BOTDR system Brillouin gain spectrum correction method and system based on symmetric kernel

Abstract

The invention provides a BOTDR system Brillouin gain spectrum correction method and system based on a symmetric kernel, and belongs to the technical field of optical fiber sensing. The method comprises the following steps: acquiring Brillouin gain spectrum information along a sensing optical fiber; acquiring amplitude-frequency responses of the balanced photoelectric detector and the band-pass filter in a full frequency band by using a vector network analyzer; performing convolution processing on the obtained Brillouin gain spectrum information along the sensing optical fiber and the amplitude-frequency response of the balanced photoelectric detector and the band-pass filter in the full frequency band to obtain a corrected Brillouin gain spectrum; lorentz fitting is carried out on the corrected Brillouin gain spectrum to extract Brillouin frequency shift, and the Brillouin frequency shift is converted into temperature and strain information. The spectral line symmetry and the signal-to-noise ratio are improved, the symmetry of the corrected Brillouin gain spectrum is remarkably enhanced, the phenomena of peak offset and asymmetric broadening caused by system bandwidth limitation are eliminated, and the extraction precision of the Brillouin gain spectrum is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the field of optical fiber sensing, and particularly relates to a Brillouin gain spectrum correction method and system for a BOTDR system based on a symmetric kernel. Background Technique

[0002] The statements in this part only provide background technical information related to the present invention, and do not necessarily constitute prior art.

[0003] Brillouin Optical Time Domain Reflectometer (BOTDR) is a distributed optical fiber sensing technology based on the principle of self-published Brillouin scattering, which can realize distributed measurement of strain and temperature along the optical fiber line, and has the unique advantage of single-end access. With its excellent scalability and environmental adaptability, BOTDR technology has been widely used in the health monitoring of large-scale structures such as long-distance bridges, dams, and tunnels, as well as in the fields of geological disaster warning and energy pipeline safety management.

[0004] The BOTDR system usually realizes the quantitative inversion of strain and temperature by detecting the Brillouin Frequency Shift (BFS) in the Brillouin Gain Spectrum (BGS). Among them, the extraction accuracy of BFS directly determines the measurement accuracy of temperature or strain, while the spatial resolution affects the positioning ability of the fault or abnormal area. Therefore, the measurement accuracy of BFS and its spatial resolution become the core goals for improving the performance of the BOTDR system.

[0005] In recent years, in order to improve the spatial resolution and BFS extraction accuracy of the BOTDR system, in terms of signal processing, various methods based on similarity matching, time-frequency analysis, neural networks, etc. have been gradually developed from the initially adopted Levenberg-Marquardt fitting algorithm, effectively improving the measurement accuracy of BFS and suppressing the random fluctuation of BFS. In terms of system structure, the proposal of schemes such as Dual-Pulse BOTDR (DPP-BOTDR) has achieved higher spatial resolution through high-time-precision pulse configuration.

[0006] However, in a frequency-swept Brillouin optical time domain reflectometer (FS-BOTDR) system, it is usually necessary to first convert the optical signal into an electrical signal through a balanced photodetector (BPD), and then perform frequency selection filtering on the beat frequency signal through a bandpass filter (BPF) to obtain the Brillouin gain spectrum (BGS). Ideally, the demodulated BGS can truly reflect the intrinsic characteristics of the optical fiber. However, in an actual system, due to non-ideal factors such as the uneven amplitude-frequency response, limited bandwidth, center frequency offset, and asymmetric transition band of the "balanced photodetector (BPD) + bandpass filter (BPF)", it will cause distortion, broadening of the BGS spectrum line, and a decrease in the signal-to-noise ratio, ultimately resulting in problems such as error offset and reduced accuracy in frequency shift demodulation. These distortions are particularly significant in high measurement accuracy or extreme environments, severely restricting the application effect of the BOTDR system in engineering practice.

[0007] To address the above limitations, technicians have conducted extensive and in-depth research. It has been found that the non-ideal amplitude-frequency response of the BPF is the root cause of BGS distortion and BFS extraction error. Although reducing the filter bandwidth can reduce this impact to a certain extent, it will introduce new problems such as an extended system response time and reduced spatial resolution, making it difficult to balance the dual requirements of frequency accuracy and time-domain resolution.

[0008] Therefore, there is an urgent need for a method that can effectively compensate for the Brillouin gain spectrum distortion caused by the non-ideal bandwidth of the photodetector and the bandpass filter to improve the accuracy of BFS demodulation and the overall measurement reliability of the system. Summary of the Invention

[0009] To overcome the above deficiencies of the prior art, the present invention provides a method and system for correcting the Brillouin gain spectrum of a BOTDR system based on a symmetric kernel. By performing convolution processing on the original BGS and the amplitude-frequency response of the "BPD + BPF", it equivalently realizes the convolution operation between the ideal Brillouin gain spectrum of the optical fiber and a symmetric kernel function, thus effectively solving the spectral distortion (asymmetry, power fluctuation) and asymmetric distortion phenomenon caused by the non-ideal device bandwidth of the system. Therefore, without changing the hardware structure of the system, it significantly improves the spectral symmetry and signal-to-noise ratio, and significantly enhances the accuracy and stability of Brillouin frequency shift extraction.

[0010] To achieve the above object, one or more embodiments of the present invention provide the following technical solutions:

[0011] The first aspect of the present invention provides a method for correcting the Brillouin gain spectrum of a BOTDR system based on a symmetric kernel;

[0012] The method for correcting the Brillouin gain spectrum of a BOTDR system based on a symmetric kernel includes:

[0013] Build a mathematical model for the frequency-domain demodulation process of the FS-BOTDR system to obtain the Brillouin gain spectrum information along the sensing fiber;

[0014] Use a vector network analyzer to obtain the amplitude-frequency response of the balanced photodetector and the band-pass filter within the full frequency band;

[0015] Perform convolution processing on the obtained Brillouin gain spectrum information along the sensing fiber and the amplitude-frequency response of the balanced photodetector and the band-pass filter within the full frequency band to obtain the corrected Brillouin gain spectrum;

[0016] Perform Lorentz fitting on the corrected Brillouin gain spectrum to extract the Brillouin frequency shift and convert it into temperature and strain information.

[0017] As a further technical solution, the process of building the mathematical model for the frequency-domain demodulation process of the FS-BOTDR system is as follows:

[0018] Obtain the frequency of the output signal of the microwave source within the scanning period;

[0019] From the frequency-domain perspective, the amplitude signal obtained within each frequency scanning period is equivalent to the product superposition of the ideal Brillouin gain spectrum of the optical fiber and the amplitude-frequency response of the balanced photodetector and the band-pass filter at the corresponding frequency points;

[0020] Based on the sampling theorem, when the frequency sweep step size is less than or equal to half of the filter bandwidth, discrete summation is performed on the Brillouin gain information.

[0021] As a further technical solution, the process of building the mathematical model for the frequency-domain demodulation process of the FS-BOTDR system to obtain the Brillouin gain spectrum information along the sensing fiber is as follows:

[0022] After the beat-frequency processing of the backward spontaneous Brillouin scattering signal, extract the Brillouin gain information at specific frequency points through a band-pass filter with a specific center frequency;

[0023] By stepwise adjusting the output frequency of the microwave source, the Brillouin gain spectrum is translated as a whole in the frequency domain to construct a complete Brillouin gain spectrum.

[0024] As a further technical solution, in the process of using a vector network analyzer to obtain the amplitude-frequency response of the balanced photodetector and the band-pass filter within the full frequency band, constructing a symmetric kernel function is also included.

[0025] As a further technical solution, the symmetric kernel function is:

[0026]

[0027] In the formula, A is the amplitude scaling factor, and its value is equal to the maximum value of the autocorrelation function of the filter amplitude-frequency response, that is:

[0028]

[0029] Λ(m) is defined as the standard trigonometric function as follows:

[0030]

[0031] Where M is the discrete half-width parameter, and it satisfies M = B / v step , where B is the bandwidth of the bandpass filter.

[0032] As a further technical solution, the corrected Brillouin gain spectrum is as follows:

[0033]

[0034] Where G Corrected [p, z] is the corrected Brillouin gain spectrum; where p is the shift factor in the convolution operation, and its physical meaning represents the discrete sampling points in the frequency domain, used to identify the abscissa position of the Brillouin gain spectrum; z is the position of the optical fiber to be measured; A is the amplitude scaling factor; Λ is the standard trigonometric function; g[n, z] represents the discretized observed signal after frequency translation of the ideal Brillouin gain spectrum at the optical fiber axial position z.

[0035] As a further technical solution, the process of performing Lorentz fitting on the corrected Brillouin gain spectrum to extract the Brillouin frequency shift includes:

[0036] Perform Lorentz curve fitting on the corrected Brillouin gain spectrum, and by adjusting the parameters, make the fitting curve satisfy the least squares error criterion at each frequency point; as shown in the following formula:

[0037]

[0038] Where g0 represents the Brillouin gain, v B represents the Brillouin center frequency, and Δv represents the full width at half maximum of the Brillouin gain spectrum;

[0039] After the fitting is completed, according to the center frequency v corresponding to the peak of the fitting curve B Extract the Brillouin frequency shift of the BOTDR system, and convert it into temperature and strain information to achieve precise perception of temperature or strain changes.

[0040] The second aspect of the present invention provides a BOTDR system Brillouin gain spectrum correction system based on a symmetric kernel.

[0041] The BOTDR system Brillouin gain spectrum correction system based on a symmetric kernel includes:

[0042] The Brillouin gain spectrum acquisition module is configured to: construct a mathematical model of the frequency-domain demodulation process in the FS-BOTDR system and obtain the Brillouin gain spectrum information along the sensing optical fiber;

[0043] The amplitude-frequency response acquisition module is configured to: use a vector network analyzer to obtain the amplitude-frequency response of the balanced photodetector and the band-pass filter within the full frequency band;

[0044] The Brillouin gain spectrum correction module is configured to: perform convolution processing on the obtained Brillouin gain spectrum information along the sensing optical fiber and the amplitude-frequency response of the balanced photodetector and the band-pass filter within the full frequency band to obtain the corrected Brillouin gain spectrum;

[0045] The Lorentz fitting module is configured to: perform Lorentz fitting on the corrected Brillouin gain spectrum to extract the Brillouin frequency shift and convert it into temperature and strain information.

[0046] The third aspect of the present invention provides a computer-readable storage medium, on which a program is stored, and when the program is executed by a processor, it implements the steps in the Brillouin gain spectrum correction method of the BOTDR system based on a symmetric kernel as described in the first aspect of the present invention.

[0047] The fourth aspect of the present invention provides an electronic device, including a memory, a processor, and a program stored on the memory and executable on the processor. When the processor executes the program, it implements the steps in the Brillouin gain spectrum correction method of the BOTDR system based on a symmetric kernel as described in the first aspect of the present invention.

[0048] The above one or more technical solutions have the following beneficial effects:

[0049] By performing discrete convolution processing on the original BGS and the amplitude-frequency response of "balanced photodetector (BPD) + band-pass filter (BPF)", the present invention equivalently realizes the convolution operation of the ideal Brillouin gain spectrum of the optical fiber and the autocorrelation function of the amplitude-frequency response of "balanced photodetector (BPD) + band-pass filter (BPF)" (constituting a symmetric kernel). Thus, without changing the system hardware structure, the spectral line symmetry and signal-to-noise ratio are significantly improved. The symmetry of the corrected Brillouin gain spectrum is significantly enhanced, and the peak shift and asymmetric broadening phenomena caused by system bandwidth limitations are eliminated.

[0050] Since the corrected Brillouin gain spectrum can be approximated as the convolution of a Lorentzian or Gaussian Brillouin gain spectrum and a symmetric kernel function, this method can effectively suppress the spectral distortion caused by the non-ideal bandwidth of the system, obtain a more symmetric and closer-to-intrinsic-structure Brillouin gain spectrum, and significantly improve the extraction accuracy of the Brillouin gain spectrum.

[0051] Advantages of additional aspects of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The accompanying drawings forming a part of this specification are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not unduly limit the present invention.

[0053] Figure 1 It is a flowchart of the method for the first embodiment.

[0054] FIG. 2 is an evaluation of Brillouin frequency shift extraction accuracy in the first embodiment. Among them, FIG. 2(a) is the original Brillouin gain spectrum at the 9000m position and its Lorentz curve fitting result; FIG. 2(b) is the corrected Brillouin gain spectrum at the 9000m position and its Lorentz curve fitting result; FIG. 2(c) is the Brillouin frequency shift of the standard optical fiber demodulated based on the original data and the corrected data.

[0055] Figure 3 It is a schematic diagram of the distribution of Brillouin frequency shift demodulated by the method of the present invention at different temperatures in the first embodiment.

[0056] Figure 4 It is the Brillouin frequency shift at different temperatures in the first embodiment.

[0057] Figure 5 It is a comparison diagram of the uncertainty distribution between the method of the present invention and the traditional method in temperature measurement in the first embodiment.

[0058] Figure 6 It is a system structure diagram of the second embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0059] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0060] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention.

[0061] In the case of no conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0062] The present invention establishes a mathematical model for the spectrum scanning process of the FS-BOTDR system in the frequency domain, revealing that the Brillouin gain spectrum (BGS) detected by this system is essentially the discrete cross-correlation function between the ideal Brillouin gain spectrum and the amplitude-frequency response of the "balanced photodetector (BPD) + bandpass filter (BPF)". Thus, it is further clarified that the non-ideal amplitude-frequency response of the "BPD + BPF" is the fundamental cause of spectral line distortion and demodulation error.

[0063] Based on this theory, the present invention effectively solves the spectral distortion (asymmetry, power fluctuation) and asymmetric distortion phenomenon caused by the non-ideal device bandwidth of the system by performing convolution processing on the original BGS and the amplitude-frequency response of the "BPD + BPF", thereby equivalently realizing the convolution operation between the ideal Brillouin gain spectrum of the optical fiber and a symmetric kernel function, and significantly improving the accuracy and stability of Brillouin frequency shift extraction.

[0064] The method of the present invention will be described in detail below in conjunction with specific embodiments.

[0065] Embodiment 1

[0066] This embodiment discloses a method for correcting the Brillouin gain spectrum of a BOTDR system based on a symmetric kernel;

[0067] As Figure 1 shown, the method for correcting the Brillouin gain spectrum of a BOTDR system based on a symmetric kernel includes:

[0068] Step S1, constructing a mathematical model for the frequency-domain demodulation process in the FS-BOTDR system to obtain the Brillouin gain spectrum information along the sensing optical fiber;

[0069] By constructing a mathematical model for the frequency-domain demodulation process in the FS-BOTDR system, after the backward spontaneous Brillouin scattering signal is beat-frequency processed, it passes through a bandpass filter with a center frequency of f C to extract the Brillouin gain information at specific frequency points. By stepwise adjusting the output frequency v ref of the microwave source, the Brillouin gain spectrum is globally translated in the frequency domain, thereby constructing a complete Brillouin gain spectrum.

[0070] In this embodiment, the Brillouin gain spectrum detected in the FS-BOTDR system is the discrete cross-correlation between the ideal Brillouin gain spectrum of the optical fiber and the amplitude-frequency response of the "balanced photodetector (BPD) + bandpass filter (BPF)". Further explanation and verification are carried out by constructing a mathematical model for the frequency-domain demodulation process in the FS-BOTDR system. Specifically:

[0071] Let the frequency of the signal output by the microwave source in the m-th frequency sweep period be:

[0072] v ref = vB` -f C +mv step , m ∈ [-k, k], m ∈ Z (1)

[0073] In Equation (1), v ref , vB`, v step and f C are respectively the frequency of the output signal of the microwave source, the Brillouin frequency shift of the optical fiber, the frequency sweep step of the microwave source (determining the system frequency resolution), and the center frequency of the band-pass filter; the integer m is the frequency sweep index, and its value range m ∈ [-k, k] is determined by the bandwidth B = 2k·v step .

[0074] Analyzing from the frequency domain perspective, the amplitude signal obtained within each frequency scan period can be mathematically equivalent to the product superposition of the ideal Brillouin gain spectrum of the optical fiber and the amplitude-frequency response of "balanced photodetector (BPD) + band-pass filter (BPF)" at the corresponding frequency points, expressed as:

[0075]

[0076] In Equation (2), g Measured (mv step , z) is the Brillouin gain information at the position z of the optical fiber under test detected in the m-th frequency sweep period; h(v) is the continuous amplitude-frequency response of "balanced photodetector (BPD) + band-pass filter (BPF)"; g(v, z) is the ideal Brillouin gain spectrum at the position z of the optical fiber under test.

[0077] Based on the sampling theorem, when the frequency sweep step v step satisfies the Nyquist condition (v step ≤ B / 2, B is the filter bandwidth): the continuous integral can be approximated as a discrete summation to avoid spectral aliasing. Therefore, Equation (2) can be discretized as:

[0078]

[0079] In Equation (3), h[n] represents the discretized form of the continuous amplitude-frequency response h(v) of "balanced photodetector (BPD) + band-pass filter (BPF)", and its physical meaning is that during the frequency sweep process, the continuous frequency response h(v) is uniformly sampled with the frequency step v step as the sampling interval to obtain the discrete sequence, that is: h[n] = h(nv step ); g[n, z] represents the discretized observation signal of the ideal Brillouin gain spectrum at the axial position z of the optical fiber after frequency translation. Its physical essence is: when the reference light is at m = 0 in Equation (2), the system aligns the peak frequency of the Brillouin gain spectrum to the center frequency f of the band-pass filter CNearby, and then the signal is swept with a step size of v step After quantization sampling, a two-dimensional discrete Brillouin gain spectrum matrix with n as the discrete frequency index and z as the spatial position coordinate is formed, that is: g[n,z] = g(nv step +v B -f C ,z), then the detected Brillouin gain spectrum of the system is the discrete cross-correlation of the ideal Brillouin gain spectrum of the optical fiber and the amplitude-frequency response of "balanced photodetector (BPD) + band-pass filter (BPF)", that is:

[0080] g Measured [m,z] = R hg [m,z], m ∈ [-k,k] (4)

[0081] In formula (4), R hg represents the correlation operator; m can be regarded as the lag in the correlation operation.

[0082] Based on the above process, in step S2, a vector network analyzer (VNA) is used to obtain the amplitude-frequency response of the balanced photodetector and the band-pass filter in the full frequency band, and discretization processing is performed to obtain the discrete amplitude-frequency response sequence h[n] of "balanced photodetector (BPD) + band-pass filter (BPF)".

[0083] Furthermore, in step S2, a symmetric kernel function is also constructed. Specifically, according to the properties of the autocorrelation function, the autocorrelation function of the amplitude-frequency response of "balanced photodetector (BPD) + band-pass filter (BPF)" presents a symmetric narrow triangular shape, and the main lobe width and shape depend on the bandwidth characteristics of the filter.

[0084]

[0085] In formula (5), A is the amplitude scaling factor, and its value is equal to the maximum value of the autocorrelation function of the filter amplitude-frequency response, that is Λ(m) is the standard trigonometric function, defined as:

[0086]

[0087] In formula (6), M is the discrete half-width parameter, which satisfies M = B / v step (B is the bandwidth of the band-pass filter).

[0088] Step S3, convolve the obtained Brillouin gain spectrum information along the sensing optical fiber with the amplitude-frequency response of the balanced photodetector and the band-pass filter in the full frequency band to obtain the corrected Brillouin gain spectrum;

[0089] The Brillouin gain spectrum g MeasuredConvolution of [m, z] with the discrete amplitude-frequency response sequence h[m] of "balanced photodetector (BPD) + bandpass filter (BPF)" gives:

[0090]

[0091] In the formula, h[m] is the expression form of the discrete amplitude-frequency response sequence in the convolution operation process.

[0092] Substituting Equation (2) and exchanging the summation order gives:

[0093]

[0094] According to the autocorrelation characteristic of the filter amplitude-frequency response in Equation (5), the second term in Equation (8) can be expressed as:

[0095]

[0096] Finally, substituting Equation (9) into Equation (8) gives:

[0097]

[0098] Therefore, in the present invention, by convolving the original Brillouin gain spectrum with the amplitude-frequency response of "balanced photodetector (BPD) + bandpass filter (BPF)", it is equivalently realized to convolve the ideal Brillouin gain spectrum of the optical fiber with a symmetric kernel. Since the corrected Brillouin gain spectrum can be approximated as the convolution of a Lorentzian or Gaussian Brillouin gain spectrum with a symmetric kernel function, this method can effectively suppress the spectral distortion caused by the non-ideal bandwidth of the system and obtain a more symmetric and closer-to-intrinsic-structure Brillouin gain spectrum.

[0099] Step S4: Perform Lorentz fitting on the corrected Brillouin gain spectrum to extract the Brillouin frequency shift and convert it into temperature and strain information.

[0100] For the corrected Brillouin gain spectrum in step S3, perform Lorentz curve fitting, and by adjusting the parameters in the model, make the fitting curve satisfy the least squares error criterion at each frequency point. As shown in the following formula:

[0101]

[0102] In the formula, g0 represents the Brillouin gain, v B represents the Brillouin center frequency, and Δv represents the full width at half maximum of the Brillouin gain spectrum.

[0103] After fitting, according to the center frequency v corresponding to the peak of the fitting curve B, the Brillouin frequency shift of the BOTDR system can be extracted and converted into temperature and strain information, thus realizing the precise sensing function of the present invention for temperature or strain changes. Specifically, since there is a good linear relationship between the Brillouin frequency shift in the optical fiber and temperature and strain, the extracted Brillouin frequency shift can be further converted into temperature or strain information distributed along the optical fiber, thereby achieving the goal of distributed sensing and structural health monitoring.

[0104] Furthermore, in order to verify the feasibility and robustness of the method of the present invention, comparative experiments were also carried out for verification in this embodiment. Evaluation of Brillouin frequency shift extraction accuracy, sensitivity to pulse width, sensitivity to the number of averages and its signal-to-noise ratio improvement effect, system linearity evaluation, system uncertainty evaluation.

[0105] Figures 2(a)-2(c) show the evaluation results of the Brillouin frequency shift extraction accuracy in the method of the present invention. The evaluation results show that after being processed by this method, the BGS structure is significantly improved, the spectral symmetry is enhanced, the noise level is significantly reduced, the fitting determination coefficient is increased to 0.997, the center frequency is 10740.37 MHz, deviating from the theoretical value by only 0.37 MHz, and the frequency shift extraction accuracy is greatly improved. The method of the present invention can effectively eliminate the influence of the non-ideality of the system bandwidth on the measurement accuracy, improve the spectral line symmetry and signal-to-noise ratio of the BGS, and significantly improve the extraction accuracy of the Brillouin frequency shift, verifying its application value and effect in the actual BOTDR system.

[0106] Figure 3 Shows the distribution curve of the BFS obtained by demodulating this method with the change of temperature. Figure 4 The linear fitting effects of the BFS and temperature under two methods are compared. The results show that the linear determination coefficient between the BFS extracted by the traditional method and temperature is 0.99982, while the linear determination coefficient between the BFS extracted by this method and temperature is further increased to 0.99990, indicating that this method has good temperature sensitivity and stability and can accurately reflect the BFS drift trend corresponding to the actual temperature change.

[0107] Figure 5 Shows the comparison of the uncertainty distributions in temperature measurement between this method and the traditional method. It can be seen that the standard deviation measured by this method is mainly concentrated below 0.275 °C, while the standard deviation distribution of the traditional method is wider, and 90% of the measurement results need to reach within 0.375 °C to cover. This indicates that this method has lower uncertainty and higher stability in temperature demodulation, significantly improving the measurement accuracy and reliability.

[0108] Embodiment 2

[0109] This embodiment discloses a Brillouin gain spectrum correction system for a BOTDR system based on a symmetric kernel;

[0110] As Figure 6 shown, the Brillouin gain spectrum correction system of the BOTDR system based on a symmetric core includes:

[0111] A Brillouin gain spectrum acquisition module, configured to: construct a mathematical model of the frequency-domain demodulation process in the FS-BOTDR system, and acquire Brillouin gain spectrum information along the sensing optical fiber;

[0112] An amplitude-frequency response acquisition module, configured to: use a vector network analyzer to acquire the amplitude-frequency response of the balanced photodetector and the band-pass filter within the full frequency band;

[0113] A Brillouin gain spectrum correction module, configured to: perform convolution processing on the obtained Brillouin gain spectrum information along the sensing optical fiber and the amplitude-frequency response of the balanced photodetector and the band-pass filter within the full frequency band to obtain the corrected Brillouin gain spectrum;

[0114] A Lorentz fitting module, configured to: perform Lorentz fitting on the corrected Brillouin gain spectrum to extract the Brillouin frequency shift and convert it into temperature and strain information.

[0115] Embodiment III

[0116] The purpose of this embodiment is to provide a computer-readable storage medium.

[0117] A computer-readable storage medium, on which a computer program is stored, and when the program is executed by a processor, it implements the steps in the Brillouin gain spectrum correction method of the BOTDR system based on a symmetric core as described in Embodiment 1.

[0118] Embodiment IV

[0119] The purpose of this embodiment is to provide an electronic device.

[0120] An electronic device, including a memory, a processor, and a program stored on the memory and executable on the processor, and when the processor executes the program, it implements the steps in the Brillouin gain spectrum correction method of the BOTDR system based on a symmetric core as described in Embodiment 1.

[0121] The steps involved in the devices in the above Embodiments II, III, and IV correspond to those in Method Embodiment 1, and the specific implementation manners can refer to the relevant description part of Embodiment 1. The term "computer-readable storage medium" should be understood to include a single medium or multiple media including one or more instruction sets; it should also be understood to include any medium that can store, encode, or carry an instruction set for execution by a processor and enable the processor to execute any method in the present invention.

[0122] Those skilled in the art should understand that the above-mentioned modules or steps of the present invention can be implemented by a general-purpose computer device. Optionally, they can be implemented by program codes executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be separately fabricated into individual integrated circuit modules, or multiple modules or steps among them can be fabricated into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0123] Although the specific implementation manners of the present invention have been described above in conjunction with the accompanying drawings, it is not a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications or deformations that can be made without creative efforts on the basis of the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for correcting the Brillouin gain spectrum of a BOTDR system based on a symmetric kernel, characterized in that: Construct a mathematical model of the frequency-domain demodulation process in the FS-BOTDR system to obtain the Brillouin gain spectrum information along the sensing optical fiber; Use a vector network analyzer to obtain the amplitude-frequency response of the balanced photodetector and the band-pass filter in the full frequency band; Perform convolution processing on the obtained Brillouin gain spectrum information along the sensing optical fiber and the amplitude-frequency response of the balanced photodetector and the band-pass filter in the full frequency band to obtain the corrected Brillouin gain spectrum; Perform Lorentz fitting on the corrected Brillouin gain spectrum to extract the Brillouin frequency shift and convert it into temperature and strain information.

2. The Brillouin gain spectrum correction method for the BOTDR system based on a symmetric core according to claim 1, wherein The process of constructing the mathematical model of the frequency-domain demodulation process in the FS-BOTDR system is as follows: Obtain the frequency of the output signal of the microwave source within the scanning period; From the frequency-domain perspective, the amplitude signal obtained in each frequency scanning period is equivalent to the product superposition of the ideal Brillouin gain spectrum of the optical fiber and the amplitude-frequency response of the balanced photodetector and the band-pass filter at the corresponding frequency points; Based on the sampling theorem, when the frequency sweep step size is less than or equal to half of the filter bandwidth, discrete summation is performed on the Brillouin gain information.

3. The Brillouin gain spectrum correction method for the BOTDR system based on a symmetric core according to claim 1, wherein The process of constructing the mathematical model of the frequency-domain demodulation process in the FS-BOTDR system to obtain the Brillouin gain spectrum information along the sensing optical fiber is as follows: After the backward spontaneous Brillouin scattering signal is subjected to beat frequency processing, the Brillouin gain information at specific frequency points is extracted through a band-pass filter with a specific center frequency; By stepwise adjusting the output frequency of the microwave source, the Brillouin gain spectrum is translated as a whole in the frequency domain to construct a complete Brillouin gain spectrum.

4. The Brillouin gain spectrum correction method for the BOTDR system based on a symmetric core according to claim 1, characterized in that In the process of using a vector network analyzer to obtain the amplitude-frequency response of the balanced photodetector and the band-pass filter in the full frequency band, a symmetric kernel function is also constructed.

5. The Brillouin gain spectrum correction method for the BOTDR system based on a symmetric core according to claim 4, wherein The symmetric kernel function is: In the formula, A is the amplitude scaling factor, and its value is equal to the maximum value of the autocorrelation function of the filter amplitude-frequency response, that is: Λ(m) is the standard trigonometric function defined as: where M is the discrete half-width parameter, which satisfies M = B / v step , and B is the bandwidth of the band-pass filter.

6. The Brillouin gain spectrum correction method for the BOTDR system based on a symmetric core according to claim 1, wherein, The corrected Brillouin gain spectrum is: where G Corrected [p, z] is the corrected Brillouin gain spectrum; where p is the shift factor in the convolution operation, and its physical meaning represents the discrete sampling points in the frequency domain, which is used to identify the abscissa position of the Brillouin gain spectrum; z is the position of the optical fiber to be measured; A is the amplitude scaling factor; Λ is the standard trigonometric function; g[n, z] represents the discretized observed signal after frequency translation of the ideal Brillouin gain spectrum at the fiber axial position z.

7. The Brillouin gain spectrum correction method for the BOTDR system based on a symmetric core according to claim 1, characterized in that, The process of performing Lorentz fitting on the corrected Brillouin gain spectrum to extract the Brillouin frequency shift includes: Perform Lorentz curve fitting on the corrected Brillouin gain spectrum, and by adjusting the parameters, make the fitting curve satisfy the least squares error criterion at each frequency point; as shown in the following formula: where g0 represents the Brillouin gain, v B represents the Brillouin center frequency, and Δv represents the full width at half maximum of the Brillouin gain spectrum; After the fitting is completed, according to the center frequency v corresponding to the peak value of the fitting curve B Extract the Brillouin frequency shift of the BOTDR system and convert it into temperature and strain information.

8. Brillouin gain spectrum correction system for BOTDR system based on symmetric kernel, characterized in that, Including: A Brillouin gain spectrum acquisition module, configured to: construct a mathematical model of the frequency-domain demodulation process in the FS-BOTDR system to obtain the Brillouin gain spectrum information along the sensing optical fiber; An amplitude-frequency response acquisition module, configured to: use a vector network analyzer to obtain the amplitude-frequency response of the balanced photodetector and the band-pass filter in the full frequency band; A Brillouin gain spectrum correction module, configured to: perform convolution processing on the obtained Brillouin gain spectrum information along the sensing optical fiber and the amplitude-frequency response of the balanced photodetector and the band-pass filter in the full frequency band to obtain the corrected Brillouin gain spectrum; A Lorentz fitting module, configured to: perform Lorentz fitting on the corrected Brillouin gain spectrum to extract the Brillouin frequency shift and convert it into temperature and strain information.

9. A computer-readable storage medium having a program stored thereon, characterized in that, When the program is executed by a processor, it implements the steps in the Brillouin gain spectrum correction method of the symmetric-core-based BOTDR system according to any one of claims 1-7.

10. An electronic device, comprising a memory, a processor, and a program stored on the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the Brillouin gain spectrum correction method of the symmetric-core-based BOTDR system according to any one of claims 1-7.

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