OFDR measurement method and system based on correlation spectrum self-compensation

Abstract

The embodiment of the present application provides an OFDR measurement method and system based on correlation spectrum self-compensation, which relates to the field of optical fiber sensing technology, and includes the following steps: collecting a reference signal and a measurement signal; using a fast Fourier transform to convert both the frequency domain data of the reference signal and the frequency domain data of the measurement signal into distance domain data, and respectively calculating the spatial resolution length of the reference signal and the spatial resolution length of the measurement signal; adjusting the spectrum information of the reference signal so that the spectrum of the reference signal and the spectrum of the measurement signal match within a wide strain range; dividing the distance domain data of the reference signal and the distance domain data of the measurement signal into sliding windows based on a preset spatial resolution, and performing an inverse fast Fourier transform on the data in each window to convert it into frequency domain data; calculating the spectrum offset between the reference signal and the measurement signal by a cross-correlation algorithm, and demodulating to obtain the strain distribution along the optical fiber.

Description

Technical Field

[0001] The present application relates to the field of optical fiber sensing technology, and in particular to an OFDR measurement method and system based on correlation spectrum self-compensation. Background Art

[0002] Distributed fiber optic sensing technology uses optical fiber as a sensing and transmission medium, and realizes distributed real-time monitoring of environmental parameters (such as strain, temperature, and vibration) by analyzing the scattering effect of light waves in optical fiber (such as Rayleigh scattering, Raman scattering, and Brillouin scattering). Distributed fiber optic sensing technology has been widely used in bridge safety monitoring, civil engineering detection, tunnel fire warning, geological exploration, and other fields due to its strong anti-electromagnetic interference ability, high spatial resolution, and long sensing distance.

[0003] Among the related technologies, Optical Frequency Domain Reflectometry (OFDR), as a representative of distributed fiber optic sensing technology, has shown important value in high-precision monitoring fields such as aerospace due to its millimeter-level high spatial resolution, high sensitivity and compact structure.

[0004] However, when the OFDR system improves spatial resolution or measures a large strain range, the cross-correlation between the reference signal and the measurement signal will be significantly reduced, resulting in multiple peaks and false peaks in the cross-correlation results, making it difficult to accurately extract strain information. Summary of the invention

[0005] The embodiments of the present application provide an OFDR measurement method and system based on correlation spectrum self-compensation to solve the technical problem in the related art that when the OFDR system improves the spatial resolution or measures a large strain range, the cross-correlation between the reference signal and the measurement signal will be significantly reduced, resulting in multiple peaks and false peaks in the cross-correlation results, making it difficult to accurately extract strain information.

[0006] In a first aspect, an embodiment of the present application provides an OFDR measurement method based on correlation spectrum self-compensation, comprising the following steps:

[0007] Collecting a reference signal and a measurement signal; wherein the reference signal is frequency domain data that does not contain strain information, and the measurement signal is frequency domain data that contains strain information;

[0008] The frequency domain data of the reference signal and the frequency domain data of the measurement signal are converted into distance domain data by using fast Fourier transform, and the spatial resolution length of the reference signal and the spatial resolution length of the measurement signal are calculated respectively;

[0009] Adjusting the spectrum information of the reference signal so that the spectrum of the reference signal matches the spectrum of the measurement signal within a wide strain range;

[0010] Dividing the distance domain data of the reference signal and the distance domain data of the measurement signal into sliding windows based on a preset spatial resolution, and converting the data in each window into frequency domain data by inverse fast Fourier transform;

[0011] The spectrum offset between the reference signal and the measurement signal is calculated by the cross-correlation algorithm, and the strain distribution along the optical fiber is obtained by demodulation.

[0012] In a feasible implementation, adjusting the spectrum information of the reference signal so that the spectrum of the reference signal matches the spectrum of the measurement signal within a wide strain range specifically includes:

[0013] The reference signal spectrum position with the highest correlation with the measured signal is searched in a wide frequency domain, and the frequency domain coordinates of the reference signal are corrected by a self-compensation algorithm so that the spectrum of the reference signal and the spectrum of the measured signal can match in a wide strain range.

[0014] In a feasible implementation, the preset spatial resolution The width satisfies the following formula:

[0015]

[0016] in, express The number of Rayleigh scattering points in represents the speed of light, represents the refractive index of the optical fiber, Indicates the frequency tuning range of the tunable laser source.

[0017] In a feasible implementation, the cross-correlation algorithm includes the following steps:

[0018] Perform complex conjugate multiplication of the frequency domain data of the reference signal and the frequency domain data of the measurement signal;

[0019] Perform inverse Fourier transform on the product result to generate a cross-correlation function sequence;

[0020] The spectrum shift is determined by locating the peak of the cross-correlation function and eliminating multi-peak interference.

[0021] In a second aspect, an embodiment of the present application further provides an OFDR measurement system based on correlation spectrum self-compensation, which adopts an OFDR measurement method based on correlation spectrum self-compensation in any technical solution of the first aspect, and the system includes a tunable laser source and a sensing optical fiber, wherein the tunable laser source is configured to inject detection light into the sensing optical fiber;

[0022] The system is configured to perform the following steps:

[0023] Injecting detection light into the sensing optical fiber through a tunable laser source, and collecting frequency domain data of the reference signal under no-strain conditions and frequency domain data of the measurement signal under strain conditions;

[0024] The frequency domain data of the reference signal and the frequency domain data of the measurement signal are converted into distance domain data by using fast Fourier transform, and the spatial resolution length of the reference signal and the spatial resolution length of the measurement signal are calculated respectively;

[0025] Dividing the distance domain data of the reference signal and the distance domain data of the measurement signal into sliding windows based on a preset spatial resolution, and converting the data in each window into frequency domain data by inverse fast Fourier transform;

[0026] Adjusting the spectrum information of the reference signal so that the spectrum of the reference signal matches the spectrum of the measurement signal within a wide strain range;

[0027] The spectrum offset between the reference signal and the measurement signal is calculated by the cross-correlation algorithm, and the strain distribution along the optical fiber is obtained by demodulation.

[0028] In a feasible implementation, the system further includes: a first coupler, a second coupler, a third coupler, a Mach-Zehnder interferometer, a circulator, a first polarization controller, a polarization beam splitter, a sensing optical fiber, and a data acquisition card;

[0029] The output end of the tunable laser source is connected to the input end of the first coupler, the first output end of the first coupler is connected to the input end of the Mach-Zehnder interferometer, and the second output end of the first coupler is connected to the input end of the second coupler; the output end of the Mach-Zehnder interferometer is connected to the first input end of the data acquisition card; the first output end of the second coupler is connected to the first input end of the third coupler through the first polarization controller, and the second output end of the second coupler is connected to the first input end of the circulator; the output end of the third coupler is connected to the input end of the polarization beam splitter, and the second input end of the third coupler is connected to the first output end of the circulator; the p end and the s end of the polarization beam splitter output are respectively connected to the second input end and the third input end of the data acquisition card; the second output end of the circulator is connected to the sensing optical fiber through the second polarization controller.

[0030] In a feasible implementation, the frequency modulation range of the tunable laser source is The wavelength is 1510nm to 1610nm, and the line width of the tunable laser source is equal to 100MHz.

[0031] On the first aspect, an embodiment of the present application provides an OFDR measurement method based on correlation spectrum self-compensation. In the embodiment of the present application, by adjusting the spectrum of the reference signal in the frequency domain data, searching for spectrum information matching the reference signal in a wide range of spectrum, and obtaining an array of cross-correlation results, during the demodulation process, even if a demodulation error occurs in the moving window position of the Rayleigh scattering spectrum of a certain reference signal, it will not affect the overall demodulation result. Furthermore, compared with the prior art that directly analyzes the spectrum displacement between the reference signal and the measurement signal, the displacement of the Rayleigh scattering point in the spectrum domain caused by strain is eliminated, and the problem of reduced correlation between the reference signal and the measurement signal caused by large strain stretching under high spatial resolution measurement is eliminated, that is, the correlation between the reference signal and the measurement signal caused by large strain stretching under high spatial resolution measurement is improved, and the spatial mismatch phenomenon at the rear end of the strain stretching position caused by large strain stretching is further eliminated, thereby enhancing the analysis capability of large strains and improving the accuracy of strain analysis positioning.

[0032] In the second aspect, the present application also provides an OFDR measurement system based on correlated spectrum self-compensation, which adopts an OFDR measurement method based on correlated spectrum self-compensation in any technical solution of the first aspect. Therefore, the measurement system has the technical effects of any technical solution of the first aspect, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present application and do not constitute an improper limitation of the present invention. In the drawings:

[0034] Figure 1 1 is a schematic structural diagram of an OFDR measurement system based on correlation spectrum self-compensation provided in an embodiment of the present application;

[0035] Figure 2 This is a data processing flow chart of an OFDR measurement method based on correlation spectrum self-compensation provided in one embodiment of the present application;

[0036] Figure 3 This is a method step diagram of an OFDR measurement method based on correlation spectrum self-compensation provided in one embodiment of the present application;

[0037] Figure 4 yes Figure 3 The specific method steps diagram of S2;

[0038] Figure 5 yes Figure 3 The specific method steps of S5 in FIG.

[0039] Figure 6This is a graph showing the variation of spectral shift with optical fiber length obtained by measuring optical fiber strain information using an OFDR measurement method and system in the prior art provided in an embodiment of the present application;

[0040] Figure 7 The diagram is a graph showing the variation of spectral displacement with optical fiber length obtained by measuring optical fiber strain information using an OFDR measurement method and system based on correlation spectrum self-compensation provided in an embodiment of the present application.

[0041] Description of reference numerals:

[0042] 101-tunable laser source; 102-sensing optical fiber; 103-first coupler; 104-second coupler; 105-third coupler; 106-Mach-Zehnder interferometer; 107-circulator; 108-first polarization controller; 109-polarization beam splitter; 110-second polarization controller; 111-data acquisition card. DETAILED DESCRIPTION

[0043] In order to enable those skilled in the art to better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present application.

[0044] The embodiments of the present application provide an OFDR measurement method and system based on correlation spectrum self-compensation to solve the technical problem in the related art that when the OFDR system improves the spatial resolution or measures a large strain range, the cross-correlation between the reference signal and the measurement signal will be significantly reduced, resulting in multiple peaks and false peaks in the cross-correlation results, making it difficult to accurately extract strain information.

[0045] Figure 1 It is a structural schematic diagram of an OFDR measurement system based on correlation spectrum self-compensation provided in one embodiment of the present application.

[0046] In some examples, reference Figure 1 The OFDR measurement system based on correlation spectrum self-compensation includes a tunable laser source 101, a first coupler 103, a second coupler 104, a third coupler 105, a Mach-Zehnder interferometer 106, a circulator 107, a first polarization controller 108, a polarization beam splitter 109, a sensing optical fiber 102, a data acquisition card 111 and the sensing optical fiber 102.

[0047] Among them, the output end of the tunable laser source 101 is connected to the input end of the first coupler 103, the first output end of the first coupler 103 is connected to the input end of the Mach-Zehnder interferometer 106, and the second output end of the first coupler 103 is connected to the input end of the second coupler 104; the output end of the Mach-Zehnder interferometer 106 is connected to the first input end of the data acquisition card 111; the first output end of the second coupler 104 is connected to the input end of the third coupler 105 through the first polarization controller 108, and the second output end of the second coupler 104 is connected to the first input end of the circulator 107; the first output end of the third coupler 105 is connected to the input end of the polarization beam splitter 109, and the second output end of the third coupler 105 is connected to the second input end of the circulator 107; the p end and the s end outputted by the polarization beam splitter 109 are respectively connected to the second input end and the third input end of the data acquisition card 111, and the output end of the circulator 107 is connected to the sensing optical fiber 102 through the second polarization controller 110.

[0048] In a specific implementation, the continuous laser of the tunable laser source 101 is output to the input end of the first coupler 103. The first coupler 103 is set as a 10 / 90 optical coupler. The first output end of the first coupler 103 outputs 10% of the laser to the input end of the Mach-Zehnder interferometer to provide a trigger signal for the data acquisition card 111. The remaining 90% of the laser is output from the second output end of the first coupler 103 to the input end of the second coupler 104.

[0049] It should be noted that the Mach-Zehnder interferometer 106 includes a beam splitter, that is, the Mach-Zehnder interferometer 106 uses a beam splitter to split the light beam of the tunable laser source 101 into two paths, and then merges them after passing through different paths, and realizes light modulation by detecting the changes in interference fringes caused by the optical path difference between the two beams.

[0050] The second coupler 104 is set as a 1 / 99 optical coupler. The second coupler 104 adjusts 1% of the laser light through the first polarization controller 108 and outputs it to the first input end of the third coupler 105 . The second coupler 104 outputs 99% of the laser light to the circulator 107 .

[0051] The second output end of the second coupler 104 outputs 99% of the laser light to the sensing fiber 102 through the circulator 107 and the second polarization controller 110 , and generates a Rayleigh scattering signal.

[0052] The Rayleigh scattering signal and 1% of the laser are output from the first output end of the circulator 107 to the second input end of the third coupler 105, and are gathered in the third coupler 105 to obtain an interference signal, which is then decomposed into "p" and "s" components by the polarization beam splitter 109, and finally the "p" and "s" lights are collected by the data acquisition card 111.

[0053] Furthermore, in a specific implementation, the data acquisition card 111 needs to collect signals twice, that is, to collect the measurement signal when the sensing optical fiber 102 is strained, and to collect the reference signal when the sensing optical fiber 102 is not strained.

[0054] It should be noted that the sensing optical fiber 102 is configured as a standard single-mode optical fiber.

[0055] Figure 2 This is a data processing flow chart of an OFDR measurement method based on correlation spectrum self-compensation provided in one embodiment of the present application; Figure 3 This is a method step diagram of an OFDR measurement method based on correlation spectrum self-compensation provided in one embodiment of the present application; Figure 4 yes Figure 3 The specific method steps diagram of S2; Figure 5 yes Figure 3 Specific method steps of S5 in FIG.

[0056] In the first aspect, in an OFDR measurement system based on correlation spectrum self-compensation, the embodiment of the present application discloses an OFDR measurement method based on correlation spectrum self-compensation, referring to Figure 2 and Figure 3 , the method comprises the following steps:

[0057] S1: Collect reference signal and measurement signal.

[0058] The reference signal is frequency domain data without strain information, and the measurement signal is frequency domain data containing strain information.

[0059] The signal when strain is applied to the sensing optical fiber 102 is collected by the data acquisition card 111 in the OFDR measurement system based on correlation spectrum self-compensation, which is the measurement signal; the signal when no strain is applied to the sensing optical fiber 102 is collected by the data acquisition card 111 in the OFDR measurement system based on correlation spectrum self-compensation, which is the reference signal.

[0060] The measurement signal is a signal collected by the data acquisition card 111 when strain is applied to the sensing optical fiber 102 , and the reference signal is a signal collected when no strain is applied to the sensing optical fiber 102 .

[0061] It should be noted that when collecting the reference signal and the measurement signal, the parameters of the OFDR measurement system based on correlation spectrum self-compensation are the same.

[0062] S2: The frequency domain data of the reference signal and the frequency domain data of the measurement signal are converted into distance domain data by using fast Fourier transform, and the spatial resolution length of the reference signal and the spatial resolution length of the measurement signal are calculated respectively.

[0063] In the specific implementation, refer to Figure 4 , respectively calculating the spatial resolution length of the reference signal and the spatial resolution length of the measurement signal specifically comprises the following steps:

[0064] S210: Calculate a proportionality factor according to the total length of the optical fiber and the propagation speed of the laser.

[0065] S220: Scale the distance domain data according to the proportional factor so that the range of the distance domain data is consistent with the total length of the optical fiber.

[0066] It should be noted that, in the above steps, the steps used for calculating the spatial resolution length of the reference signal and the steps used for calculating the spatial resolution length of the measurement signal are the same.

[0067] S3: Adjusting the spectrum information of the reference signal so that the spectrum of the reference signal matches the spectrum of the measurement signal within a wide strain range.

[0068] Among them, S3 specifically includes:

[0069] While keeping the preset number of measurement points of spatial resolution unchanged, the spectrum of the reference signal is moved in sequence in a wide frequency domain by means of reference signal self-compensation, and cross-correlation calculations are performed with the measurement signal to obtain cross-correlation array results, thereby searching for the reference signal spectrum position with the highest correlation with the measurement signal, so that the spectrum of the reference signal and the spectrum of the measurement signal can match within a wide strain range.

[0070] In the specific implementation, the reference signal is adjusted in the frequency domain, and the spectrum information matching the measurement signal is searched under a wide spectrum range to eliminate the shift of Rayleigh scattering points in the spectrum domain caused by strain, thereby eliminating the problem of reduced correlation between the reference signal and the measurement signal caused by large strain stretching under high spatial resolution measurement.

[0071] That is, by adjusting the reference signal so that it can better match the measurement signal, the measurement accuracy is improved.

[0072] S4: Divide the distance domain data of the reference signal and the distance domain data of the measurement signal into sliding windows based on a preset spatial resolution, and perform an inverse fast Fourier transform on the data in each window to convert it into frequency domain data.

[0073] It should be noted that the sliding window is used to extract local signal data in the distance domain, and the size of the sliding window corresponds to the preset spatial distribution rate.

[0074] Among them, the preset spatial resolution (sliding window) The width satisfies the following formula:

[0075]

[0076] in, express The number of Rayleigh scattering points in represents the speed of light, represents the refractive index of the optical fiber, Indicates the frequency tuning range of the tunable laser source.

[0077] The strain information is calculated by analyzing the signal data within each sliding window to calculate the strain distribution along the length of the optical fiber.

[0078] The inverse fast Fourier transform converts the signal data in the sliding window from the distance domain to the frequency domain to facilitate further analysis of the frequency components of the signal and thus extract strain information.

[0079] S5: The spectrum offset between the reference signal and the measurement signal is calculated by a cross-correlation algorithm, and the strain distribution along the optical fiber is obtained by demodulation.

[0080] Specifically, refer to Figure 5 , the cross-correlation algorithm includes the following steps:

[0081] S510: Perform complex conjugate multiplication on the reference signal and the frequency domain data of the measurement signal;

[0082] S520: Perform inverse Fourier transform on the product result to generate a cross-correlation function sequence;

[0083] S530: Determine the spectrum displacement by locating the peak of the cross-correlation function and eliminate multi-peak interference.

[0084] In specific implementation, the cross-correlation function is calculated for the reference signal and the measurement signal in each sliding window, and the spectrum offset between the reference signal and the measurement signal is determined by the peak position of the cross-correlation function. That is, the cross-correlation method is used to measure the similarity between two signals and determine the spectrum offset between them.

[0085] On the first aspect, an embodiment of the present application provides an OFDR measurement method based on correlation spectrum self-compensation. In the embodiment of the present application, by adjusting the spectrum of the reference signal in the frequency domain data, searching for spectrum information matching the reference signal in a wide range of spectrum, and obtaining an array of cross-correlation results, during the demodulation process, even if a demodulation error occurs in the moving window position of the Rayleigh scattering spectrum of a certain reference signal, it will not affect the overall demodulation result. Furthermore, compared with the prior art that directly analyzes the spectrum displacement between the reference signal and the measurement signal, the displacement of the Rayleigh scattering point in the spectrum domain caused by strain is eliminated, and the problem of reduced correlation between the reference signal and the measurement signal caused by large strain stretching under high spatial resolution measurement is eliminated, that is, the correlation between the reference signal and the measurement signal caused by large strain stretching under high spatial resolution measurement is improved, and the spatial mismatch phenomenon at the rear end of the strain stretching position caused by large strain stretching is further eliminated, thereby enhancing the analysis capability of large strains and improving the accuracy of strain analysis positioning.

[0086] Second, refer to Figure 1 , the present application also provides an OFDR measurement system based on correlation spectrum self-compensation, adopting an OFDR measurement method based on correlation spectrum self-compensation in any technical solution of the first aspect, the system includes a tunable laser source 101 and a sensing optical fiber 102, wherein the tunable laser source 101 is configured to inject detection light into the sensing optical fiber 102;

[0087] The system is configured to perform the following steps:

[0088] Injecting detection light into the sensing optical fiber 102 through a tunable laser source 101, and collecting frequency domain data of a reference signal under a strain-free condition and collecting frequency domain data of a measurement signal under a strain-existing condition;

[0089] The frequency domain data of the reference signal and the frequency domain data of the measurement signal are converted into distance domain data by using fast Fourier transform, and the spatial resolution length of the reference signal and the spatial resolution length of the measurement signal are calculated respectively;

[0090] Dividing the distance domain data of the reference signal and the distance domain data of the measurement signal into sliding windows based on a preset spatial resolution, and converting the data in each window into frequency domain data by inverse fast Fourier transform;

[0091] Adjusting the spectrum information of the reference signal so that the spectrum of the reference signal matches the spectrum of the measurement signal within a wide strain range;

[0092] The spectrum offset between the reference signal and the measurement signal is calculated by the cross-correlation algorithm, and the strain distribution along the optical fiber is obtained by demodulation.

[0093] In the second aspect, the present application also provides an OFDR measurement system based on correlated spectrum self-compensation, which adopts an OFDR measurement method based on correlated spectrum self-compensation in any technical solution of the first aspect. Therefore, the measurement system has the technical effects of any technical solution of the first aspect, which will not be repeated here.

[0094] In some examples, the measurement system further includes a first coupler 103 , a second coupler 104 , a third coupler 105 , a Mach-Zehnder interferometer 106 , a circulator 107 , a first polarization controller 108 , a polarization beam splitter 109 , a sensing optical fiber 102 , and a data acquisition card 111 .

[0095] The output end of the tunable laser source 101 is connected to the input end of the first coupler 103, the first output end of the first coupler 103 is connected to the input end of the Mach-Zehnder interferometer 106, and the second output end of the first coupler 103 is connected to the input end of the second coupler 104; the output end of the Mach-Zehnder interferometer 106 is connected to the first input end of the data acquisition card 111; the first output end of the second coupler 104 is connected to the first input end of the third coupler 105 through the first polarization controller 108, and the second output end of the second coupler 104 is connected to the first input end of the circulator 107; the output end of the third coupler 105 is connected to the input end of the polarization beam splitter 109, and the second input end of the third coupler 105 is connected to the first output end of the circulator 107; the p end and the s end outputted by the polarization beam splitter 109 are respectively connected to the second input end and the third input end of the data acquisition card 111, and the second output end of the circulator 107 is connected to the sensing optical fiber 102 through the second polarization controller 110.

[0096] In some examples, the frequency tuning range of the tunable laser source 101 is The wavelength is 1510nm to 1610nm, and the line width of the tunable laser source is equal to 100MHz.

[0097] Figure 6 This is a graph showing the variation of spectral shift with optical fiber length obtained by measuring optical fiber strain information using an OFDR measurement method and system in the prior art, provided in an embodiment of the present application.

[0098] Reference Figure 6 ,exist Figure 6In the present invention, the OFDR measurement method based on self-compensation of the correlation spectrum provided in the embodiment of the present application is not adopted. In the existing OFDR system, strain information of 1000με-10000με is applied in sequence at the position of 10.3m-10.6m of the sensing optical fiber 102, and is processed with a preset spatial resolution of 2mm. Among them, curve M1 is a graph showing the change of the spectral shift with the length of the sensing optical fiber 102 when the strain is 1000με; curve M2 is a graph showing the change of the spectral shift with the length of the sensing optical fiber 102 when the strain is 2000με; curve M3 is a graph showing the change of the spectral shift with the length of the sensing optical fiber 102 when the strain is 3000με; curve M4 is a graph showing the change of the spectral shift with the length of the sensing optical fiber 102 when the strain is 4000με; curve M5 is a graph showing the change of the spectral shift with the length of the sensing optical fiber 102 when the strain is 5000με. ; Curve M6 is a graph showing the change of the spectral shift with the length of the sensing optical fiber 102 when the strain is 6000με; Curve M7 is a graph showing the change of the spectral shift with the length of the sensing optical fiber 102 when the strain is 7000με; Curve M8 is a graph showing the change of the spectral shift with the length of the sensing optical fiber 102 when the strain is 8000με; Curve M9 is a graph showing the change of the spectral shift with the length of the sensing optical fiber 102 when the strain is 9000με; Curve M10 is a graph showing the change of the spectral shift with the length of the sensing optical fiber 102 when the strain is 10000με. From Figure 6 It can be seen that the curve graph of M1-M10 has multiple peaks shown by line segment A, making the curve graph difficult to distinguish. In the experiment, it was found that when the strain was higher than 4000με, the curve of the change of the spectrum displacement with the length of the sensing optical fiber 102 began to have more peaks, making the curve graph difficult to distinguish, and it was impossible to distinguish the change trend of the spectrum displacement with the sensing optical fiber.

[0099] Figure 7 The diagram is a graph showing the variation of spectral displacement with optical fiber length obtained by measuring optical fiber strain information using an OFDR measurement method and system based on correlation spectrum self-compensation provided in an embodiment of the present application.

[0100] Reference Figure 7 ,exist Figure 7In the embodiment of the present application, the OFDR measurement method and system based on correlation spectrum self-compensation provided in the embodiment of the present application are used. Similarly, strain information of 1000με-10000με is applied in sequence at the position of 10.3m-10.6m of the sensing optical fiber 102, and it is processed with a preset spatial resolution of 2mm, wherein curve N1 is a curve diagram of the change of the spectral displacement with the length of the sensing optical fiber 102 when the strain is 1000με; curve N2 is a curve diagram of the change of the spectral displacement with the length of the sensing optical fiber 102 when the strain is 2000με; curve N3 is a curve diagram of the change of the spectral displacement with the length of the sensing optical fiber 102 when the strain is 3000με; curve N4 is a curve diagram of the change of the spectral displacement with the length of the sensing optical fiber 102 when the strain is 4000με. Curve N5 is a curve chart showing the change of spectral shift with the length of the sensing optical fiber 102 when the strain is 5000με; Curve N6 is a curve chart showing the change of spectral shift with the length of the sensing optical fiber 102 when the strain is 6000με; Curve N7 is a curve chart showing the change of spectral shift with the length of the sensing optical fiber 102 when the strain is 7000με; Curve N8 is a curve chart showing the change of spectral shift with the length of the sensing optical fiber 102 when the strain is 8000με; Curve N9 is a curve chart showing the change of spectral shift with the length of the sensing optical fiber 102 when the strain is 9000με; Curve N10 is a curve chart showing the change of spectral shift with the length of the sensing optical fiber 102 when the strain is 10000με. Compared with the curve of the spectral shift measured with the length of the sensing optical fiber 102 in the prior art, the curve of N1-N10 measured by the measurement method and measurement system provided in the embodiment of the present application can clearly see the curve of the spectral shift changing with the length of the sensing optical fiber 102.

[0101] It is easy to understand that those skilled in the art can combine, split, reorganize, etc. the embodiments of the present application to obtain other embodiments based on the several embodiments provided in the present application, and these embodiments do not exceed the protection scope of the present application.

[0102] The above specific implementation methods further explain in detail the purpose, technical solutions and beneficial effects of the embodiments of the present application. It should be understood that the above are only specific implementation methods of the embodiments of the present application and are not used to limit the protection scope of the embodiments of the present application. Any modifications, equivalent substitutions, improvements, etc. made on the basis of the technical solutions of the embodiments of the present application should be included in the protection scope of the embodiments of the present application.

Claims

1. An OFDR measurement method based on correlation spectrum self-compensation, characterized in that: The following steps are involved: Collecting a reference signal and a measurement signal; wherein the reference signal is frequency domain data that does not contain strain information, and the measurement signal is frequency domain data that contains strain information; The frequency domain data of the reference signal and the frequency domain data of the measurement signal are converted into distance domain data by using fast Fourier transform, and the spatial resolution length of the reference signal and the spatial resolution length of the measurement signal are calculated respectively; Dividing the distance domain data of the reference signal and the distance domain data of the measurement signal into sliding windows based on a preset spatial resolution, and performing an inverse fast Fourier transform on the data in each window to convert it into frequency domain data; While keeping the number of measurement points of the preset spatial resolution unchanged, the spectrum of the reference signal is moved in sequence in a wide frequency domain by means of the reference signal self-compensation, and cross-correlation calculations are performed with the measurement signal to obtain cross-correlation array results, thereby searching for the reference signal spectrum position with the highest correlation with the measurement signal, so that the spectrum of the reference signal and the spectrum of the measurement signal are matched within a wide strain range; The frequency spectrum offset between the reference signal and the measurement signal is calculated by a cross-correlation algorithm, and the strain distribution along the optical fiber is obtained by demodulation.

2. The OFDR measurement method based on correlation spectrum self-compensation according to claim 1, characterized in that: The preset spatial resolution The width satisfies the following formula: ， in, express The number of Rayleigh scattering points in represents the speed of light, represents the refractive index of the optical fiber, Indicates the frequency tuning range of the tunable laser source.

3. The OFDR measurement method based on correlation spectrum self-compensation according to claim 1, characterized in that: The cross-correlation algorithm comprises the following steps: Performing complex conjugate multiplication of the frequency domain data of the reference signal and the frequency domain data of the measurement signal; Perform inverse Fourier transform on the product result to generate a cross-correlation function sequence; The spectrum shift is determined by locating the peak of the cross-correlation function and eliminating multi-peak interference.

4. An OFDR measurement system based on correlation spectrum self-compensation, characterized in that: An OFDR measurement method based on correlation spectrum self-compensation according to any one of claims 1 to 3 is adopted, wherein the system comprises a tunable laser source and a sensing optical fiber, wherein the tunable laser source is configured to inject detection light into the sensing optical fiber; The system is configured to perform the following steps: Injecting detection light into the sensing optical fiber through the tunable laser source, and collecting frequency domain data of the reference signal under a strain-free condition and collecting frequency domain data of the measurement signal under a strain-existing condition; The frequency domain data of the reference signal and the frequency domain data of the measurement signal are converted into distance domain data by using fast Fourier transform, and the spatial resolution length of the reference signal and the spatial resolution length of the measurement signal are calculated respectively; Dividing the distance domain data of the reference signal and the distance domain data of the measurement signal into sliding windows based on a preset spatial resolution, and performing an inverse fast Fourier transform on the data in each window to convert it into frequency domain data; While keeping the number of measurement points of the preset spatial resolution unchanged, the spectrum of the reference signal is moved in sequence in a wide frequency domain by means of the reference signal self-compensation, and cross-correlation calculations are performed with the measurement signal to obtain cross-correlation array results, thereby searching for the reference signal spectrum position with the highest correlation with the measurement signal, so that the spectrum of the reference signal and the spectrum of the measurement signal are matched within a wide strain range; The frequency spectrum offset between the reference signal and the measurement signal is calculated by a cross-correlation algorithm, and the strain distribution along the optical fiber is obtained by demodulation.

5. The OFDR measurement system based on correlation spectrum self-compensation according to claim 4, characterized in that: The system further comprises: a first coupler, a second coupler, a third coupler, a Mach-Zehnder interferometer, a circulator, a first polarization controller, a polarization beam splitter, a second polarization controller and a data acquisition card; The output end of the tunable laser source is connected to the input end of the first coupler, the first output end of the first coupler is connected to the input end of the Mach-Zehnder interferometer, and the second output end of the first coupler is connected to the input end of the second coupler; the output end of the Mach-Zehnder interferometer is connected to the first input end of the data acquisition card; the first output end of the second coupler is connected to the first input end of the third coupler through the first polarization controller, and the second output end of the second coupler is connected to the first input end of the circulator; the output end of the third coupler is connected to the input end of the polarization beam splitter, and the second input end of the third coupler is connected to the first output end of the circulator; the p end and the s end of the polarization beam splitter output are respectively connected to the second input end and the third input end of the data acquisition card; the second output end of the circulator is connected to the sensing optical fiber through the second polarization controller.

6. The OFDR measurement system based on correlation spectrum self-compensation according to claim 4, characterized in that: The frequency modulation range of the tunable laser source The wavelength of the tunable laser source is 1510 nm to 1610 nm, and the line width of the tunable laser source is 100 MHz.

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