Self-adaptive multi-pulse-width pulse DAS method and system based on discrete scattering enhanced optical fiber

Abstract

The invention discloses a self-adaptive multi-pulse-width pulse DAS method and system based on a discrete scattering enhanced optical fiber. The system comprises a narrow linewidth laser, a first coupler, an acousto-optic modulator, an amplifier, a circulator, a second coupler, a balanced photoelectric detector, an analog-digital converter, a data processing and pulse control module, the discrete scattering enhanced optical fiber and an upper computer. Wherein the data processing and pulse control module is used for adaptively controlling the pulse interval and pulse width of probe light pulses output by the acousto-optic modulator and the number of light pulses with different pulse widths according to the distribution condition of enhanced scattering points in the discrete scattering enhanced optical fiber; the system is also used for realizing phase demodulation according to an input interference electric signal and uploading a demodulation result to an upper computer to complete positioning and restoration of a disturbance signal, can realize improvement of a sampling rate, can accurately and quickly distinguish and demodulate scattering signals of different detection light pulses, and is simple in scheme and high in practicability. And the method is suitable for application scenes with unequal scattering enhancement point intervals.

Description

Technical Field

[0001] The present invention belongs to the technical field of distributed optical fiber sensing, and in particular relates to an adaptive multi-pulse width pulse DAS method and system based on discrete scattering enhanced optical fiber. Background Art

[0002] Distributed Acoustic Sensing (DAS) technology is a type of fiber optic sensing technology. It can continuously monitor the vibration information of any position of the sensing fiber by using the information of Rayleigh scattered light from the fiber. It has the advantages of anti-electromagnetic interference, good concealment, corrosion resistance and insulation. At present, the DAS system mainly adopts the phase-sensitive optical time domain reflection technology, that is, the acoustic signal is restored by demodulating the phase change of the back Rayleigh scattered light. Due to the problems of interference fading, poor signal-to-noise ratio, sampling frequency limited by the fiber distance, and low sensitivity of ordinary single-mode fiber DAS technology, it is difficult to meet the needs of high-fidelity measurement of acoustic waves. Therefore, research and engineering applications related to scattering-enhanced fiber DAS technology have gradually received more attention. The DAS system using scattering-enhanced fiber has good coherent fading suppression effect and good signal-to-noise ratio, which has incomparable advantages over the traditional system based on ordinary single-mode fiber.

[0003] Although the sampling rate of the system based on scattering-enhanced optical fiber is also limited by the length of the sensing optical fiber, this limitation is not impossible to break through. When using point-type scattering-enhanced optical fiber to detect sound waves or vibration signals in some wide-range but relatively scattered areas, scattering enhancement points can be placed only in the area of ​​interest to achieve a balance between the detection range and the cost of optical cables. In this case, the sampling frequency is mainly improved through the method of time slot multiplexing, that is, inserting several identical pulses between adjacent detection light pulse intervals, and distinguishing the positions of different pulse detection peaks during demodulation. However, due to the consistent characteristics of all detection light pulses, the process of separating the scattering signals of different pulses is complicated, the phase demodulation speed is slow, and the demodulation consistency is not high. Especially for enhanced optical fibers with unequal scattering enhancement points, the accuracy of locating the scattering peaks of different pulses is low, and the scope of engineering application is not wide. In addition, pulses of different wavelengths can be inserted to improve the system sampling rate through wavelength division multiplexing, but such a method requires multiple light sources with different wavelengths, and wavelength division multiplexing and multi-channel detection are required at the receiving end, which will cause a significant increase in system costs. Summary of the invention

[0004] In view of the above, the purpose of the present invention is to provide an adaptive multi-pulse width pulse DAS method and system based on discrete scattering enhanced optical fiber, which can improve the system sampling rate while accurately and quickly distinguishing and demodulating the scattered signals of different detection light pulses. The solution is simple and suitable for application scenarios with unequal intervals between scattering enhancement points.

[0005] To achieve the above-mentioned purpose of the invention, an embodiment provides an adaptive multi-pulse width pulse DAS system based on discrete scattering enhanced optical fiber, comprising:

[0006] The system adopts a heterodyne coherent detection structure, including a narrow linewidth laser, a first coupler, an acousto-optic modulator, an amplifier, a circulator, a second coupler, a balanced photodetector, an analog-to-digital converter, a data processing and pulse control module, a discrete scattering enhanced optical fiber, and a host computer;

[0007] The narrow linewidth laser is used as a light source to output laser pulses, which are divided into detection light and local oscillator light by a first coupler. The detection light passes through an acousto-optic modulator and is modulated into detection light pulses under the control of a data processing and pulse control module and the acousto-optic modulator. The detection light is then sent to a discrete scattering enhanced optical fiber through an amplifier and a circulator. The backscattered light sent back by the discrete scattering enhanced optical fiber interferes with the local oscillator light after passing through the circulator. The interference optical signal is amplified by a balanced detector and converted into an interference electrical signal. The interference electrical signal is sampled by an analog-to-digital converter and sent to the data processing and pulse control module.

[0008] The data processing and pulse control module is used to adaptively control the pulse interval, pulse width and number of light pulses with different pulse widths of the detection light pulse output by the acousto-optic modulator according to the distribution of enhanced scattering points in the discrete scattering enhanced optical fiber; it is also used to realize phase demodulation according to the input interference electrical signal and upload the demodulation result to the host computer to complete the positioning and restoration of the disturbance signal.

[0009] Preferably, the detection light pulse output by the acousto-optic modulator is controlled to increase or decrease from an initial pulse width W in sequence within a period T, and the pulse width change step is ΔW, as a pulse group, wherein T=2nnL / c, c is the speed of light in a vacuum, L is the total length of the optical fiber, and n is the average refractive index of the optical fiber.

[0010] Preferably, in the data processing and pulse control module, the pulse interval, pulse width and number of light pulses with different pulse widths output by the acousto-optic modulator are adaptively controlled according to the distribution of enhanced scattering points in the discrete scattering enhanced optical fiber, including:

[0011] The distribution of enhanced scattering points is determined based on the backscattered light signal of the initial detection light pulse emitted by the acousto-optic modulator in the discrete scattering enhanced optical fiber. The distribution of enhanced scattering points includes: the minimum spacing d between adjacent scattering enhancement pointsmin , the maximum distance of the scattering enhancement area l max_1 and the minimum spacing between adjacent scattering enhancement regions l min _2;

[0012] Among them, d min Determine the pulse width range, the sampling rate f of the analog-to-digital converter determines the pulse width change step ΔW, d min , l max_1 , l min_2 , and f together determine the number of light pulses N with different pulse widths in the pulse group and the pulse interval between adjacent pulses.

[0013] Preferably, the sampling rate f of the analog-to-digital converter determines the pulse width change step ΔW, including: the pulse width change step ΔW and the sampling rate f satisfy: ΔW≥2 / f.

[0014] Preferably, d min Determine the pulse width range, including: Based on the minimum spacing d between adjacent scattering enhancement points min Determine the initial pulse width W should meet: Where c is the speed of light in vacuum, n is the average refractive index of the optical fiber, f is the sampling rate of the analog-to-digital converter, and N is the number of optical pulses with different pulse widths.

[0015] Preferably, d min , l max_1 , l min_2 , and f jointly determine the number of light pulses N with different pulse widths in the pulse group and the pulse interval between adjacent pulses. include:

[0016] When the length of each scattering enhancement region and the interval between adjacent scattering enhancement regions are different, the number of light pulses with different pulse widths Where W is the initial pulse width, c is the speed of light in a vacuum, n is the mean refractive index of the optical fiber, and floor means rounding down;

[0017] When the length of each scattering enhancement region l1 and the interval l2 between adjacent scattering enhancement regions are the same, the number of light pulses with different pulse widths

[0018] Adjacent pulse interval T is a period determined based on the total length of the optical fiber.

[0019] Preferably, when the length l1 of each scattering enhancement region and the interval l2 between adjacent scattering enhancement regions are the same, the backscattered light signal width Δt of different detection light pulses in the scattering enhancement region is l Keep the backscattered light signal interval Δt of different detection light pulses in adjacent scattering enhancement regions consistent i same.

[0020] Preferably, in the data processing and pulse control module, phase demodulation is implemented according to the input interference electrical signal, including:

[0021] The pulse envelope is restored according to the input interference electrical signal, and the position of the interference electrical signal is determined based on the pulse envelope, that is, a fixed window length data interception is performed on each interference electrical signal, and the window length must be less than the initial pulse width W. After the sampling point in each intercepted segment is phase demodulated, the difference is made with the fixed phase and the average is calculated to obtain the phase of the segment. Where k is the segment position corresponding to the phase;

[0022] Based on the pulse envelope, the pulse and enhanced scattering point where the interfering electrical signal comes from are determined, and the envelope information is sampled using an analog-to-digital converter. The number of sampling points for different widths will be different. The envelope width can be expressed as W+M·ΔW, M=0, 1,…, N-1. For a pulse envelope with a pulse width of W, the number of sampling points is floor(Wf), and the number of sampling points for a pulse envelope with a pulse width of W+ΔW is floor[(W+ΔW)f]. Then, floor(Wf) is used as the threshold for separating pulse envelopes with widths of W and W+ΔW, and floor[Wf+f(M-1)·ΔW] can be used as the threshold for separating pulse envelopes with widths of W+(M-1)·ΔW and W+M·ΔW. The distinguished pulse envelope is marked as Pi k , where i represents the pulse width group number, i is equal to M, i.e., the envelope corresponding to the pulse with a pulse width of W+M·ΔW, and k is the envelope count; since Pik and The k values ​​in correspondence are one-to-one. After screening, the phase information of the interference fragments of pulses with different pulse widths at any enhanced scattering point can be obtained. The phases of pulses with the same pulse width at adjacent interference fragments are selected for differential calculation and interleaved to obtain the time-varying strain information of the optical fiber when it is vibrated.

[0023] To achieve the above-mentioned purpose of the invention, an embodiment of the present invention provides an adaptive multi-pulse width pulse DAS method based on discrete scattering enhanced optical fiber, wherein the method adopts the above-mentioned adaptive multi-pulse width pulse DAS system and comprises the following steps:

[0024] The data processing and pulse control module controls the acousto-optic modulator to output an initial pulse, and determines the minimum spacing between adjacent scattering enhancement points, the maximum distance between scattering enhancement areas, and the minimum spacing between adjacent scattering enhancement areas according to the backscattering signal corresponding to the initial pulse. If it is not determined, the acousto-optic modulator is controlled to continuously output the initial pulse until it is determined.

[0025] After determination, the data processing and pulse control module adaptively calculates the pulse interval, pulse width and number of light pulses with different pulse widths of the detection light pulse, otherwise it returns to the previous step, controls the detection light pulse accordingly after the calculation is completed, and pulls up the indication signal. When the system detects that the indication signal is high, it performs phase demodulation processing.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention adopts an acousto-optic modulator to cyclically output detection light pulses with different pulse widths, so that the backscattered light signal shows inconsistency in peak width characteristics. For a heterodyne coherent detection structure, the interference signal envelope width will show inconsistency. Therefore, under the sampling of an analog-to-digital converter with a fixed sampling rate, the number of sampling points belonging to different pulses will show obvious differences. The position corresponding to any phase information can be accurately located by comparison and screening. The scheme is simple, the complexity of the demodulation process is low, and it does not occupy a large amount of logic resources in hardware implementation.

[0028] For the multi-pulse width pulse detection scheme, a method is proposed to process data based on the linear relationship between variables and the maximum value of the key variable, and calculate the appropriate number of pulses with different pulse widths, pulse width size and adjacent pulse intervals. The data is then fed back to the data processing and pulse control module to control the acousto-optic modulator to output the corresponding pulses. This makes the system independent of the specific distribution of enhanced optical fibers and has high adaptability in application scenarios where the distribution of enhanced scattering points is unknown. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 is a schematic structural diagram of an adaptive multi-pulse width pulse DAS system based on discrete scattering enhanced optical fiber provided in an embodiment;

[0031] Figure 2 is a schematic diagram of a discrete scattering enhanced optical fiber provided in an embodiment;

[0032] Figure 3 is a schematic diagram of a detection light pulse with a pulse width increasing successively within a period provided by an embodiment;

[0033] Figure 4 is a schematic diagram of a backscattered light signal of a multi-pulse width pulse provided in an embodiment;

[0034] Figure 5is a data processing flow chart of an adaptive multi-pulse width pulse DAS system based on discrete scattering enhanced optical fiber provided in an embodiment;

[0035] Figure 6 is a schematic diagram of an interference electrical signal with an envelope provided in an embodiment;

[0036] Figure 7 It is a multi-pulse width pulse system demodulation flow chart provided in an embodiment. DETAILED DESCRIPTION

[0037] To make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific implementation methods described herein are only used to explain the present invention and do not limit the scope of protection of the present invention.

[0038] Figure 1 Schematic diagram of an adaptive multi-pulse width DAS system based on discrete scattering enhanced fiber. Figure 1 As shown, the adaptive multi-pulse width pulse DAS system adopts a heterodyne coherent detection structure, including a narrow linewidth laser, a first coupler (i.e., coupler 1), an acousto-optic modulator, an amplifier (an erbium-doped fiber amplifier can be selected), a circulator, a second coupler (i.e., coupler 2), a balanced photodetector, an analog-to-digital converter (i.e., ADC), a data processing and pulse control module, a discrete scattering enhanced optical fiber, and a host computer.

[0039] A narrow linewidth laser is used as a light source to output laser pulses, which are divided into detection light (90%) and local oscillator light (10%) through a coupler 1. The detection light is pulse modulated by an acousto-optic modulator and amplified by an erbium-doped fiber amplifier, and then sent to a discrete scattering enhanced fiber through a circulator. When transmitted in the sensing fiber, it excites Rayleigh backscattered light, and the backscattered light returns with vibration sensing information. The backscattered light sent back by the discrete scattering enhanced fiber passes through the circulator and interferes with the local oscillator light in a coupler 2. After interference, the optical signal is amplified by a balanced detector and converted into an interference electrical signal. The ADC samples the interference electrical signal and sends it to a data processing and pulse control module. The data processing and pulse control module, on the one hand, controls the pulse interval, pulse width and number of pulses with different pulse widths of the optical pulse output by the acousto-optic modulator according to the distribution of enhanced scattering points of the enhanced optical fiber in the discrete scattering enhanced fiber, and on the other hand, realizes phase demodulation according to the input interference electrical signal and uploads the data to a host computer to complete the positioning and restoration of the disturbance signal.

[0040] In an embodiment, the discrete scattering enhanced optical fiber is as follows Figure 2As shown, the scattering enhancement points are distributed in regions, the total length of the optical fiber is L, the average refractive index of the optical fiber is n, the length of the scattering enhancement region is l1, and the interval between adjacent scattering enhancement regions is l2. The interval between adjacent enhanced scattering points in the same scattering enhancement region is d, and there are m1 scattering points in the scattering enhancement region, that is, l1 = (m1-1)·d.

[0041] In the embodiment, Figure 3 As shown, the detection light pulse output by the acousto-optic modulator is controlled to increase or decrease from the initial pulse width W in a period T, and the pulse width change step is ΔW, as a pulse group, where T = 2nL / c, c is the speed of light in a vacuum. The pulse width W±M·ΔW must be less than the time between the pulse and the nearest adjacent enhanced scattering point, that is, W±M·ΔW≤2nd min / c, where M ranges from 0, 1, ..., N-1, N is the number of light pulses with different pulse widths in a pulse group, d min is the minimum spacing between adjacent enhanced scattering points.

[0042] In the embodiment, the backscattered light signal of the multi-pulse width pulse is as follows: Figure 4 As shown in the figure, for the difference in pulse width of the pulses in the pulse group, the backscattered light signal will show inconsistency on the time axis, that is, the peak width W corresponding to the scattered light signal of the detection light pulse with different pulse widths F Using this difference, the scattered signals of different pulses can be quickly extracted to achieve phase demodulation, where the peak width is equal to the corresponding pulse width, that is, W F =W+M·ΔW.

[0043] If the length and interval of each scattering enhancement region are the same, the scattering signal width Δt of different detection light pulses in the scattering enhancement region is l Keep the scattering signal interval Δt of different detection light pulses in adjacent scattering enhancement regions consistent i The same, that is, Δt l =2nnl1 / c,Δt i =2n(l1+l2) / c.

[0044] In order to prevent the backscattered signals of different pulses from overlapping each other, the number of pulses with different pulse widths N in the pulse group must satisfy: N takes the largest positive integer solution, which is the maximum number of pulses with different pulse widths in the pulse group. Given that W+(N-1)·ΔW≤2nd min / c, to reduce the complexity of data processing, convert it into The largest positive integer solution for N is:

[0045] Adhering to the principle of equal intervals between the peak values ​​(center line) of the detection light pulses, the intervals between adjacent pulses are

[0046] The ADC sampling rate f (in GS / s) determines the size of the pulse width change step ΔW (in ns). The linear relationship between the two is ΔW ≥ 2 / f, that is, at a sampling rate of 1GS / s, ΔW ≥ 2ns must be satisfied, so the initial W must satisfy:

[0047] If the length and spacing of each scattering enhancement region are different, the maximum value of l1 should be taken. max_1 and the minimum value l of l2 min _2 is calculated to ensure that different pulse scattering signals do not overlap each other, that is,

[0048] In summary, in the system, the minimum spacing d between adjacent enhanced scattering points is min The ADC sampling rate f determines the pulse width range, that is, the pulse width change step ΔW, and the maximum distance l between the two and the enhanced scattering area max _1 and the minimum spacing between adjacent scattering enhancement regions l min _2 jointly determine the number of pulses with different pulse widths in the pulse group and the size of the interval between adjacent pulses. Therefore, the linear relationship between these variables can be used to adaptively adjust the number of pulses with different pulse widths, pulse width size and pulse interval for enhanced optical fibers with unknown distribution of scattering enhancement points.

[0049] Based on the above system, the embodiment also provides an adaptive multi-pulse width pulse DAS method based on discrete scattering enhanced fiber, such as Figure 5 As shown, it includes the following steps:

[0050] The data processing and pulse control module controls the acousto-optic modulator to output an initial pulse, and determines the minimum spacing between adjacent scattering enhancement points, the maximum distance between scattering enhancement areas, and the minimum spacing between adjacent scattering enhancement areas according to the backscattering signal corresponding to the initial pulse. If it is not determined, the acousto-optic modulator is controlled to continuously output the initial pulse until it is determined.

[0051] After determination, the data processing and pulse control module adaptively calculates the pulse interval, pulse width and number of light pulses with different pulse widths of the detection light pulse, otherwise it returns to the previous step, and after the calculation is completed, it controls the detection light pulse accordingly and pulls up the indication signal control. When the system detects that the indication signal is high, that is, control=1, phase demodulation processing is performed.

[0052] Figure 6The figure is a schematic diagram of an interference electrical signal with an envelope. During demodulation, the scattered signals of the same detection light pulse at adjacent enhanced scattering points are selected and signal segments of the same length are intercepted for demodulation processing. The system adopts a heterodyne coherent detection structure, and the balanced photodetector outputs an interference signal with a pulse envelope, and the envelope width is equal to the corresponding pulse width.

[0053] Figure 7 This is a demodulation flow chart for a multi-pulse width pulse system. For a multi-pulse width pulse system, it is necessary to accurately distinguish the detection light pulse and its enhanced scattering point position from which the interference electrical signal in each envelope comes during demodulation. Since the interval between adjacent detection light pulses is much longer than the time it takes for the detection light pulse to go back and forth in the adjacent enhanced scattering area, the scattered light signals in the same group will come from different scattering areas, making it impossible to distinguish the demodulated phase information using regularity.

[0054] Therefore, the phase demodulation of multi-pulse width pulses is carried out, and the specific process is as follows:

[0055] After the ADC converts the interference signal into a digital signal, the pulse envelope must be restored first. After the pulse envelope is restored, the position of the interference signal can be determined, and a fixed window length data interception is performed on each interference signal (the window length must be less than the initial pulse width W of the pulse). After the sampling point in each segment is phase demodulated, the difference is made with the fixed phase and the average is calculated to obtain the phase of the segment. Where k is the segment position corresponding to the phase. On the other hand, it is necessary to determine which pulse and which enhanced scattering point the interference signal comes from based on the envelope width.

[0056] When using ADC to sample the envelope information, the number of sampling points for different widths will be different. For a pulse envelope with a width of W, the number of ADC sampling points is floor(Wf), and the number of sampling points for a pulse envelope with a width of W+ΔW is floor[(W+ΔW)f]. Then floor(Wf) is used as the threshold for separating pulse envelopes with widths of W and W+ΔW, and floor[Wf+f(M-1)·ΔW] can be used as the threshold for separating pulse envelopes with widths of W+(M-1)·ΔW and W+M·ΔW.

[0057] Mark the distinguished envelope as P ik , where i is the pulse width group number, i is equal to M, i.e. the envelope corresponding to the pulse with a pulse width of W+M·ΔW, and k is the envelope count. ik and The k values ​​in the image correspond one to one. After screening, the phase information of the interference fragments of pulses with different pulse widths at any enhanced scattering point can be obtained. The phases of pulses with the same pulse width at adjacent interference fragments are selected for differential calculation and interleaved to obtain the time-varying strain information of the optical fiber when it is vibrated.

[0058] The specific implementation methods described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An adaptive multi-pulse width pulse DAS system based on discrete scattering enhanced fiber, characterized in that: The system adopts a heterodyne coherent detection structure, including a narrow linewidth laser, a first coupler, an acousto-optic modulator, an amplifier, a circulator, a second coupler, a balanced photodetector, an analog-to-digital converter, a data processing and pulse control module, a discrete scattering enhanced optical fiber, and a host computer; The narrow linewidth laser is used as a light source to output laser pulses, which are divided into detection light and local oscillator light by a first coupler. The detection light passes through an acousto-optic modulator and is modulated into detection light pulses under the control of a data processing and pulse control module and the acousto-optic modulator. The detection light is then sent to a discrete scattering enhanced optical fiber through an amplifier and a circulator. The backscattered light sent back by the discrete scattering enhanced optical fiber interferes with the local oscillator light after passing through the circulator. The interference optical signal is amplified by a balanced detector and converted into an interference electrical signal. The interference electrical signal is sampled by an analog-to-digital converter and sent to the data processing and pulse control module. The data processing and pulse control module is used to adaptively control the pulse interval, pulse width and number of light pulses with different pulse widths of the detection light pulse output by the acousto-optic modulator according to the distribution of enhanced scattering points in the discrete scattering enhanced optical fiber; it is also used to realize phase demodulation according to the input interference electrical signal and upload the demodulation result to the host computer to complete the positioning and restoration of the disturbance signal.

2. The adaptive multi-pulse width pulse DAS system based on discrete scattering enhanced fiber according to claim 1, characterized in that: The detection light pulse output by the acousto-optic modulator is controlled to increase or decrease in sequence from an initial pulse width W within a period T, and the pulse width change step is ΔW, as a pulse group, wherein T=2nL / c, c is the speed of light in vacuum, L is the total length of the optical fiber, and n is the average refractive index of the optical fiber.

3. The adaptive multi-pulse width pulse DAS system based on discrete scattering enhanced fiber according to claim 1 or 2, characterized in that: In the data processing and pulse control module, the pulse interval, pulse width and number of light pulses with different pulse widths output by the acousto-optic modulator are adaptively controlled according to the distribution of enhanced scattering points in the discrete scattering enhanced optical fiber, including: The distribution of enhanced scattering points is determined based on the backscattered light signal of the initial detection light pulse emitted by the acousto-optic modulator in the discrete scattering enhanced optical fiber. The distribution of enhanced scattering points includes: the minimum spacing d between adjacent scattering enhancement points min , the maximum distance of the scattering enhancement area l max_1 and the minimum spacing between adjacent scattering enhancement regions l min_2 ; Among them, d min Determines the pulse width range, the sampling rate f of the analog-to-digital converter determines the pulse width change step ΔW, d min , l max_1 , l min_2 , and f together determine the number of light pulses N with different pulse widths in the pulse group and the pulse interval between adjacent pulses.

4. The adaptive multi-pulse width pulse DAS system based on discrete scattering enhanced fiber according to claim 3, characterized in that: The sampling rate f of the analog-to-digital converter determines the pulse width change step ΔW, including: the pulse width change step ΔW and the sampling rate f satisfy: ΔW≥2 / f.

5. The adaptive multi-pulse width pulse DAS system based on discrete scattering enhanced fiber according to claim 3, characterized in that: d min Determine the pulse width range, including: Based on the minimum spacing d between adjacent scattering enhancement points min Determine the initial pulse width W should meet: Where c is the speed of light in vacuum, n is the average refractive index of the optical fiber, f is the sampling rate of the analog-to-digital converter, and N is the number of optical pulses with different pulse widths.

6. The adaptive multi-pulse width pulse DAS system based on discrete scattering enhanced fiber according to claim 3 or 5, characterized in that: d min , l max_1 , l min_2 , and f jointly determine the number of light pulses N with different pulse widths in the pulse group and the pulse interval between adjacent pulses. include: When the length of each scattering enhancement region and the interval between adjacent scattering enhancement regions are different, the number of light pulses with different pulse widths Where W is the initial pulse width, c is the speed of light in a vacuum, n is the mean refractive index of the optical fiber, and floor means rounding down; When the length of each scattering enhancement region l1 and the interval between adjacent scattering enhancement regions l2 are the same, the number of light pulses with different pulse widths Adjacent pulse interval T is a period determined based on the total length of the optical fiber.

7. The adaptive multi-pulse width pulse DAS system based on discrete scattering enhanced fiber according to claim 6, characterized in that: When the length of each scattering enhancement region l1 and the interval l2 between adjacent scattering enhancement regions are the same, the backscattered light signal width Δt of different detection light pulses in the scattering enhancement region l Keep the backscattered light signal interval Δt of different detection light pulses in adjacent scattering enhancement regions consistent i same.

8. The adaptive multi-pulse width pulse DAS system based on discrete scattering enhanced fiber according to claim 1, characterized in that: In the data processing and pulse control module, phase demodulation is implemented according to the input interference electrical signal, including: The pulse envelope is restored according to the input interference electrical signal, and the position of the interference electrical signal is determined based on the pulse envelope, that is, a fixed window length data interception is performed on each interference electrical signal, and the window length must be less than the initial pulse width W. After the sampling point in each intercepted segment is phase demodulated, the difference is made with the fixed phase and the average is calculated to obtain the phase of the segment. Where k is the segment position corresponding to the phase; Based on the pulse envelope, the pulse and enhanced scattering point from which the interfering electrical signal comes are determined, and the envelope information is sampled using an analog-to-digital converter. The number of sampling points for different widths will be different; the envelope pulse width is expressed as W+M·ΔW, M=0,1,…,N-1, the number of sampling points for the pulse envelope with a pulse width of W is floor(Wf), and the number of sampling points for the pulse envelope with a pulse width of W+ΔW is floor[(W+ΔW)f]. Then, floor(Wf) is used as the threshold for separating the pulse envelopes with widths of W and W+ΔW, and floor[Wf+f(M-1)·ΔW] can be used as the threshold for separating the pulse envelopes with widths of W+(M-1)·ΔW and W+M·ΔW; the distinguished pulse envelope is marked as P ik , where i represents the pulse width group number, i is equal to M, i.e., the envelope corresponding to the pulse with a pulse width of W+M·ΔW, and k is the envelope count; since P ik and The k values ​​in correspondence are one-to-one. After screening, the phase information of the interference fragments of pulses with different pulse widths at any enhanced scattering point can be obtained. The phases of pulses with the same pulse width at adjacent interference fragments are selected for differential calculation and interleaved to obtain the time-varying strain information of the optical fiber when it is vibrated.

9. An adaptive multi-pulse width pulse DAS method based on discrete scattering enhanced fiber, characterized in that: The method adopts the adaptive multi-pulse width pulse DAS system according to any one of claims 1 to 8, comprising the following steps: The data processing and pulse control module controls the acousto-optic modulator to output an initial pulse, and determines the minimum spacing between adjacent scattering enhancement points, the maximum distance between scattering enhancement areas, and the minimum spacing between adjacent scattering enhancement areas according to the backscattering signal corresponding to the initial pulse. If it is not determined, the acousto-optic modulator is controlled to continuously output the initial pulse until it is determined. After determination, the data processing and pulse control module adaptively calculates the pulse interval, pulse width and number of light pulses with different pulse widths of the detection light pulse, otherwise it returns to the previous step, controls the detection light pulse accordingly after the calculation is completed, and pulls up the indication signal. When the system detects that the indication signal is high, it performs phase demodulation processing.

10. The method for adaptive multi-pulse width DAS based on discrete scattering enhanced fiber according to claim 9, characterized in that: The phase demodulation process includes: The pulse envelope is restored according to the input interference electrical signal, and the position of the interference electrical signal is determined based on the pulse envelope, that is, a fixed window length data interception is performed on each interference electrical signal, and the window length must be less than the initial pulse width W. After the sampling point in each intercepted segment is phase demodulated, the difference is made with the fixed phase and the average is calculated to obtain the phase of the segment. Where k is the segment position corresponding to the phase; Based on the pulse envelope, the pulse and enhanced scattering point where the interfering electrical signal comes from are determined, and the envelope information is sampled using an analog-to-digital converter. The number of sampling points for different widths will be different; the envelope width is expressed as W+M·ΔW, M=0,1,…,N-1; for a pulse envelope with a pulse width of W, the number of sampling points is floor(Wf), and the number of sampling points for a pulse envelope with a pulse width of W+ΔW is floor[(W+ΔW)f]. Then, floor(Wf) is used as the threshold for separating pulse envelopes with widths of W and W+ΔW, and floor[Wf+f(M-1)·ΔW] can be used as the threshold for separating pulse envelopes with widths of W+(M-1)·ΔW and W+M·ΔW. The distinguished pulse envelope is marked as P ik , where i represents the pulse width group number, i is equal to M, i.e., the envelope corresponding to the pulse with a pulse width of W+M·ΔW, and k is the envelope count; since P ik and The k values ​​in correspondence are one-to-one. After screening, the phase information of the interference fragments of pulses with different pulse widths at any enhanced scattering point can be obtained. The phases of pulses with the same pulse width at adjacent interference fragments are selected for differential calculation and interleaved to obtain the time-varying strain information of the optical fiber when it is vibrated.

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