A high spatial resolution brillouin strain sensing method

Abstract

The application provides a high spatial resolution Brillouin strain sensing measurement method and relates to the technical field of optical fiber communication.The technical points of the application include that the application reconstructs a more sharpened and clear Brillouin gain spectrum distribution by using Brillouin information in the time domain without increasing the hardware facilities of the Brillouin optical time domain analysis (BOTDA) system, and then performs self-averaging denoising on the reconstructed Brillouin gain spectrum distribution by using frequency domain information, so as to improve the signal-to-noise ratio; then the center frequency of each Brillouin gain spectrum, i.e., the distributed Brillouin frequency shift, is obtained by curve fitting on the distributed Brillouin gain spectrum, and then the strain amount is obtained according to the Brillouin frequency shift.The application enhances the spatial resolution of the BOTDA, effectively reduces the fitting error of the Brillouin frequency shift, and further improves the measurement accuracy of the optical fiber strain amount.

Description

Technical Field

[0001] This invention relates to the field of optical fiber communication technology, and more specifically to a high spatial resolution Brillouin strain sensing measurement method. Background Technology

[0002] The principle of distributed fiber optic strain sensing is as follows: two beams of light are input to both ends of the fiber, and the scattered signals returning from the fiber are calculated into strain and temperature changes. When the pump beam and probe beam meet in the fiber, and the frequency difference is within the Brillouin spectrum, a Brillouin scattering effect occurs, and the intensity of the probe beam is altered by the pump beam. By sweeping the probe beam, the Brillouin gain spectrum characteristics at each location point in the fiber can be measured. The Brillouin frequency shift can be extracted from the Brillouin gain spectrum. Since the Brillouin frequency shift has a linear relationship with the stress and temperature of the fiber within a certain range, the strain and temperature distribution at each location point in the fiber can be calculated by measuring the Brillouin gain spectrum.

[0003] Traditional BOTDA (Brillouin optical time domain analysis) is based on a pump-probe structure, where a pump pulse and a continuous probe are injected relative to each other into the fiber under test. The measured Brillouin signal is the result of the combined effect of the sub-Brillouin signals corresponding to the various sub-pulses of the pump pulse. The positioning uncertainty is within a pulse width range, meaning the spatial resolution of the system corresponds to the pulse width of the pump pulse. Reducing the pulse width can usually improve spatial resolution; however, due to phonon lifetime limitations, the acoustic field is not fully established after the pulse width is less than 10 ns, leading to a rapid deterioration in the signal-to-noise ratio of the Brillouin signal. Simultaneously, the Brillouin spectral pattern broadens significantly, and the frequency sweep range increases.

[0004] While existing technologies, whether special pulse schemes or algorithm demodulation schemes, can effectively improve spatial resolution, they do not fully utilize the time and frequency domain information of the distributed Brillouin gain spectrum and still have many limitations. In particular, there is a problem that the signal-to-noise ratio of the Brillouin signal drops sharply after algorithm demodulation. Summary of the Invention

[0005] To address this, the present invention proposes a high spatial resolution Brillouin strain sensing measurement method in an attempt to solve or at least alleviate at least one of the problems mentioned above.

[0006] A high spatial resolution Brillouin strain sensing measurement method includes the following steps:

[0007] Step 1: Measure the Brillouin gain spectrum of the optical fiber under test using a BOTDA system; the optical fiber under test includes multiple splice points.

[0008] Step 2: Demodulate and denoise the Brillouin gain spectrum;

[0009] Step 3: Perform curve fitting on the demodulated and denoised Brillouin gain spectrum to obtain the center frequency of each Brillouin gain spectrum, i.e., the distributed Brillouin frequency shift.

[0010] Step 4: Calculate the dependent variable based on the Brillouin frequency shift.

[0011] Furthermore, the specific process of step one includes:

[0012] A narrow-linewidth fiber laser is used as the light source and splits into two paths via a fiber coupler. The upper branch beam is intensity-modulated by EOM1 to generate pulsed light, with the EOM1 drive signal coming from an AWG. Subsequently, the pulsed light is amplified by EDFA1 and used as pump light. The lower branch beam is carrier-suppressed by EOM2 and modulated with a first-order double-sideband signal to serve as probe light. The EOM2 drive signal comes from a sinusoidal microwave signal output from a microwave source. The pump pulse light and the dual-frequency probe light are injected into the fiber under test in opposite directions after passing through a fiber circulator and a fiber isolator, respectively. The dual-frequency probe light passes through an optical circulator and a tunable fiber Bragg grating filter, and the -1st-order sideband is selected as the Brillouin signal. A PD is used to detect the Brillouin signal, using AC output mode. An oscilloscope is used to acquire data. The polarization states of the two beams and the optical experimental instruments are all aligned to the slow axis.

[0013] Furthermore, the specific process of step two includes:

[0014] Step 2: Extract the rising edge of the Brillouin gain spectrum and take its derivative to obtain the nonlinear weighting coefficient matrix;

[0015] Step 22: Reconstruct the Brillouin gain spectrum distribution;

[0016] Steps 2 and 3: Perform self-averaging denoising on the reconstructed Brillouin gain spectrum.

[0017] Furthermore, the nonlinear weighting coefficient matrix described in step two-one is expressed as follows:

[0018]

[0019] In the formula, a1, a2, ..., a M The Brillouin gain, or weighting coefficient, is the weighting factor for the sub-pulse.

[0020] Furthermore, the specific process of step two-two includes: based on the nonlinear weighting coefficient matrix A (R+M-1)×R The normalized waveform of the corresponding Brillouin response, i.e., the reconstructed Brillouin gain spectrum distribution, is obtained by calculating according to the following formula:

[0021]

[0022] In the formula, Y R×NThis represents the normalized waveform of the Brillouin response, i.e., the reconstructed Brillouin gain spectrum distribution. This represents the Brillouin gain spectrum distribution of the entire optical fiber under test.

[0023] Furthermore, the specific steps in steps two and three include:

[0024] The rising edges of multiple Brillouin signals at different frequencies are selected, and multiple nonlinear weighting coefficient matrices are obtained by differentiation. Multiple reconstructed Brillouin gain spectrum distributions are calculated, and the multiple reconstructed Brillouin gain spectrum distributions are averaged and denoised.

[0025] Furthermore, the curve fitting described in step three includes the Lorentz fitting method.

[0026] Furthermore, the specific process of step four includes:

[0027] The formula for calculating the strain of each segment of the optical fiber under test is as follows:

[0028]

[0029] In the formula, Δε i Represents the dependent variable; BFS i BFS represents the Brillouin frequency shift value at the i-th sampling point. REF This represents the reference Brillouin frequency shift value for each fiber segment; The strain coefficient represents the Brillouin frequency shift.

[0030] The beneficial technical effects of this invention are:

[0031] This invention, without increasing the hardware of the BOTDA system, considers the significant information redundancy in the Brillouin gain spectrum distribution. It reconstructs a sharper and clearer Brillouin gain spectrum distribution using Brillouin information in the time domain. Then, it uses frequency domain information to perform self-averaging denoising on the reconstructed Brillouin gain spectrum distribution, thereby improving the signal-to-noise ratio. Finally, by curve fitting the distributed Brillouin gain spectrum, the center frequency of each Brillouin gain spectrum, i.e., the distributed Brillouin frequency shift, can be obtained. The strain value is then calculated based on the Brillouin frequency shift. This invention enhances the spatial resolution of BOTDA, effectively reduces the fitting error of the Brillouin frequency shift, and thus improves the measurement accuracy of fiber strain. Attached Figure Description

[0032] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings. Several embodiments of the invention are illustrated in the drawings by way of example and not limitation, wherein:

[0033] Figure 1This is a flowchart of a high spatial resolution Brillouin strain sensing measurement method according to an embodiment of the present invention;

[0034] Figure 2 This is a schematic diagram of the Brillouin gain spectrum distribution measured by the BOTDA system in an embodiment of the present invention;

[0035] Figure 3 This is a schematic diagram of the Brillouin gain spectrum distribution obtained by measurement in an embodiment of the present invention;

[0036] Figure 4 This is a schematic diagram of the Brillouin gain spectrum distribution after differential processing in an embodiment of the present invention;

[0037] Figure 5 This is a schematic diagram of the final Brillouin gain spectrum distribution obtained in an embodiment of the present invention;

[0038] Figure 6 This is a schematic diagram of the Brillouin frequency shift distribution obtained after curve fitting in an embodiment of the present invention. Detailed Implementation

[0039] The principles and spirit of the invention will now be described with reference to several exemplary embodiments. It should be understood that these embodiments are given merely to enable those skilled in the art to better understand and implement the invention, and are not intended to limit the scope of the invention in any way. Rather, these embodiments are provided to make this disclosure more thorough and complete, and to fully convey the scope of this disclosure to those skilled in the art.

[0040] Those skilled in the art will recognize that embodiments of the present invention can be implemented as a system, apparatus, device, method, or computer program product. Therefore, this disclosure can be specifically implemented in the following forms: entirely hardware, entirely software (including firmware, resident software, microcode, etc.), or a combination of hardware and software. It should be understood herein that any number of elements in the accompanying drawings is for illustrative purposes only and not as a limitation, and any naming is for distinction only and has no limiting meaning.

[0041] This invention provides a high spatial resolution Brillouin strain sensing measurement method, such as... Figure 1 As shown, the method includes the following steps:

[0042] Step 1: Measure the Brillouin gain spectrum of the optical fiber under test using a BOTDA system; the optical fiber under test includes multiple splice points.

[0043] According to an embodiment of the present invention, the process of measuring the Brillouin gain spectrum is as follows: a narrow-linewidth fiber laser is used as the light source and splits into two paths through a fiber coupler; the upper branch beam is intensity-modulated by EOM1 to generate pulsed light, and the driving signal of EOM1 comes from AWG; subsequently, the pulsed light is amplified by EDFA1 and used as pump light; the lower branch beam is carrier-suppressed by EOM2 and modulated with a first-order double-sideband signal to serve as probe light; the driving signal of EOM2 comes from a sinusoidal microwave signal output from a microwave source; the pump pulse light and the dual-frequency probe light are injected into the fiber under test in opposite directions after passing through a fiber circulator and a fiber isolator, respectively; the dual-frequency probe light passes through an optical circulator and a tunable fiber Bragg grating filter, and the -1st order sideband is selected as the Brillouin signal; a PD is used to detect the Brillouin signal, using AC output mode; an oscilloscope is used to acquire data; the polarization states of the two beams and the optical experimental instruments are all aligned to the slow axis.

[0044] Step 2: Demodulate and denoise the Brillouin gain spectrum;

[0045] According to an embodiment of the present invention, firstly, the rising edge of the Brillouin gain spectrum is extracted and its derivative is calculated to obtain the nonlinear weighting coefficient matrix; then, the Brillouin gain spectrum distribution is reconstructed; finally, the reconstructed Brillouin gain spectrum is subjected to self-averaging denoising.

[0046] Step 3: Perform curve fitting on the demodulated and denoised Brillouin gain spectrum to obtain the center frequency of each Brillouin gain spectrum, i.e., the distributed Brillouin frequency shift; the curve fitting includes the Lorentz fitting method.

[0047] Step 4: Calculate the dependent variable based on the Brillouin frequency shift.

[0048] In this embodiment, preferably, the nonlinear weighting coefficient matrix is ​​represented as:

[0049]

[0050] In the formula, a1, a2, ..., a M The Brillouin gain, or weighting coefficient, is the weighting factor for the sub-pulse.

[0051] In this embodiment, preferably, based on the nonlinear weighting coefficient matrix A (R+M-1)×R The normalized waveform of the corresponding Brillouin response, i.e., the reconstructed Brillouin gain spectrum distribution, is obtained by calculating according to the following formula:

[0052]

[0053] In the formula, Y R×N This represents the normalized waveform of the Brillouin response, i.e., the reconstructed Brillouin gain spectrum distribution. This represents the Brillouin gain spectrum distribution of the entire optical fiber under test.

[0054] In this embodiment, preferably, the rising edges of multiple Brillouin signals at different frequencies are selected, and multiple nonlinear weighting coefficient matrices are obtained by differentiation. Multiple reconstructed Brillouin gain spectrum distributions are calculated, and the multiple reconstructed Brillouin gain spectrum distributions are averaged and denoised.

[0055] In this embodiment, preferably, the formula for calculating the strain of each segment of the optical fiber to be tested is as follows:

[0056]

[0057] In the formula, Δε i Represents the dependent variable; BFS i BFS represents the Brillouin frequency shift value at the i-th sampling point. REF This represents the reference Brillouin frequency shift value for each fiber segment; The strain coefficient represents the Brillouin frequency shift.

[0058] Another embodiment of the present invention provides a high spatial resolution Brillouin strain sensing measurement method, firstly, using as... Figure 2 The BOTDA system shown measures the Brillouin gain spectrum distribution. A narrow-linewidth fiber laser serves as the light source, splitting into two paths via a 90:10 fiber coupler. The upper branch beam undergoes intensity modulation via EOM1 to generate pulsed light, with the EOM1 drive signal originating from CH1 of the AWG. This pulsed light is then amplified by EDFA1 and used as the pump light. The lower branch beam undergoes carrier-suppressed first-order double-sideband modulation via EOM2 and serves as the probe light. The EOM2 drive signal originates from a sinusoidal microwave signal output from a microwave source. The pump pulse and dual-frequency probe light are injected into the fiber under test (BUT) in opposite directions after passing through a fiber circulator and a fiber isolator, respectively. The dual-frequency probe light passes through an optical circulator and a tunable fiber Bragg grating (TFBG) filter, selecting the -1st-order sideband as the Brillouin signal. A PD is used to probe the Brillouin signal; AC output mode is used to improve the signal-to-noise ratio. An oscilloscope is used to acquire data. The BUT fiber is a polarization-maintaining fiber, and the polarization states of both beams and the optical experimental instruments are aligned to the slow axis. The acquired Brillouin gain spectrum distribution is demodulated and denoised using digital signal processing.

[0059] The spatial resolution of a BOTDA system corresponds to the pulse width of the pump pulse. Typically, reducing the pump pulse width is necessary to improve spatial resolution. However, once a spatial resolution of 1m is achieved, further improvements using this method face the following limitations: 1) Phonon lifetime effect: The Brillouin signal gain increases exponentially with the pump pulse width. If the pump pulse width is less than the phonon lifetime, the signal-to-noise ratio of the Brillouin signal is weak because the acoustic field has not yet reached a steady state, thus reducing the measurement accuracy and measurement length of the BOTDA system; 2) Brillouin gain spectrum broadening: As the pump pulse width decreases, especially below 10ns, the spectrum broadening phenomenon is very obvious. The measured Brillouin gain spectrum is the convolution of the intrinsic Brillouin gain spectrum and the pump pulse spectrum. The measured Brillouin gain spectrum broadens sharply as the pump pulse width decreases, and the energy in the spectrum is dispersed, which reduces the signal-to-noise ratio of the Brillouin signal and increases the fitting error of the Brillouin frequency shift.

[0060] Therefore, this invention proposes an algorithm to enhance spatial resolution by taking the derivative of the Brillouin signal at the rising edge to obtain nonlinear weighting coefficients.

[0061] In traditional BOTDA measurements, the pump light is modulated as a pulsed light, and the probe light is a continuous light of a single frequency; both are injected relative to each other into the fiber under test (BUT). When the probe light frequency is scanned so that the frequency difference between the two is within the SBS (Spectral Breakdown) region of the fiber, the pump pulsed light continuously interacts with the probe continuous light along the BUT, amplifying its power—this is the Brillouin signal. By measuring the duration of this amplification, the position of the BUT can be located. This Brillouin signal is ultimately received by a photodetector through a circulator for photoelectric conversion, and the electrical signal is collected by a digital oscilloscope or data acquisition card. The distributed Brillouin gain spectrum can be obtained by frequency scanning of the probe light.

[0062] A relatively long pump pulse can be considered as a series of discrete, extremely narrow sub-pulses connected in series over time, that is:

[0063]

[0064] In the formula, x j (t) represents the j-th sub-pulse, x j (t)=p0[u(t-jτ+τ)-u(t-jτ)], p0 represents peak power, τ is the sub-pulse interval, u(t) is the unit step function; M represents the number of sub-pulses, M=t p / τ.

[0065] Each sub-pulse interacts with the probe light via SBS, generating a sub-Brillouin response waveform. These waveforms share the same normalized waveform y(t), but adjacent sub-Brillouin response waveforms have a fixed delay τ. Since SBS is a nonlinear process, these curves exhibit different Brillouin gains a. j That is, the weighting coefficient. The Brillouin signal y corresponding to the pump pulse light. BS (t is formed by the superposition of these sub-Brillouin responses:)

[0066]

[0067] The spatial resolution of the normalized waveform y(t) of the Brillouin response corresponds to the pulse width of the sub-pulse. However, in actual data acquisition, the pulse width of the sub-pulse is only limited by the sampling interval of the oscilloscope. Due to the superposition effect, the spatial resolution of the Brillouin signal degrades from the pulse width of the sub-pulse to the pulse width of the pump pulse. During this process, a rising edge y appears at the beginning and end of the Brillouin signal, respectively. R (t) and a falling edge y F (t), formula (2) can be written in the following matrix form:

[0068]

[0069]

[0070] In the formula, R represents the normalized waveform y of the Brillouin response. R×1 Length; A (R+M-1)×R This represents the nonlinear weighting coefficient matrix.

[0071]

[0072] From formula (4), it can be seen that the nonlinear weighting coefficient matrix A (R+M-1)×R It is a striped sparse matrix whose internal elements correspond to the Brillouin gain 'a' of each sub-pulse. j When the Brillouin frequency shift corresponding to the rising or falling edge of the sensing fiber is relatively uniform, the amplitude of the normalized waveform at that position is constant, i.e., y(t) = y0. According to the formula, the Brillouin gain a at the rising and falling edges... j It is proportional to the first derivative of a continuous Brillouin signal or the difference result of a discrete Brillouin signal, that is:

[0073] a j ∝y′ R [(j-1)τ]

[0074] a j ∝-y′ F [(M-j+2)τ] (5)

[0075] Typically, the rising edge function y R (t) has a higher signal-to-noise ratio, so the rising edge function is chosen to calculate the nonlinear weighting coefficient matrix A. (R+M-1)×R In existing algorithms, the weighting coefficients simply represent the proportions of each part of the pump pulse. However, the nonlinear weighting coefficient matrix in this embodiment establishes a direct correspondence between each sub-pulse of the pump pulse light and the sub-Brillouin signal, taking into account the exponential growth of the Brillouin signal when the acoustic field is established.

[0076] Next, the Brillouin gain spectrum distribution along the entire fiber under test is represented in matrix form as follows:

[0077]

[0078]

[0079] In the formula, N represents the number of sweep frequencies; Y R×N This represents the normalized waveform of the Brillouin response, i.e., the reconstructed Brillouin gain spectrum distribution.

[0080] Due to the calculation of the gain coefficient a j When performing a derivative, the noise is amplified, resulting in a very low signal-to-noise ratio (SNR) for the reconstructed Brillouin gain spectrum distribution. To improve the SNR, the frequency domain information of the Brillouin gain spectrum distribution is utilized. Multiple sets of Brillouin signals with similar frequencies are selected and demodulated repeatedly at their rising edges to obtain multiple sets of reconstructed Brillouin gain spectrum distributions. Finally, averaging the reconstructed Brillouin gain spectrum distributions improves the SNR.

[0081] This invention fully utilizes the time-domain and frequency-domain information of the measured Brillouin gain spectrum distribution. After demodulation, the spatial resolution of the reconstructed Brillouin gain spectrum distribution corresponds to the pulse width of the sub-pulse. Theoretically, for an ideal square-wave pulse light, the spatial resolution can correspond to the sampling time interval of an oscilloscope or acquisition card. To obtain higher spatial resolution, the subdivision factor needs to be increased, which will increase noise during demodulation. In practical applications, the spatial resolution is affected by the rising and falling edges of the pump pulse light. If the rising and falling edges of the pump pulse light are relatively steep, the effect caused by edge changes can be ignored; if the edges are relatively slow, the effect caused by the edges needs to be taken into account. Therefore, an energy weighting ratio is defined:

[0082]

[0083] In the formula, p j P represents the sub-pulse power. 50％ This represents half of the maximum power, with the pulse width corresponding to a time range exceeding that power; p 10％ This represents 10% of the maximum power. The time range exceeding this power corresponds to the start of the rising edge and the end of the falling edge.

[0084] Set a threshold P_P = 5%. When P_P < 5%, meaning the energy below the pulse width accounts for only about one-twentieth of the total pulse energy, the pulse edge can be considered relatively steep, and subdivision only needs to be performed within the pulse width range. When P_P > 5%, the pulse edge is relatively gentle, and the energy below the pulse width cannot be ignored, requiring subdivision within the range of the rising edge start and falling edge end. A square wave pulse with rising and falling edges can be simulated using a super-Gaussian function.

[0085] x Gaussain =exp[-(2t / t p ) NG (8)

[0086] In the formula, NG represents the order.

[0087] This invention utilizes the above algorithm to demodulate and denoise the Brillouin gain spectrum distribution, including the following steps:

[0088] Step 1: Extract the rising edge and obtain the nonlinear weighting coefficient matrix A;

[0089] According to an embodiment of the present invention, since the differentiation process is equivalent to a high-pass filter, high-frequency noise is amplified, causing a sharp deterioration in the signal-to-noise ratio, which directly affects the signal-to-noise ratio of the processed data. The first 8 ns (800 mm) of Brillouin signal data corresponds to the rising edge y. R (t), the first 8ns data of the first derivative of this signal is y R '(t), whose elements correspond to {a j}, j = 1, 2, 3, ..., 800. Arrange these elements according to formula (4) to obtain the nonlinear weight coefficient matrix A.

[0090] Step 2: Reconstruct the Brillouin gain spectrum distribution;

[0091] According to an embodiment of the present invention, based on formula (3), the reconstructed Brillouin signal corresponding to a Brillouin frequency shift of 10.88 GHz can be obtained, and its signal-to-noise ratio (SNR) is estimated to be 17 dB, that is, the SNR is reduced by 31 dB after algorithm processing. According to formula (6), the normalized waveform of the Brillouin response corresponding to each sweep frequency is calculated using the nonlinear weighting coefficient matrix A, that is, the distribution Y of the reconstructed Brillouin gain spectrum.

[0092] Step 3: Self-averaging noise reduction;

[0093] According to an embodiment of the present invention, in order to improve the signal-to-noise ratio of the reconstructed Brillouin gain spectrum distribution, 20 rising edges of Brillouin signals in the frequency range of 10.862 GHz to 10.900 GHz were selected, and 20 nonlinear weighting coefficient matrices {A} were obtained by differentiation.l}, l=1,2,3,……,20. Then, according to formula (6), calculate the 20 reconstructed Brillouin gain spectrum distributions Y respectively. l We then averaged and denoised these 20 sets of data.

[0094] Step 4: Calculate the Brillouin frequency shift distribution;

[0095] According to an embodiment of the present invention, the reconstructed Brillouin gain spectrum distribution after 20 self-averaging denoising operations is Lorentz fitted to obtain the Brillouin frequency shift distribution.

[0096] To explore the limiting performance of the demodulation algorithm of this invention, two fiber segments with different Brillouin frequency shifts, with lengths of 15 mm and 8 mm respectively, were inserted into an 11.0 m fiber under test. First, a BOTDA system with an 8.0 ns single-pulse pump light was used for detection, with a spatial resolution of 80 cm. The measured Brillouin gain spectrum distribution is shown below. Figure 3 As shown, the boundaries are very blurry. After magnifying the image at the insertion segment location, the Brillouin gain spectrum does not change significantly, meaning the two insertion segments cannot be identified. Next, using the optimized DPP-BOTDA scheme as the reference group, transient pulse pairs of 8.05 ns and 7.97 ns were selected as pump pulses, with a pulse width difference of 0.08 ns, corresponding to a spatial resolution of 8 mm. The Brillouin gain spectrum distribution after differentiation is shown below. Figure 4 As shown, the Brillouin gain spectrum narrows, and the spatial resolution is enhanced. The 15mm insertion segment can be clearly observed, but the boundary of the 8mm insertion segment is blurry and cannot be accurately identified. Subsequently, the demodulation algorithm of this invention is used to... Figure 3 The Brillouin gain spectrum distribution is demodulated to obtain the reconstructed Brillouin gain spectrum distribution. After 30 iterations of self-averaging denoising, the final Brillouin gain spectrum distribution is as follows: Figure 5 As shown in the enlarged image on the right, the spectral shape of the Brillouin gain spectrum has not narrowed, but the spatial resolution has been enhanced, and both the 15mm and 8mm insertion segments can be identified. Compared to the DPP-BOTDA scheme, the demodulation algorithm of this invention produces a clearer boundary between the two insertion segments in the demodulated Brillouin gain spectrum. Finally, the intensity of the area within the white box is first enhanced, and then median filtering is applied to the entire spectrum. The resulting Brillouin gain spectrum distribution is shown below. Figure 6 As shown in the figure, the white scatter line represents the Brillouin frequency shift distribution obtained by fitting the Lorentz curve. The lengths of the two insertion segments are 15 mm and 8 mm, which are consistent with the actual values. Therefore, the spatial resolution is improved by 100 times, reaching the millimeter level.

[0097] Furthermore, although the operations of the method of the present invention are described in a specific order in the accompanying drawings, this does not require or imply that these operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

[0098] While the spirit and principles of the invention have been described with reference to several specific embodiments, it should be understood that the invention is not limited to the disclosed specific embodiments, and the division of aspects does not imply that features in these aspects cannot be combined for benefit; such division is merely for ease of description. The invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A high spatial resolution Brillouin strain sensing measurement method, characterized in that, Includes the following steps: Step 1: Measure the Brillouin gain spectrum of the optical fiber under test using the BOTDA system. The optical fiber under test includes multiple splice points; Step 2: Demodulate and denoise the Brillouin gain spectrum; The specific process includes: Step 2: Extract the rising edge of the Brillouin gain spectrum and differentiate it to obtain the nonlinear weighting coefficient matrix; the nonlinear weighting coefficient matrix is ​​expressed as: ； In the formula, The Brillouin gain of the sub-pulse is the weighting coefficient. Step 22: Reconstruct the Brillouin gain spectrum distribution; the specific process includes: based on the nonlinear weighting coefficient matrix... The normalized waveform of the corresponding Brillouin response, i.e., the reconstructed Brillouin gain spectrum distribution, is obtained by calculating according to the following formula: ； In the formula, This represents the normalized waveform of the Brillouin response, i.e., the reconstructed Brillouin gain spectrum distribution. This represents the Brillouin gain spectrum distribution of the entire optical fiber under test. Steps 2 and 3: Perform self-averaging denoising on the reconstructed Brillouin gain spectrum; including: selecting the rising edges of multiple Brillouin signals at different frequencies, obtaining multiple nonlinear weighting coefficient matrices by differentiation, calculating multiple reconstructed Brillouin gain spectrum distributions, and averaging denoising on the multiple reconstructed Brillouin gain spectrum distributions. Step 3: Perform curve fitting on the demodulated and denoised Brillouin gain spectrum to obtain the center frequency of each Brillouin gain spectrum, i.e., the distributed Brillouin frequency shift. Step 4: Calculate the dependent variable based on the Brillouin frequency shift.

2. The high spatial resolution Brillouin strain sensing measurement method according to claim 1, characterized in that, The specific process of step one includes: A narrow-linewidth fiber laser is used as the light source and splits into two paths via a fiber coupler. The upper branch beam is intensity-modulated by EOM1 to generate pulsed light, with the EOM1 drive signal coming from an AWG. Subsequently, the pulsed light is amplified by EDFA1 and used as pump light. The lower branch beam is carrier-suppressed by EOM2 and modulated with a first-order double-sideband signal to serve as probe light. The EOM2 drive signal comes from a sinusoidal microwave signal output from a microwave source. The pump pulse light and the dual-frequency probe light are injected into the fiber under test in opposite directions after passing through a fiber circulator and a fiber isolator, respectively. The dual-frequency probe light passes through an optical circulator and a tunable fiber Bragg grating filter, and the -1st-order sideband is selected as the Brillouin signal. A PD is used to detect the Brillouin signal, using AC output mode. An oscilloscope is used to acquire data. The polarization states of the two beams and the optical experimental instruments are all aligned to the slow axis.

3. The high spatial resolution Brillouin strain sensing measurement method according to claim 1, characterized in that, The curve fitting described in step three includes the Lorentz fitting method.

4. The high spatial resolution Brillouin strain sensing measurement method according to claim 3, characterized in that, Step four includes the following specific steps: The formula for calculating the strain of each segment of the optical fiber under test is as follows: ； In the formula, Indicates the dependent variable; Indicates the first Brillouin frequency shift values ​​at each sampling point; This represents the reference Brillouin frequency shift value for each fiber segment; The strain coefficient represents the Brillouin frequency shift.

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