A low-cost phase-discriminating phi-otdr system based on a single-chip microcomputer

Abstract

The application discloses a low-cost phase discrimination type system based on a single-chip microcomputer, comprising a narrow line width laser, an intensity modulator, an erbium-doped fiber amplifier, a circulator, a 1x2 coupler, a delay optical fiber, a 3x3 coupler, three photoelectric detectors, three sample-and-hold devices and a single-chip microcomputer. The application uses a low-cost microprocessor and sample-and-hold devices to replace original expensive devices, and cooperates with a special low-computational-phase demodulation algorithm, so that the system cost is reduced as much as possible without affecting the original system performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of distributed optical fiber sensing technology, in particular to a low-cost phase discrimination type φ-OTDR system based on a single-chip microcomputer. BACKGROUND

[0002] Distributed Acoustic Sensor (DAS) uses the whole optical fiber as the sensing medium and sensing unit, which can measure the parameter changes along the optical fiber in real time and continuously, and has the advantages of small size, anti-electromagnetic interference, and robustness in harsh environments. In many applications, especially in remote applications such as pipeline safety and harsh environments such as oil and gas wells, it is a very promising solution.

[0003] At present, the implementation of DAS system is mainly based on phase-sensitive Optical Time Domain Reflectometry (φ-OTDR), which detects the phase change of backscattered Rayleigh light in the sensing optical fiber to perceive external disturbance information. After the optical fiber is disturbed, the optical path at the corresponding position will change, resulting in a change in the phase difference of Rayleigh scattering light generated at both ends of the disturbed optical fiber. In theory, the phase difference of Rayleigh scattering light generated at both ends of the disturbed optical fiber has a linear relationship with the disturbance, so the quantitative measurement of the disturbance amplitude can be realized by demodulating the change of the phase difference, which is the sensing principle of DAS. According to the different demodulation phase modes, the DAS system structure mainly has heterodyne coherent detection, three-port coupling detection, and phase-generated carrier. Different demodulation algorithms have their own advantages and disadvantages. The phase demodulation based on 3x3 coupler (also known as low-cost phase discrimination type) is realized by introducing a 3x3 coupler with a 120° phase difference between the two arms and combining with an interference structure, which is suitable for direct detection of the optical path and has less influence on polarization noise, but has higher requirements for device consistency.

[0004] The traditional three-port coupling detection φ-OTDR system structure mainly includes indispensable optoelectronic devices such as narrow line width laser (NLL), acousto-optic modulator (AOM), erbium-doped fiber amplifier (EDFA), 3x3 coupler (OC), and three photodetectors (PD), as well as data acquisition and processing equipment such as data acquisition card (DAQ) and data processing end (generally PC).

[0005] In order to better and faster demodulate the phase information, high sampling rate data acquisition cards and high configuration and good performance PC devices are generally required, and such performance corresponding devices are often expensive, which makes the price of the whole DAS device high, limiting the use of DAS devices in some cost-sensitive application scenarios. SUMMARY

[0006] The present application aims at the problem of high cost of existing DAS equipment, and provides a low-cost phase-discrimination type phi-OTDR system based on a single-chip microcomputer.

[0007] To achieve the above object, the present application adopts the following technical scheme:

[0008] In a first aspect, the present application provides a low-cost phase-discrimination type phi-OTDR system based on a single-chip microcomputer, which comprises a narrow-linewidth laser, an intensity modulator, an erbium-doped fiber amplifier, a circulator, a 1x2 coupler, a delay fiber, a 3x3 coupler, three photodetectors, three sample-and-hold devices, and a single-chip microcomputer.

[0009] The input end of the intensity modulator is connected with the narrow-linewidth laser, and the output end is connected with the erbium-doped fiber amplifier. The intensity modulator is used for modulating continuous laser with high coherence characteristics generated by the narrow-linewidth laser source into corresponding pulsed light, and the repetition frequency, pulse width and triggering mechanism of the pulsed light are controlled by the single-chip microcomputer. The pulsed light emitted by the intensity modulator enters the circulator after being amplified by the erbium-doped fiber amplifier. One output end of the circulator is connected with the 1x2 coupler, and the other output end is connected with the optical fiber to be measured.

[0010] The 1x2 coupler equally divides the detection signals returned by the circulator into two detection lights with equal power. One of the two detection lights is delayed by the delay fiber and then incident on the 3x3 coupler together with the other detection light. The 3x3 coupler couples the two detection lights again and then equally divides them into three light signals.

[0011] The output ends of the three photodetectors are connected with the three sample-and-hold devices one by one. The three photodetectors have the same device parameters and convert the three light signals coupled by the 3x3 coupler into corresponding photocurrent signals and then output the photocurrent signals to the three sample-and-hold devices.

[0012] The output ends of the three sample-and-hold devices are connected with the single-chip microcomputer. Each sample-and-hold device samples the input photocurrent signal according to a preset sampling period, keeps the amplitude of the sampled photocurrent signal to the next sampling period, and then covers the amplitude of the photocurrent signal of the current sampling period with the amplitude of the photocurrent signal of the next sampling period.

[0013] The single-chip microcomputer stores a mapping relationship table of the photoelectric current signal amplitude and the phase variation amount caused by external disturbance, and receives the photoelectric current signal values sampled by the three sample-and-hold devices to calculate the estimated value of the optimal phase variation amount corresponding to the three photoelectric current signal amplitudes in the current sampling period in combination with the mapping relationship table.

[0014] Further, the single-chip microcomputer stores three mapping relationship tables, and the three mapping relationship tables correspond to the mapping relationship of the photoelectric current signal amplitude and the phase variation amount caused by external disturbance of the three sample-and-hold devices respectively.

[0015] Further, the process that the single-chip microcomputer calculates the estimated value of the optimal phase variation amount corresponding to the three photoelectric current signal amplitudes in the current sampling period in combination with the mapping relationship table includes the following steps:

[0016] Suppose the mapping relationship between the photoelectric current signal amplitude and the phase variation amount caused by external disturbance obtained by each sample-and-hold device is:

[0017]

[0018] Wherein, I N (m) is the mth photoelectric current signal amplitude in the lookup table corresponding to the Nth sample-and-hold device, is the phase variation amount caused by external disturbance in the lookup table corresponding to I N (m), N is the number of the sample-and-hold device, N=1, 2, 3, and M is the degree of phase refinement, the greater M is, the higher the phase accuracy is;

[0019] The three mapping relationships are combined:

[0020]

[0021] In the formula, is the photoelectric current signal amplitude sampled at t, is the square sum of the difference between the three photoelectric current signal amplitudes sampled at t and the amplitudes in the respective lookup tables;

[0022] The phase value corresponding to the m value with the minimum square sum of the difference is taken as the estimated value of the optimal phase variation amount at t.

[0023] Further, the single-chip microcomputer includes three storage blocks, and the three storage blocks correspond to the three sample-and-hold devices respectively, and each storage block has M rows, corresponding to the degree of phase variation refinement.

[0024] Further, the single-chip microcomputer adopts PIC16F914.

[0025] ​Further, the output light wavelength of the narrow linewidth laser is 1550nm, the linewidth is 100kHz, and the optical power is 8dbm.

[0026] Further, the single-chip microcomputer obtains the phase change values caused by external disturbances at different positions by repeatedly changing the delay time from the pulse light emission of the intensity modulator to the start of sampling of the sample holder, to perform distributed sensing measurement on external disturbances within a certain range.

[0027] In a second aspect, the application provides a working method of a low-cost phase-discrimination type phi-OTDR system based on a single-chip microcomputer, which comprises:

[0028] S1, modulating continuous laser with high coherence generated by a narrow linewidth laser into corresponding pulse light, and injecting the amplified pulse light into a circulator;

[0029] S2, when external disturbance applies vibration on any position of the fiber to be measured, the disturbance signal is transmitted reversely and enters a 1x2 coupler through the circulator, and the 1x2 coupler divides the two-way probe light with equal power, wherein one way of probe light is mixed with another way of probe light through a delay optical fiber;

[0030] S3, using a 3x3 coupler to divide the mixed signal into three-way signal light, and the three-way signal light is converted into corresponding photoelectric current signal through three photoelectric detectors respectively;

[0031] S4, controlling three sample holders to sample and hold the three-way photoelectric current signal according to a preset sampling period, matching the amplitude of the sampled photoelectric current signal with the corresponding mapping relationship table, and calculating the estimation value of the best phase change amount corresponding to the three-way photoelectric current signal amplitude of the current sampling period.

[0032] The application has the following advantages:

[0033] (1) The single-chip microcomputer and the sample holder are used to replace the original PC and DAQ, which are relatively expensive devices, and cooperate with a low-computing mapping relationship table (table lookup method) to reduce the system cost as much as possible without affecting the original system performance.

[0034] (2) The volume of the replacement module is much smaller than that of the original module, which provides a way for the miniaturization of DAS equipment in the future.

[0035] (3) A low-computing mapping relationship algorithm is used to reduce the requirement for the performance of the data processing module to a lower level while ensuring high-speed operation. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1It is a low-cost phase-detection type φ-OTDR system structure diagram based on a single-chip microcomputer according to an embodiment of the application.

[0037] Figure 2 It is an internal block diagram of a specific resource configuration of a single-chip microcomputer according to an embodiment of the application.

[0038] Figure 3a It is an amplitude information diagram obtained by a sample-and-hold device 1 in a sampling process.

[0039] Figure 3b It is an amplitude information diagram obtained by a sample-and-hold device 2 in a sampling process.

[0040] Figure 3c It is an amplitude information diagram obtained by a sample-and-hold device 3 in a sampling process.

[0041] Figure 4 It is a diagram of three amplitude-phase mapping relationships in a lookup table.

[0042] Figure 5a It is a diagram of a sinusoidal signal corresponding to external disturbance exerted by phase information before unwrapping.

[0043] Figure 5b It is a diagram of a sinusoidal signal corresponding to external disturbance exerted by phase information after unwrapping. DETAILED DESCRIPTION

[0044] The application will now be described in further detail with reference to the accompanying drawings.

[0045] Figure 1 It is a structure diagram of a low-cost phase-detection type φ-OTDR system based on a single-chip microcomputer according to the application. The system device comprises a narrow line width laser (NLL), an intensity modulator (MOD), an erbium-doped fiber amplifier (EDFA), a circulator (Cir), a 1x2 coupler (Coupler), a delay fiber (Fiber), a 3x3 coupler, three photoelectric detectors (PDs), three sample-and-hold devices (S / Hs), and a single-chip microcomputer (MCU).

[0046] The input end of the intensity modulator is connected with the narrow line width laser, and the output end is connected with the erbium-doped fiber amplifier. The intensity modulator is used for modulating continuous laser with high coherence characteristics generated by the narrow line width laser into corresponding pulsed light. The repetition frequency, pulse width and trigger mechanism of the pulsed light are controlled by the single-chip microcomputer. The pulsed light emitted by the intensity modulator enters the circulator after being amplified by the erbium-doped fiber amplifier. One of the output ends of the circulator is connected with the 1x2 coupler, and the other output end is connected with the fiber to be measured.

[0047] 1x2 coupler divides the detection signal returned by the circulator into two detection lights with equal power, one of which is delayed by a delay fiber and then enters the 3x3 coupler together with the other detection light, and the three light signals coupled by the 3x3 coupler are then divided into three light signals, which respectively enter three photodetectors.

[0048] The output ends of the three photodetectors are connected to three sample-and-hold devices one by one, and the three sample-and-hold devices have the same device parameters, and the three light signals coupled by the 3x3 coupler are converted into corresponding photocurrent signals and then output to the three sample-and-hold devices.

[0049] The output ends of the three sample-and-hold devices are connected to a single-chip microcomputer, each sample-and-hold device samples the input to-be-measured photocurrent signal according to a preset sampling period, and keeps the amplitude of the sampled photocurrent signal to the next sampling period, and then uses the amplitude of the photocurrent signal of the next sampling period to cover the amplitude of the photocurrent signal of the current sampling period. The essence of the sample-and-hold device in this embodiment is a timing analog-to-digital conversion pre-device, which takes the value of the to-be-measured signal at a certain point in time, keeps this signal value for a period of time for conversion by the analog-to-digital converter, and then takes another analog signal value at the next sampling time to replace the original value.

[0050] The single-chip microcomputer stores a mapping relationship table of the amplitudes of the photocurrent signals and the phase change amounts caused by external disturbances, and receives the amplitudes of the photocurrent signals sampled by the three sample-and-hold devices, and calculates the estimated value of the optimal phase change amount corresponding to the amplitudes of the three photocurrent signals in the current sampling period in combination with the mapping relationship table. The core of the single-chip microcomputer in this embodiment is a microprocessor, which is used to control the operation of the entire system.

[0051] Unlike the prior art, this embodiment can replace the original PC with a single-chip microcomputer with lower computing power, and replace the original data acquisition card with a sample-and-hold device, and cooperate with the aforementioned low-computing-phase demodulation algorithm to reduce the system cost as much as possible without affecting the performance of the original system. The following will describe several key technical solutions of this embodiment in detail in combination with the drawings.

[0052] (I) Phase demodulation algorithm

[0053] Phase demodulation is essentially a process of obtaining phase information from amplitude information. If the mapping relationship between amplitude and phase is determined in advance, phase demodulation can be completed through simple retrieval calculation, and the complex calculation process is omitted.

[0054] Through corresponding theoretical derivation and verification, the following conclusions are obtained: the mapping relationship between the amplitude I N (m) of the photocurrent signal obtained by each sample-and-hold device and the phase change amount caused by external disturbances is:

[0055]

[0056] wherein, I N (m) is the mth amplitude of the photocurrent signal corresponding to the Nth sample-and-hold device in the lookup table, is the phase change amount caused by the external disturbance corresponding to I N (m) in the lookup table, N is the number of the sample-and-hold device, N = 1, 2, 3, and M is the degree of phase refinement, the greater M is, the higher the phase accuracy is. The mapping relationship is not monotonic, and the amplitude and the phase are not a one-to-one correspondence. However, because there are three mapping relationships with a phase difference of 120°, the combined three mapping relationships can still obtain a unique phase change amount corresponding to the amplitude measured at the current time. The specific method is as follows:

[0057]

[0058] wherein, is the amplitude of the photocurrent signal sampled at t, is the sum of squares of differences between the amplitudes of the three photocurrent signals sampled at t and the amplitudes in the respective lookup tables;

[0059] the phase value corresponding to the m value with the minimum sum of squares of differences is taken as the estimated value of the optimal phase change amount at t.

[0060] Preferably, in order to adapt to the limited data storage depth and computing capacity of the single-chip microcomputer, a memory is used to store the three mapping relationship tables in advance, and the three mapping relationship tables correspond to the mapping relationships between the amplitudes of the photocurrent signals of the three sample-and-hold devices and the phase change amounts caused by the external disturbance. The memory can be divided into three storage blocks corresponding to the three sample-and-hold devices, and each storage block has M rows corresponding to the degree of refinement of the phase change amount. The amplitudes of the three sample-and-hold devices obtained at a certain time are searched in the M rows of storage data, and the corresponding sum of squares of differences is obtained, so that the phase value corresponding to the row with the minimum sum of squares of differences is the solution. This scheme can reduce the requirement for the performance of the data processing module to a lower level, while ensuring high-speed operation.

[0061] Exemplarily, the single-chip microcomputer adopts PIC16F914. The single-chip microcomputer has 7K on-chip FLASH and multi-channel 10-bit A / D. The internal block diagram of the specific resource configuration is as shown in Figure 2 The trigger pulse of the intensity modulator is captured by the CCP pin, and the ADC combines the on-chip analog multiplexer to realize polling collection of 3 signals after a delay generated by the timer Timer, and a part of the FLASH is used as the lookup table storage space.

[0062] ​The output light wavelength of the narrow line width laser is 1550 nm, the line width is 100 kHz, and the optical power is 8 dbm. The continuous light output by the NLL is modulated into pulsed light by the MOD, the width of the optical pulse is 100 ns, the repetition period is 37 us, and the corresponding spatial resolution is 10 m. The pulsed light is amplified by the EDFA and then injected into the sensing optical fiber through the circulator. The length of the sensing optical fiber is 2.16 km. It should be understood that the technical solution of the embodiment is not limited to the single-chip microcomputer or the laser with the above-mentioned parameters. The above-mentioned example is only used to make the technical solution more specific.

[0063] (ii) Distributed sensing measurement

[0064] As one of the preferred examples, the φ-OTDR system of the embodiment can realize distributed sensing measurement without adding any hardware device. Specifically, the time length between the emission of the probe pulse and the start of sampling by the sample holder is taken as the delay time, and the delay time multiplied by the speed of light is reflected to the spatial distance, so that the spatial position of the phase change value can be obtained by table lookup. Therefore, by changing the delay time, the phase change value caused by external disturbance at different positions can be obtained. By repeatedly changing the delay time, distributed sensing measurement of external disturbance within a certain range can be realized.

[0065] On the basis of the system structure, the embodiment of the application proposes a working method of a low-cost phase-discrimination type φ-OTDR system based on a single-chip microcomputer, which comprises the following steps:

[0066] S1, the continuous laser with high coherence generated by the narrow line width laser is modulated into corresponding pulsed light, and the pulsed light is amplified and then injected into the circulator.

[0067] S2, when external disturbance applies vibration at any position of the to-be-measured optical fiber, the disturbance signal is transmitted reversely and enters the 1x2 coupler through the circulator, and the 1x2 coupler divides the two probe lights with equal power. One of the two probe lights is mixed with the other probe light through the delay optical fiber.

[0068] S3, the 3x3 coupler divides the mixed signal into three signal lights, and the three signal lights are converted into corresponding photocurrent signals by the three photodetectors.

[0069] S4, the three sample holders simultaneously sample and hold the three photocurrent signals according to the preset sampling period, the amplitudes of the sampled photocurrent signals are matched with the corresponding mapping table, and the estimation value of the optimal phase change amount corresponding to the three photocurrent signal amplitudes of the current sampling period is calculated. The working principle of the foregoing φ-OTDR system is described in detail through a specific example.

[0070] The specific working steps of the present φ-OTDR system are as follows:

[0071] Step one, intensity modulator MOD is used to modulate the continuous laser with high coherence characteristics generated by the narrow linewidth laser (output constant power is 8dBm, center wavelength is 1550nm) into corresponding pulsed light (pulse width is 100ns, repetition period is 37us), and the pulsed light is amplified and injected into the circulator.

[0072] Step two, assuming that the external disturbance applies a sinusoidal vibration signal with a vibration frequency of 100Hz and an amplitude of 13V at the 1.553km fiber to be measured, the disturbance signal is transmitted in the opposite direction and enters the 1x2 coupler through the circulator, and the 1x2 coupler divides the two equal power detection lights, one of which passes through the 200m delay fiber and the other of which mixes with the other.

[0073] Step three, a 3x3 coupler is used to divide the mixed signal into three signal lights, and the three signal lights are converted into corresponding photocurrent signals through three photoelectric detectors with a bandwidth of 10MHz.

[0074] Step four, control three sample and hold devices to sample and hold the three photocurrent signals according to the preset sampling period at the same time, match the amplitude of the sampled photocurrent signal with the corresponding mapping table, and calculate the estimated value of the best phase change corresponding to the three photocurrent signal amplitudes in the current sampling period.

[0075] Step five, the single-chip microcomputer controls the three sample and hold devices to sample synchronously after about 15.5us (the time corresponding to the spatial distance of the external disturbance is generated by using the timer on the single-chip microcomputer) after the detection pulse is sent, and the sampling period is 37us (corresponding to the repetition period of the detection pulse, which is greater than the minimum conversion period of the on-chip A / D 17.6us), and after continuous sampling for 0.2s, the amplitude information of the three sample and hold device ports is recorded, as shown in Figures 3a to 3c , in order to distinguish, the three sample and hold devices are recorded as sample and hold device 1, sample and hold device 2 and sample and hold device 3, and the three photoelectric detectors are recorded as photoelectric detector 1, photoelectric detector 2 and photoelectric detector 3. Corresponding to the lookup table Figure 4 , the corresponding phase information is obtained, as shown in Figure 5a and Figure 5b . Here, M=360, the phase accuracy is 1°, the amplitude data width is 14 bits, and the total lookup table size is not more than 2K, which is stored in the on-chip FLASH.

[0076] The above are only preferred embodiments of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiments. Any technical scheme falling within the concept of the present application shall fall within the protection scope of the present application. It should be noted that, for ordinary skilled in the art, some improvements and refinements without departing from the principles of the present application shall be considered as the protection scope of the present application.

Claims

1. A low-cost phase-discriminating φ-OTDR system based on a single-chip microcomputer, characterized by, The φ-OTDR system comprises a narrow linewidth laser, an intensity modulator, an erbium-doped fiber amplifier, a circulator, a 1x2 coupler, a delay fiber, a 3x3 coupler, three photodetectors, three sample-and-hold devices and a single-chip microcomputer. The input end of the intensity modulator is connected with the narrow linewidth laser, and the output end is connected with the erbium-doped fiber amplifier; the intensity modulator is used for modulating continuous laser with high coherence generated by the narrow linewidth laser into corresponding pulsed light, and the repetition frequency, pulse width and triggering mechanism of the pulsed light are controlled by the single-chip microcomputer; the pulsed light emitted by the intensity modulator enters the circulator after being amplified by the erbium-doped fiber amplifier; one of the output ends of the circulator is connected with the 1x2 coupler, and the other output end is connected with the optical fiber to be measured. The 1x2 coupler divides the detection signals returned by the circulator into two detection lights with equal power, one of which is delayed by the delay fiber and then incident to the 3x3 coupler together with the other detection light; the three light signals coupled by the 3x3 coupler are divided into three light signals again, and the three light signals are incident to the three photodetectors, respectively. The output ends of the three photodetectors are connected with the three sample-and-hold devices one by one, and the device parameters of the three photodetectors are the same; the three light signals coupled by the 3x3 coupler are converted into corresponding photocurrent signals and then output to the three sample-and-hold devices. The output ends of the three sample-and-hold devices are connected with the single-chip microcomputer; each sample-and-hold device samples the input optical current signal according to a preset sampling period, and keeps the amplitude of the sampled optical current signal to the next sampling period; the amplitude of the optical current signal of the next sampling period is used to cover the amplitude of the optical current signal of the current sampling period. The single-chip microcomputer stores a mapping relationship table of the amplitudes of the optical current signals and the phase change amounts caused by external disturbances; the single-chip microcomputer receives the amplitudes of the optical current signals sampled by the three sample-and-hold devices, and calculates the estimated value of the optimal phase change amount corresponding to the three amplitudes of the optical current signals of the current sampling period according to the mapping relationship table.

2. The low-cost, phase-discriminating, monolithic microcontroller-based φ-OTDR system of claim 1, wherein, The single-chip microcomputer stores three mapping relationship tables, and the three mapping relationship tables correspond to the mapping relationship between the amplitudes of the optical current signals of the three sample-and-hold devices and the phase change amounts caused by external disturbances.

3. The low-cost, phase-discriminating, monolithic microcontroller-based φ-OTDR system of claim 2, wherein, The process of the single-chip microcomputer calculating the estimated value of the optimal phase change amount corresponding to the three amplitudes of the optical current signals of the current sampling period according to the mapping relationship table comprises the following steps: the mapping relationship between the amplitude of the optical current signal and the phase change amount caused by external disturbances obtained by each sample-and-hold device is: wherein I N (m) is the amplitude of the photocurrent signal corresponding to the mth lookup table of the Nth sample-and-hold device, is the phase change amount caused by the external disturbance corresponding to I N (m) in the lookup table, N is the number of the sample-and-hold device, N = 1, 2, 3, and M is the degree of phase refinement, the greater the value of M, the higher the phase accuracy. the three mapping relationships are combined: In the formula, is the amplitude of the light current signal sampled at time t, is the sum of the square of the difference between the amplitude of the three light current signals sampled at time t and the amplitude of the respective lookup table. The phase value corresponding to the m value of the minimum sum of squares of differences as an estimate of the optimum phase change amount at time t.

4. The low-cost, phase-discriminating, monolithic microcontroller-based φ-OTDR system of claim 3, wherein, The single-chip microcomputer comprises three storage blocks corresponding to the three sample-and-hold devices, and each storage block has M rows corresponding to the refinement degree of the phase change amount.

5. The low cost, microcontroller-based, phase-discriminator type, φ-0TDR system of claim 1, wherein, The single-chip microcomputer repeatedly changes the delay time from the pulsed light emitted by the intensity modulator to the start of sampling by the sample-and-hold device to obtain the phase change values caused by external disturbances at different positions, so as to perform distributed sensing measurement on external disturbances within a certain range.

6. A method of operating a φ-OTDR system as claimed in any one of claims 1 to 5, characterized in that The working method comprises: S1, the continuous laser with high coherence characteristics generated by the narrow linewidth laser is modulated into corresponding pulse light, and the pulse light is amplified and injected into a circulator; S2, when external disturbance applies vibration on any position of the to-be-measured optical fiber, the disturbance signal is reversely transmitted and enters a 1x2 coupler through the circulator, and the disturbance signal is equally divided into two detection lights with equal power by the 1x2 coupler, wherein one detection light passes through a delay optical fiber and mixes with the other detection light; S3, a 3x3 coupler is used to equally divide the mixed signal into three signal lights, and the three signal lights are respectively converted into corresponding photocurrent signals by three photodetectors; S4, three sample-and-hold devices are controlled to simultaneously sample and hold the three photocurrent signals according to a preset sampling period, the amplitudes of the sampled photocurrent signals are matched with a corresponding mapping table, and an estimation value of the best phase change amount corresponding to the three photocurrent signal amplitudes in the current sampling period is calculated.

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