi-resolution acoustic vibration monitoring along the sensing optical fiber based on the plurality of distributed acoustic wave sensing signals with different spatial resolutions includes: extracting phase information of the plurality of distributed acoustic wave sensing signals with different spatial resolutions, and performing differential processing on the phase information to obtain differential phase signals; repeating steps S1 to S3 to obtain the plurality of differential phase signals that change over time; and generating a differential phase waterfall plot based on the differential phase signals that change over time to achieve the localization and waveform recovery of acoustic vibration events distributed along the optical fiber.

[0017] According to an embodiment of this disclosure, between steps S1 and S2, the method further includes: controlling the repetition frequency of the probe light pulse so that the pulse period of the probe light pulse is greater than the round-trip time of the probe light pulse in the sensing optical fiber.

[0018] According to the embodiments of this disclosure, because a combination of multi-level sideband modulation and parallel matched filtering is used, multiple acoustic wave sensing signals with different spatial resolutions can be decoupled from the composite detection signal in a single measurement. Therefore, it at least partially overcomes the technical bottleneck of traditional distributed fiber optic acoustic wave sensing systems, which are unable to simultaneously achieve high-resolution precise positioning and low-resolution large-area monitoring in a single measurement, as well as the inefficiency caused by adjusting hardware parameters or repeated measurements in the prior art when adjusting spatial resolution. Thus, it achieves the technical effect of acquiring multi-level spatial resolution signals in parallel during a single detection process, significantly improving system flexibility and measurement efficiency, and meeting the different accuracy monitoring requirements in complex scenarios. Attached Figure Description

[0019] The above and other objects, features and advantages of this disclosure will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0020] A flowchart illustrating a multi-resolution distributed fiber optic acoustic wave sensing method based on multi-order sidebands according to an embodiment of the present disclosure is shown schematically.

[0021] A schematic diagram of a multi-resolution distributed fiber optic acoustic wave sensing system based on multi-order sidebands according to an embodiment of the present disclosure is shown.

[0022] The spectrum of a modulator output signal containing multiple sidebands according to an embodiment of the present disclosure is schematically shown;

[0023] The time-domain waveform of the modulator output signal according to an embodiment of the present disclosure is schematically shown;

[0024] The output results of different matched filters according to embodiments of this disclosure are illustrated schematically;

[0025] A differential phase waterfall plot near the vibration region according to an embodiment of the present disclosure is schematically shown. Detailed Implementation

[0026] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0027] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0028] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0029] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0030] like Figure 1 As shown, this disclosure provides a multi-resolution distributed optical fiber acoustic wave sensing method based on multi-order sidebands, including steps S1 to S4.

[0031] S1 generates a probe light pulse containing multiple linear frequency modulated sidebands with different sweep bandwidths and injects the probe light pulse into the sensing fiber.

[0032] S2 receives the Rayleigh backscattered signal generated in the sensing fiber and interferes with the local oscillator light to obtain an electrical signal containing vibration information distributed along the sensing fiber.

[0033] S3 employs matched filter banks corresponding to multiple linear frequency modulation sidebands with different sweep bandwidths to perform parallel matched filtering on the electrical signal, thereby decoupling multiple distributed acoustic wave sensing signals with different spatial resolutions from the electrical signal. The spatial resolution is determined by the sweep bandwidth of the corresponding linear frequency modulation sideband.

[0034] S4 enables multi-resolution acoustic vibration monitoring along the sensing fiber by using multiple distributed acoustic wave sensing signals with different spatial resolutions.

[0035] like Figure 2As shown, this disclosure provides a system for implementing a multi-resolution distributed fiber optic acoustic wave sensing method based on multi-order sidebands. The system mainly includes a light source module 16, a signal modulation module 17, a sensing fiber 9, and a coherent receiving and signal processing module 18. The light source module 16 includes a narrow-linewidth laser 1, an optical isolator 2, and a 1:90 optical coupler 3 to generate probe light and local oscillator light. The signal modulation module 17 includes an electro-optic modulator 4, a 1:99 optical coupler 5, an acousto-optic modulator 6, a bias controller 10, and a signal generator 11. It uses multi-order sideband modulation to modulate the probe light signal into pulsed light containing multiple swept sidebands. The probe pulsed light is amplified by an optical amplifier 7 and injected into the sensing fiber 9 through a circulator 8. The backscattered Rayleigh light generated in the sensing fiber 9 passes through the circulator again. The optical amplifier 12 and the optical receiver 12 enter the coherent receiving and signal processing module 18. The coherent receiving and signal processing module 18 includes a 50:50 optical coupler 13, a balanced photodetector 14, and a signal acquisition module 15. In this module, the backscattered Rayleigh light beats with the local oscillator light to generate a beat frequency optical signal, which is converted into an electrical signal by the photodetector 14 and received by the signal acquisition module 15. Finally, the matched filtering method and the differential phase method are used for data processing to generate a differential phase curve and a waterfall plot, so as to realize the accurate positioning and waveform recovery of the vibration event.

[0036] The following is a detailed description of the multi-resolution distributed fiber optic acoustic wave sensing method based on multi-order sidebands provided in the embodiments of this disclosure.

[0037] S1 generates a probe light pulse containing multiple linear frequency modulated sidebands with different sweep bandwidths and injects the probe light pulse into the sensing fiber.

[0038] In this embodiment, multiple linear frequency modulated electrical signals with different initial frequencies and sweep bandwidths are superimposed to form a composite electromodulation signal. The composite electromodulation signal is used to drive an electro-optic modulator to modulate a continuous laser to generate a probe light pulse. The sweep bandwidths of the multiple linear frequency modulated electrical signals are integer multiples of each other, and the linear frequency modulated electrical signals do not overlap in the frequency domain.

[0039] A linearly chirped pulse (i.e., a probe pulse) can be generated by modulating continuous light emitted from a laser using an electro-optic modulator (EOM). The output light field after passing through the electro-optic modulator can be described as follows:

[0040]

[0041] in, For the input light field, To modulate electrical signals, It is a half-wave voltage.

[0042] The desired output optical field can be generated by controlling the composite modulated electrical signal. For typical multi-frequency carrier modulation (FDM), the modulated electrical signal is composed of multiple single-frequency carriers superimposed, and its form is as follows:

[0043]

[0044] in, The fundamental frequency, and The first The amplitude and initial phase of each carrier wave. Precise adjustment. and Furthermore, by utilizing the nonlinear effect of the modulator, several equal-amplitude comb-shaped spectra can be generated. For example, by setting relevant parameters, an optical frequency comb containing seven equal-amplitude spectral lines can be realized.

[0045] To achieve multi-resolution detection, the above-mentioned modulation signal needs to be extended into a superposition of multiple linear frequency modulated signals:

[0046]

[0047] While retaining the above and Consistency will result in multi-order sidebands with the same energy:

[0048]

[0049] in, and These represent the amplitude and initial phase of each linear frequency modulation sideband of the output signal, respectively.

[0050] like The spectrum of the probe light pulse is shown. Due to spectral leakage caused by the finite time window, there is uneven amplitude in multiple sidebands, which is corrected by moving average processing.

[0051] In this embodiment of the disclosure, step S1 involves presetting the amplitude of each linear frequency modulated electrical signal to achieve energy balance in each sideband of the probe light pulse.

[0052] For linear chirped pulse signals (i.e., linear frequency modulated electrical signals):

[0053]

[0054] The total signal energy is:

[0055]

[0056] Meanwhile, because the energy of a linear frequency modulated signal is uniformly distributed within the frequency range and its spectrum is approximately rectangular, its energy can be expressed as:

[0057]

[0058] Where H is the spectral amplitude. For bandwidth.

[0059] According to Parseval's theorem, energy satisfies the following equation in both the time and frequency domains:

[0060]

[0061] so:

[0062]

[0063] For cases where multiple frequency sweep signals are superimposed:

[0064]

[0065] Each sideband bandwidth is respectively …(Assuming the frequency ranges of different sidebands do not overlap). To ensure consistent output waveform energy after matched filtering in each sideband, the total energy of each sideband must be equal. Since the duration of the sidebands is consistent, only the amplitude needs to be equal. According to the above formula, the amplitude ratio of the spectrum at this time is… ,and The results are consistent, indicating that the scheme can achieve energy output such as multi-sideband.

[0066] In this embodiment of the disclosure, in step S1, the maximum repetition frequency of the probe light pulse is inversely proportional to the length of the optical fiber. The repetition frequency of the probe light pulse needs to be controlled according to the length of the optical fiber so that the pulse period of the probe light pulse is greater than the round-trip time of the probe light pulse in the sensing optical fiber, so as to avoid the pulse period being less than the round-trip time of the pulse in the optical fiber, which would lead to crosstalk.

[0067] S2 receives the Rayleigh backscattered signal generated in the sensing fiber to obtain an electrical signal containing vibration information distributed along the sensing fiber.

[0068] The Rayleigh backscattered signal generated in the demodulated sensing fiber includes: beating the Rayleigh backscattered light with the local oscillator light; and converting the beat-frequency optical signal into an electrical signal using a photodetector.

[0069] The frequency range of the backscattered signal is the same as that of the incident light, while the frequency range of the incident light is determined by the modulation signal of the modulator.

[0070] Control modulation signal , so that:

[0071]

[0072] in, , , , Set the fundamental frequency. Sweep bandwidth (T is the pulse width).

[0073] At this point, the modulator's output signal (i.e., the probe light pulse) actually contains three chirped sidebands of equal amplitude, with frequency ranges of 30-40MHz, 60-80MHz, and 90-120MHz. For example... The figure shows the time-domain waveform of the modulator output signal.

[0074] In this embodiment of the disclosure, in step S2, the signal generator that generates the electro-optic modulator driving signal and the signal acquisition card that receives the output signal of the photodetector use the same external trigger source; the trigger delay of both is controlled to ensure that the signal acquisition card acquires the scattered signal of the light pulse within a complete cycle.

[0075] S3 employs matched filter banks corresponding to multiple linear frequency modulation sidebands with different sweep bandwidths to perform parallel matched filtering on the electrical signal, thereby decoupling multiple distributed acoustic wave sensing signals with different spatial resolutions from the electrical signal. The spatial resolution is determined by the sweep bandwidth of the corresponding linear frequency modulation sideband.

[0076] In this embodiment of the disclosure, a corresponding matched filter is constructed for each linear frequency modulation sideband, wherein the impulse response of the matched filter is the conjugate inversion of the ideal time-domain waveform of the sideband, and the frequency response range of the matched filter corresponds to the frequency range of the sideband.

[0077] In this embodiment, step S3 involves using different matched filters whose frequency ranges correspond to different sidebands of the modulation signal. Chirped signals in three frequency ranges—30-40MHz, 60-80MHz, and 90-120MHz—are used as matched filters for... The obtained modulator output signal is subjected to matched filtering to obtain .

[0078] The main lobe half-widths of the three filters are 0.12 μs, 0.06 μs and 0.04 μs, respectively, which translate to spatial resolutions of approximately 12.0 m, 6.0 m and 4.0 m, thus achieving multiple spatial resolutions.

[0079] In this embodiment of the disclosure, step S3 involves performing a convolution operation between the electrical signal of the Rayleigh backscattered signal and each matched filter in the constructed matched filter bank to obtain a set of pulse compressed signals. S3 includes:

[0080] S3-1, Construct the complex form of the ideal reference chirped pulse signal, perform conjugate inversion, and obtain the matched filter;

[0081] In step S3-2, the Rayleigh scattering signal is convolved with the matched filter to obtain the matched filter compressed signal. Each pulse compressed signal constitutes a distributed acoustic wave sensing signal with a specific spatial resolution, and the spatial resolution of different pulse compressed signals is determined by the linear frequency modulation sideband sweep bandwidth of their corresponding matched filter.

[0082] The pulse duration of the matched-filtered signal is defined as the full width at half maximum (FWHM) of its main lobe, and its magnitude is inversely proportional to the total bandwidth of the sweep frequency; the spatial resolution is determined according to the sweep frequency bandwidth of each sideband. Where B is the bandwidth of each sideband, c is the speed of light, and n is the refractive index of the optical fiber.

[0083] S4 enables multi-resolution acoustic vibration monitoring along the sensing fiber by using multiple distributed acoustic wave sensing signals with different spatial resolutions.

[0084] S4 includes operations S4-1 to S4-3.

[0085] S4-1: Extract phase information from multiple distributed acoustic wave sensing signals with different spatial resolutions, and perform differential processing on the phase information to obtain differential phase signals.

[0086] S4-2, Repeat steps S1 to S3 to obtain multiple differential phase signals that change over time.

[0087] S4-3 generates a differential phase waterfall plot based on the time-varying differential phase signal to achieve the localization and waveform recovery of acoustic vibration events distributed along the optical fiber.

[0088] In this embodiment of the disclosure, the differential phase waterfall diagram is as follows: Figure 6 As shown.

[0089] According to the method provided in this disclosure, during a single measurement process, the combination of multi-order sidebands and multiple sets of matched filters enables the parallel acquisition of distributed acoustic signals with multiple spatial resolutions, significantly improving the flexibility and applicability of the sensing system in different application scenarios. Furthermore, this method achieves spatial resolution selection and adjustment solely through algorithms, without requiring the addition or modification of hardware, reducing system complexity and cost, and improving data processing efficiency and real-time performance. This provides strong support for the multi-scenario deployment and application of distributed fiber optic acoustic sensing technology.

[0090] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A multi-resolution distributed fiber optic acoustic wave sensing method based on multi-order sidebands, characterized in that, include: S1, generate a probe light pulse containing multiple linear frequency modulated sidebands with different sweep bandwidths, and inject the probe light pulse into the sensing fiber; S2, receive the Rayleigh backscattered signal generated in the sensing fiber and interfere with the local oscillator light to obtain an electrical signal containing vibration information distributed along the sensing fiber. S3, using matched filter banks corresponding to the multiple linear frequency modulation sidebands with different sweep bandwidths respectively, parallel matched filtering processing is performed on the electrical signal to decouple multiple distributed acoustic wave sensing signals with different spatial resolutions from the electrical signal, wherein the spatial resolution is determined by the sweep bandwidth of the corresponding linear frequency modulation sideband; S4. Based on the multiple distributed acoustic wave sensing signals with different spatial resolutions, multi-resolution acoustic wave vibration monitoring along the sensing optical fiber is realized.

2. The method according to claim 1, characterized in that, The generation of the probe light pulse containing multiple linear frequency-modulated sidebands with different sweep bandwidths includes: Multiple linear frequency modulated electrical signals with different initial frequencies and sweep bandwidths are superimposed to form a composite electrical modulation signal; The composite electro-modulation signal is used to drive an electro-optic modulator to modulate a continuous laser beam to generate the probe light pulse.

3. The method according to claim 2, characterized in that, The sweep bandwidths of the plurality of linear frequency modulated electrical signals are integer multiples of each other, and the linear frequency modulated electrical signals do not overlap with each other in the frequency domain.

4. The method according to claim 2, characterized in that, The method further includes: By presetting the amplitude and phase of each of the linear frequency modulated electrical signals, the energy of each sideband in the probe light pulse is balanced.

5. The method according to claim 1, characterized in that, The demodulation of the Rayleigh backscattered signal generated in the sensing fiber includes: The Rayleigh backscattered light is beat-frequencyed with the local oscillator light; The optical signal after frequency capture is converted into an electrical signal by a photodetector.

6. The method according to claim 1, characterized in that, The step of using matched filter banks corresponding to the multiple linear frequency modulation sidebands with different sweep bandwidths to perform parallel matched filtering processing on the electrical signal, and decoupling multiple distributed acoustic wave sensing signals with different spatial resolutions from the electrical signal, includes: For each of the linear frequency modulation sidebands, a corresponding matched filter is constructed, wherein the impulse response of the matched filter is the conjugate inversion of the ideal time-domain waveform of the sideband, and the frequency response range of the matched filter corresponds to the frequency range of the sideband. The electrical signal is convolved with each matched filter in the constructed matched filter bank to obtain a set of pulse compressed signals. Each of the pulse compression signals constitutes a distributed acoustic wave sensing signal with a specific spatial resolution, and the spatial resolution of different pulse compression signals is determined by the linear frequency modulation sideband sweep bandwidth of their corresponding matched filters.

7. The method according to claim 1, characterized in that, The multi-resolution acoustic vibration monitoring along the sensing optical fiber based on the multiple distributed acoustic wave sensing signals with different spatial resolutions includes: Phase information of the multiple distributed acoustic wave sensing signals with different spatial resolutions is extracted, and differential processing is performed on the phase information to obtain differential phase signals; Repeat steps S1 to S3 to acquire multiple differential phase signals that vary over time; Based on the time-varying differential phase signal, a differential phase waterfall plot is generated to enable the localization and waveform recovery of acoustic vibration events distributed along the optical fiber.

8. The method according to claim 1, characterized in that, Between steps S1 and S2, the method further includes: The repetition frequency of the probe light pulse is controlled such that the pulse period of the probe light pulse is greater than the round-trip time of the probe light pulse in the sensing optical fiber.

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