Phase extraction method of external disturbance events based on local spatial data

Abstract

The present invention discloses a method for extracting the phase of an external disturbance event based on local spatial data. The method first adjusts the trigger delay of a synchronous trigger pulse according to the optical fiber position of interest to the collector, changing the starting point of optical fiber sampling so that the acquisition end delays for a period of time after capturing each synchronous trigger pulse before starting to collect a certain amount of local spatial data. This ensures that each synchronous trigger is effective, saves data storage space, and reduces the system's computational burden. An optimized phase unwrapping algorithm is then used to perform phase unwrapping on the local spatial data. The optimized phase unwrapping algorithm does not require phase information from the optical fiber injection end. When the differential position is the same, the results are consistent with those of a traditional phase unwrapping algorithm, while optimizing the algorithm processing process and reducing data processing time. The present invention combines local spatial data with the optimized phase unwrapping algorithm to effectively reduce the amount of data, shorten the time required for data processing, and ensure real-time system monitoring.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to a method for extracting the phase of an external disturbance event based on local spatial data. Background Art

[0002] Phase-Sensitive Optical Time Domain Reflectometry Using optical fiber as a sensing medium to detect external disturbances has the characteristics of high sensitivity and wide monitoring range, and is widely used in perimeter security monitoring, seabed exploration, oil and gas pipeline monitoring and other fields. (like Figure 1 As shown in the figure, the laser light emitted by the laser is divided into 90% detection light and 10% reference light by the coupler. After the 90% detection light is modulated into pulse light by the acousto-optic modulator, it enters the sensing fiber through a circulator and collides with the scattering particles in the fiber, generating a continuous and random backscattered Rayleigh scattering signal (the backscattered Rayleigh scattering signal contains the disturbance information generated by the external disturbance event). The backscattered Rayleigh scattering signal is transmitted back through the circulator, coupled with the 10% reference light and split into two parts to enter the balanced detector. After being processed by the balanced detector, the intermediate frequency signal is obtained. The intermediate frequency signal is collected by the acquisition card and sent to the host computer. The host computer performs orthogonal (IQ) demodulation on the intermediate frequency signal and calculates the amplitude and phase of the demodulated intermediate frequency signal to realize the analysis of the external disturbance event. The pulse signal emitted by the signal generator serves as the modulation pulse of the acousto-optic modulator on the one hand and the synchronization trigger pulse of the acquisition card on the other hand.

[0003] current The acquisition method used is that after the acquisition card captures the first synchronous trigger pulse sent by the signal generator, it continuously acquires all the intermediate frequency signals under all subsequent modulated pulses and no longer pays attention to the subsequent synchronous trigger pulses. Traditional data acquisition requires that the intermediate frequency data under all pulse periods be acquired and demodulated (demodulation obtains amplitude and phase), and the pulse period of the modulated pulse is required to be greater than the single round-trip time of light in the sensing optical fiber in the initial setting to ensure that two consecutive pulses of light do not meet in the optical fiber. This approach undoubtedly increases the actual acquisition "fiber length" and is much greater than the length of the measured optical fiber. It also means that the added acquisition points behind the measured optical fiber are invalid, resulting in a large amount of data acquisition and an increased system burden during data processing. In addition, since the phase of the external disturbance event is wrapped in (-π,π) after demodulation, it cannot reflect the linear relationship with the external disturbance, so it also needs to be phase unfolded. However, the current The traditional phase unwrapping algorithm must include four steps: spatial difference, unwrapping along the spatial direction, unwrapping along the temporal direction, and temporal difference. Among them, unwrapping along the spatial direction requires processing the phase of all positions on the measured optical fiber to ensure the continuity of phase unwrapping, which increases the calculation burden of the system and reduces the efficiency of obtaining phase information. For this reason, in real-time online monitoring, In the process of external disturbance, amplitude information is usually used to describe the external disturbance event, while the phase information of the external disturbance event is more likely to be obtained by saving the intermediate frequency data or IQ data and then performing offline processing. Summary of the Invention

[0004] The present invention is to solve the current The traditional data acquisition method and traditional phase unwrapping method used have problems such as large data volume, great processing difficulty, long time and low timeliness. This paper provides a phase extraction method for external disturbance events based on local spatial data.

[0005] To solve the above problems, the present invention is achieved through the following technical solutions:

[0006] The method for extracting the phase of an external disturbance event based on local spatial data includes the following steps:

[0007] Step 1: Determine the fiber segments L1 to L2 that require current attention.

[0008] Step 2: Determine the fiber segment L1 to L2 that needs attention. The local spatial position to be collected is L1-l1 to L2+l2;

[0009] Step 3: According to the determined local space position, set The trigger delay τ of the synchronous trigger pulse and the data record length RL after the trigger delay;

[0010] The trigger delay τ is:

[0011] τ=t ′ ×(L1-l1)

[0012] The data record length RL is:

[0013] RL≥(L2-L1+l1+l2)×t ′ ×f

[0014] Step 4: Collect the intermediate frequency data under n consecutive synchronous trigger pulses, that is, when the trigger edge of each synchronous trigger pulse arrives, start collecting intermediate frequency data of length RL after a delay of τ, thereby obtaining a local spatial intermediate frequency data matrix IF of size n×RL;

[0015] Step 5: Perform orthogonal demodulation on the local spatial intermediate frequency data matrix IF to obtain the initial phase matrix θ;

[0016] Step 6: Use the optimized phase unwrapping algorithm to unwrap the initial phase matrix θ, restore the true value of the phase, and obtain the true phase matrix Θ; that is:

[0017] Step 6.1: Perform spatial difference operation on the initial phase matrix θ to obtain the spatial difference matrix θ 1 ;

[0018] Step 6.2: Spatial difference matrix θ 1 Perform phase unwrapping along the time direction to obtain the unwrapped phase matrix θ 2 ;

[0019] Step 6.3: The phase matrix θ after unwrapping 2 Perform time difference operation to obtain the real phase matrix Θ;

[0020] Step 7: Extract the phase of the external disturbance event based on the real phase matrix Θ, that is, the phase of any position in the stable region after the end point L2 of the optical fiber segment currently in focus in the real phase matrix Θ;

[0021] The above L1 is the starting point of the fiber segment that needs to be paid attention to, and L2 is the end point of the fiber segment that needs to be paid attention to; l1 is the pre-reserved fiber length of the fiber segment that needs to be paid attention to, and l2 is the post-reserved fiber length of the fiber segment that needs to be paid attention to, l1≥SR, l2≥SR, SR is The spatial resolution of t ′ is the time required for light to travel 1 meter in the optical fiber; f is The sampling frequency is τ, the trigger delay is RL, and the number of pulses is n.

[0022] In the above step 1, the optical fiber segments L1 to L2 that currently require attention are determined by a manual designation method or an adaptive method.

[0023] The specific process of using the adaptive method to determine the fiber segments L1 to L2 that need attention is as follows: First, the intermediate frequency signals within a certain period of time after a trigger pulse are collected using a traditional data acquisition method; then, these intermediate frequency signals are demodulated and divided according to the sampling points under a single modulation pulse to obtain a time-space matrix containing the intermediate frequency signal amplitudes of M×N sampling points, where M is the number of data frames and N is the period T of a single modulation pulse. pulse Finally, the differential accumulation algorithm is used to locate the fiber segment range where the disturbance roughly occurs on the spatiotemporal matrix of the intermediate frequency signal amplitude, and the fiber segment range where the disturbance roughly occurs is taken as the fiber segment L1~L2 that needs attention.

[0024] In step 2 above, the spatial resolution SR is:

[0025]

[0026] Where c is the speed of light in vacuum, w is The modulation pulse width of the acousto-optic modulator, n eff is the refractive index of the sensing fiber core.

[0027] In step 3 above, the sampling frequency f is:

[0028]

[0029] Where f0 is The frequency shift of the acousto-optic modulator is: B is the bandwidth of the intermediate frequency signal, m is an integer, 1≤m≤j, j is The integer part of .

[0030] Compared with the prior art, the present invention has the following characteristics:

[0031] 1. The present invention adjusts the trigger delay of the synchronous trigger pulse according to the optical fiber position of interest to the collector, changes the starting point of optical fiber sampling, and makes the acquisition end delay for a period of time after capturing each synchronous trigger pulse before starting to collect certain spatial data (i.e., local spatial data). This ensures that each synchronous trigger is effective, saves data storage space, and reduces the system's computing burden.

[0032] 2. The present invention uses an optimized phase unwrapping algorithm (spatial difference, unwrapping along the time direction, and time difference) to perform phase unwrapping on local spatial data. The optimized phase unwrapping algorithm does not require phase information at the fiber injection end, nor does it require unwrapping along the spatial direction. When the differential position is the same, the results are consistent with those of the traditional phase unwrapping algorithm. The optimized algorithm significantly reduces data processing time.

[0033] 3. The present invention combines local spatial data with an optimized phase unwrapping algorithm, which can effectively reduce the amount of data, shorten the time required for data processing, and ensure the real-time performance of system monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 for Schematic diagram.

[0035] Figure 2 Schematic diagram of the phase extraction method of external disturbance events based on local spatial data.

[0036] Figure 3 This is the waveform phase recovery diagram of Experiment 1.

[0037] Figure 4 Waveform phase recovery diagram of Experiment 2, (a) phase change caused by disturbance 1, (b) phase change caused by all disturbances, (c) phase change caused by disturbance 2. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific examples.

[0039] A phase extraction method for external disturbance events based on local spatial data, such as Figure 2 As shown, the specific steps include:

[0040] Step 1: Determine the optical fiber segments L1 to L2 that currently require attention, where L1 is the starting point of the optical fiber segment that currently requires attention, and L2 is the ending point of the optical fiber segment that currently requires attention.

[0041] The fiber segments L1~L2 that currently require attention can be determined manually or adaptively. When the fiber segments L1~L2 that require attention are determined manually, the fiber segments L1~L2 are fixed values. When the fiber segments L1~L2 that require attention are determined adaptively, the fiber segments L1~L2 are variable values. The specific process of using an adaptive method to determine the fiber segments L1~L2 that require attention is as follows: first, use a traditional data acquisition method to collect the intermediate frequency signal within a certain period of time after a trigger pulse; then demodulate these intermediate frequency signals and divide them according to the sampling points under a single modulation pulse to obtain a time-space matrix containing the intermediate frequency signal amplitudes of M×N sampling points, where M is the number of data frames and N is the period T of a single modulation pulse. pulse The number of sampling points under the condition is set; then the differential accumulation algorithm is used to locate the fiber segment range where the disturbance roughly occurs on the spatiotemporal matrix of the intermediate frequency signal amplitude, and the fiber segment range where the disturbance roughly occurs is taken as the fiber segment L1~L2 that needs attention.

[0042] Step 2: Determine the fiber segment L1 to L2 that needs attention. The local spatial position to be collected is L1-l1~L2+l2, where l1 is the pre-reserved fiber length of the fiber segment currently in need of attention, l2 is the post-reserved fiber length of the fiber segment currently in need of attention, and l1≥SR, l2≥SR, SR is spatial resolution.

[0043] The spatial resolution SR is:

[0044]

[0045] Where c is the speed of light in vacuum, w is The modulation pulse width of the acousto-optic modulator, n eff is the refractive index of the sensing fiber core.

[0046] Step 3: According to the determined local spatial position, set the trigger delay τ of the synchronous trigger pulse and the data record length RL after the trigger delay.

[0047] By setting the trigger delay τ of the synchronous trigger pulse, the starting position of the local spatial data acquisition is L1-l1. The trigger delay τ set accordingly needs to satisfy the following relationship:

[0048] τ=t ′ ×(L1-l1)

[0049] Among them, t ′ is the time required for light to travel 1 meter in the optical fiber, L1 is the starting point of the optical fiber segment currently in need of attention, and l1 is the length of the optical fiber reserved in front of the optical fiber segment currently in need of attention.

[0050] By setting the data record length RL after the trigger delay, the data length of the local space data acquisition is equal to the number of optical fiber sampling points within the local space position L1-l1 to L2+l2. The data record length RL set accordingly needs to satisfy the following relationship:

[0051] RL≥(L2-L1+l1+l2)×t ′ ×f

[0052] Among them, L2 is the end point of the fiber segment that needs attention, L1 is the starting point of the fiber segment that needs attention, l1 is the front reserved fiber length of the fiber segment that needs attention, l2 is the rear reserved fiber length of the fiber segment that needs attention, t ′ is the time required for light to travel 1 meter in the optical fiber, and f is The sampling frequency, sampling frequency f, is calculated by combining the bandpass sampling theorem:

[0053]

[0054] Where f0 is The frequency shift of the acousto-optic modulator is: The integer and fractional parts of .

[0055] Step 4: Collect intermediate frequency data under n consecutive synchronous trigger pulses to obtain a local spatial intermediate frequency data matrix IF of size n×RL; where n is the set number of pulses.

[0056] The acquisition method of the intermediate frequency data under each synchronous trigger pulse is: when the trigger edge of each synchronous trigger pulse arrives, the intermediate frequency data with a length of RL is acquired after a delay of τ.

[0057] Step 5: Perform orthogonal demodulation on the local spatial intermediate frequency data matrix IF to obtain the initial phase matrix θ.

[0058] The element θ(t i , z j ) represents the i-th sampling time t i The next j-th actual optical fiber sampling point z j The initial phase at (starting from the local spatial position), where t i ∈[1, n], n is the number of pulses; z j ∈[1,RL], RL is the record length.

[0059] Step 6: Use the optimized phase unwrapping algorithm to perform phase unwrapping on the initial phase matrix θ, restore the true value of the phase, and obtain the true phase matrix Θ.

[0060] The optimized phase unwrapping algorithm is derived from the definition of phase unwrapping. Phase unwrapping is defined as: when the phase jump between two consecutive phases θ1 and θ2 is greater than |π|, k 2π are added to the subsequent phase θ2 to make the jump less than |π|. It can be expressed as:

[0061] |θ2+2kπ-θ1|<π

[0062] Wherein, k is an integer.

[0063] Based on the definition of phase unwrapping, we can deduce its three properties: ① uniqueness of k: for two phases in a specific order, k exists and is unique; ② followability of k: when the current phase θ1 increases by 2k1π, the subsequent phase θ2 increases by 2kπ and then by another 2k1π, following the change of the previous phase θ1, where k1 is an integer; ③ constant invariance of k: for two phases in a specific order, increasing or decreasing the constant C at the same time does not affect the jump.

[0064] Based on the three properties of phase unwrapping, this invention optimizes the phase unwrapping algorithm. Considering that the main dispute between the optimized phase unwrapping algorithm and the traditional phase unwrapping algorithm is the necessity of two phase unwrapping operations, this paper directly performs phase unwrapping on any random matrix along its row vectors and column vectors, simulating the phase unwrapping of the differential phase matrix along the spatial and temporal directions, and observing the changes brought about by the two phase unwrapping operations on the random matrix.

[0065] For a matrix θ of shape M×N:

[0066]

[0067] Perform the first phase unwrapping along the row vector, that is, perform spatial unwrapping along the length of the optical fiber, and obtain the unwrapping matrix θ 1 , where the unwrapping matrix θ 1 The element θ in the mth row and nth column 1 (m,n) is:

[0068]

[0069] |θ 1 (m,n)-θ 1 (m,n-1)|<π

[0070] Where, is an integer, is the phase change produced by the mth row and nth column of the matrix θ after unwrapping along the row vector.

[0071] Before performing phase unwrapping along the column direction, we first observe the effect of the unwrapping operation on the phase value of each position. According to the uniqueness of unwrapping, we can conclude that:

[0072] |θ(m,n)+2h mn π-θ(m,n-1)|<π

[0073] Where h mn is an integer, h m1 =0,2h mn π is the phase jump between the mth row and the nth column and the n-1th column in θ.

[0074] According to the property ② (followability), the unwinding matrix θ 1 in Rewrite:

[0075]

[0076] It can be seen that the phase change after each row vector is unwrapped is They are all obtained by adding up the phase jump values ​​of the first n columns of the mth row. That is, the phase unwrapping along any direction has a unique and additive effect on the phase of a certain point (for data in a fixed order, its phase jump value is unique and additive). This property is independent of the direction (row / column, space / time) and is only related to the phase unwrapping itself. Specifically:

[0077]

[0078] in, is θ 1 The mth row of

[0079]

[0080] According to the uniqueness and superposition of phase jump values, it can be deduced that the matrix θ 1 Unwrap along the column vector, for θ 1 Any point θ 1 (m,n), its phase jump value only depends on the phase of the first m rows of the nth column. At this time, the effect of row vector unwrapping on phase expansion only retains the first row of row vector unwrapping. For other row vectors, the phase change caused by row vector unwrapping is reset due to the uniqueness of the jump when the column vector is unwrapped; and the followability determines that the phase at the nth position of each subsequent row must contain a constant value. θ 1 Unwrapping along the column vector is specifically expressed as:

[0081]

[0082] θ 2 is the matrix θ 1 The matrix after unwrapping along the column vector, where:

[0083]

[0084] in, is θ 2 The nth column, c mn is an integer, c 1n =0,2c mn π is the phase change at adjacent moments in the same position in the random matrix θ[M,N], that is:

[0085] |θ(m,n)+2c mn π-θ(m-1,n)|<π

[0086] Observe the matrix θ after the phase unwrapping of row vectors and column vectors 2 The difference between [M,N] and the original matrix θ only retains the effects of column vector unwrapping and row vector unwrapping along the first row of the matrix θ. However, in order to eliminate system noise, the overall phase unwrapping algorithm also includes time difference, that is, the phase at each spatial position is subtracted from the phase mean of the position over time. In terms of the mean, After time difference, it is directly eliminated It can be seen that the effect of row vector unwrapping on phase unwrapping is completely eliminated after mean subtraction. In other words, spatial phase unwrapping is ineffective in traditional phase unwrapping algorithms, which can be used to optimize the phase unwrapping algorithm. Therefore, the optimized phase unwrapping algorithm proposed in this invention specifically includes the following steps:

[0087] Step 6.1: Perform spatial difference operation on the initial phase matrix θ to obtain the spatial difference matrix θ 1 . Spatial difference matrix θ 1 The element θ in the i-th row and j-th column of 1 (t i , z j )for:

[0088] θ 1 (t i , z j )=θ(t i , z j )-θ(t i , z s )

[0089] Among them, θ(t i , z j ) represents the element of the i-th row and j-th column of the initial phase matrix θ; θ(t i , z s ) represents the element of the i-th row and s-th column of the initial phase matrix θ, where s is the specified column, z s is the reference point of the initial phase, z s ∈[1,l1×t ′ ×f], l1 is the pre-reserved fiber length of the fiber segment that needs attention, t ′ is the time required for light to travel 1 meter in the optical fiber, f is the sampling frequency, z s The closer to the disturbance location, the better the phase noise suppression effect.

[0090] Step 6.2: Spatial difference matrix θ 1 Perform phase unwrapping along the time direction to obtain the unwrapped phase matrix θ 2 .

[0091] The phase matrix θ after unwrapping 2 The element θ in the i-th row and j-th column of 2 (t i , z j )for:

[0092] θ 2 (t i , z j )=θ 1 (t i , z j )+2k ij π

[0093] Among them, θ 1 (t i , z j ) represents the spatial difference matrix θ1 The element in row i and column j of ij π represents θ 1 (t i , z j ) and θ 2 (t i-1 , z j ), k ij The value of needs to make the phase matrix θ after unwrapping 2 The following conditions are met:

[0094] |θ 2 (t i , z j )-θ 2 (t i-1 , z j )|<π

[0095] Among them, k 1j =0, that is, θ 2 (t1, z j )=θ 1 (t1, z j ).

[0096] Step 6.3: The phase matrix θ after unwrapping 2 Perform time difference operation to obtain the true phase matrix Θ.

[0097] The element Θ(t i , z j )for:

[0098]

[0099] Among them, θ 2 (t i , z j ) represents the phase matrix θ after unwrapping 2 The element in the i-th row and j-th column of , where n is the number of pulses.

[0100] Step 7: Extract the phase of the external disturbance event based on the true phase matrix Θ.

[0101] The phase of the extracted external disturbance event is the phase of any position in the stable region after the end point L2 of the fiber segment that needs to be paid attention to in the real phase matrix Θ, that is, Θ(t i , z phi ), where z phi ∈[(L2+l2)×t ′ ×f+1,RL)].

[0102] The following uses Figure 1 The coherent detection structure shown As an experimental device, the frequency shift of the acousto-optic modulator is 80MHz, and the pulse width is adjusted to 100ns. The data acquisition system can adjust the trigger delay and the acquisition length of a single trigger, and can also adjust the sampling frequency. The schematic diagram of the local space data acquisition is as follows Figure 2 As shown, the approximate location of the disturbance is determined first, and then local spatial data is collected. Figure 2 In the figure, the horizontal axis is the fiber length in meters (m), which can also be converted into the round-trip time of a single pulse in seconds (s); the vertical axis is the number of pulses, which is proportional to the disturbance time. pulse It is set according to the fiber length L; the trigger delay τ and the record length RL are set according to the disturbance position (L1~L2); the number of pulses n is set according to the time T of the acquisition event.

[0103] Example 1: Experiment on 1.2 km optical fiber, setting the pulse period T pulse Should be greater than the round trip time T of light in the optical fiber L =12μs, in order to ensure that the time of collecting disturbance is long enough, the pulse period is set to T pulse = 100μs; use a piezoelectric ceramic (PZT) of about 50m as disturbance 1, assume that the range of the known disturbance is 525m~575m, set the sampling frequency f=200MSa / s, the local spatial position is 450m~650m, the trigger delay τ=450ns, and the record length RL=400. The phase of the disturbance signal recovered by the present invention is as follows Figure 3 As shown in the figure, the horizontal axis represents the time T of the acquisition event; the vertical axis represents the phase value of the disturbance. pulse =100μs The actual sampleable fiber length is L ′ = 10 km, while local spatial data requires data collected over 200 m of fiber to successfully recover the phase of the disturbance signal. Therefore, when collecting disturbance events of the same time T at the same sampling frequency, the traditional method collects 50 times the amount of data as the local spatial data acquisition method, i.e., k = 50.

[0104] Note: Set T pulse >T L The purpose is to reduce the number of pulse acquisitions under the same disturbance time. If strictly according to T pulse =T L In this example, k=6. In actual applications, it is necessary to set it reasonably according to the disturbance frequency collected. pulse =100μs, the disturbance range that can be collected is [0,5k), which meets most application scenarios.

[0105] Example 2: Based on Example 1, a new PZT is added at 710m-720m as disturbance 2. In combination with the bandpass sampling theorem, the sampling frequency f=100MSa / s is set, the local spatial position is 450m-750m, the trigger delay τ=450ns, and the recording length RL=300. The amplitude waveforms of disturbances 1 and 2 can be represented by the waveforms at any point between 525m-575m and 710m-720m. The phase waveform of the disturbance signal recovered by the local spatial data acquisition method based on the bandpass sampling theorem is as follows: Figure 4 As shown in the figure, the horizontal axis represents the time T of the acquisition event; the vertical axis represents the phase value. The phase waveform of disturbance 1 can be represented by the phase of any position within the stable area of ​​580m to 700m after the end of the first disturbance (580m), as shown in the figure. Figure 4 (a); and the phase in the stable region 720m~750m after the end of disturbance 2 (720m) contains the phases of all previous disturbances, such as Figure 4 (b) shows the phase waveform of disturbance 2, which is the difference between (b) and (a). Figure 4 (c) According to T pulse = 100μs, the actual sampleable fiber length is 10km, while the local spatial data acquisition method can successfully recover the phase of the disturbance signal by collecting data from only 300m of fiber. Therefore, when collecting disturbance events of the same time T at the same sampling frequency, the traditional acquisition method collects 33 times more data than the local spatial data acquisition method, i.e., k = 33.

[0106] The results of the above two implementation cases show that the present invention can reliably recover the phase of single-point / multi-point disturbances and significantly reduce the amount of data collected. Under the same sampling frequency and data duration, the amount of data collected by the traditional acquisition method is k times that of the local spatial data acquisition method, where

[0107]

[0108] Wherein, L is the length of the optical fiber under test.

[0109] In summary, the present invention proposes a method for extracting the phase of external disturbance events based on local spatial data, which effectively reduces data volume and alleviates system storage space. Using an optimized phase unwrapping algorithm to perform phase unwrapping on the collected local spatial data reduces data processing time and ensures real-time monitoring of the system.

[0110] It should be noted that although the embodiments of the present invention described above are illustrative, they are not intended to limit the present invention. Therefore, the present invention is not limited to the above-mentioned specific embodiments. Without departing from the principles of the present invention, any other embodiments obtained by those skilled in the art under the guidance of the present invention are deemed to be within the protection of the present invention.

Claims

1. A method for extracting the phase of an external disturbance event based on local spatial data, characterized by: The steps are as follows: Step 1: Determine the fiber segments L1 to L2 that require current attention. Step 2: Determine the fiber segment L1 to L2 that needs attention. The local spatial position to be collected is L1-l1 to L2+l2; Step 3: According to the determined local space position, set The trigger delay τ of the synchronous trigger pulse and the data record length RL after the trigger delay; The trigger delay τ is: τ=t ′ ×(L1-l1) The data record length RL is: <h2 style=";text-align:left;direction:ltr">RL≥(L2-L1+l1+l2)×t<h2 style=";text-align:left;direction:ltr"> ′ <h2 style=";text-align:left;direction:ltr"> ×f Step 4: Collect the intermediate frequency data under n consecutive synchronous trigger pulses, that is, when the trigger edge of each synchronous trigger pulse arrives, start collecting intermediate frequency data of length RL after a delay of τ, thereby obtaining a local spatial intermediate frequency data matrix IF of size n×RL; Step 5: Perform orthogonal demodulation on the local spatial intermediate frequency data matrix IF to obtain the initial phase matrix θ; Step 6: Use the optimized phase unwrapping algorithm to unwrap the initial phase matrix θ, restore the true value of the phase, and obtain the true phase matrix Θ; that is: Step 6.1: Perform spatial difference operation on the initial phase matrix θ to obtain the spatial difference matrix θ 1 ; Step 6.2: Spatial difference matrix θ 1 Perform phase unwrapping along the time direction to obtain the unwrapped phase matrix θ 2 ; Step 6.3: The phase matrix θ after unwrapping 2 Perform time difference operation to obtain the real phase matrix Θ; Step 7: Extract the phase of the external disturbance event based on the real phase matrix Θ, that is, the phase of any position in the stable region after the end point L2 of the optical fiber segment currently in focus in the real phase matrix Θ; The above L1 is the starting point of the fiber segment that needs to be paid attention to, and L2 is the end point of the fiber segment that needs to be paid attention to; l1 is the pre-reserved fiber length of the fiber segment that needs to be paid attention to, and l2 is the post-reserved fiber length of the fiber segment that needs to be paid attention to, l1≥SR, l2≥SR, SR is The spatial resolution of t ′ is the time required for light to travel 1 meter in the optical fiber; f is The sampling frequency is τ, the trigger delay is RL, and the number of pulses is n.

2. The method for extracting the phase of an external disturbance event based on local spatial data according to claim 1, wherein the steps 1, the optical fiber segments L1-L2 that currently require attention are determined by a manual designation method or an adaptive method.

3. The method for extracting the phase of an external disturbance event based on local spatial data according to claim 2, characterized in that: The specific process of using adaptive method to determine the fiber segments L1 and L2 that need attention is as follows: First, the traditional data acquisition method is used to collect the intermediate frequency signal within a certain period of time after a trigger pulse; Then, these intermediate frequency signals are demodulated and divided according to the sampling points under a single modulation pulse to obtain a time-space matrix containing the intermediate frequency signal amplitudes of M×N sampling points, where M is the number of data frames and N is the period T of a single modulation pulse. pulse The number of sampling points under ; Finally, the differential accumulation algorithm is used to locate the fiber segment range where the disturbance occurs approximately on the spatiotemporal matrix of the intermediate frequency signal amplitude, and the located fiber segment range where the disturbance occurs approximately is taken as the fiber segment L1-L2 that needs attention.

4. The method for extracting the phase of an external disturbance event based on local spatial data according to claim 1, wherein: In step 2, the spatial resolution SR is: Where c is the speed of light in vacuum, w is The modulation pulse width of the acousto-optic modulator, n eff is the refractive index of the sensing fiber core.

5. The method for extracting the phase of an external disturbance event based on local spatial data according to claim 1 is characterized in that: In step 3, the sampling frequency f is: Where f0 is The frequency shift of the acousto-optic modulator is: B is the bandwidth of the intermediate frequency signal, m is an integer, 1≤m≤j, j is The integer part of .

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