Long-distance fiber-optic sensitive ring multi-parameter high-precision decoupling method

Abstract

This invention provides a high-precision decoupling method for multiple parameters of long-distance fiber optic sensing loops, belonging to the fields of optical measurement and fiber optic sensing technology. Its key features include: using a polarization-maintaining OFDR to test the fast-axis and slow-axis signals of the fiber optic sensing loop before and after temperature changes; calculating the cross-correlation wavelength shift and autocorrelation wavelength shift; correcting positional deviations and decoupling coefficient fluctuations; obtaining the temperature and thermal strain distribution within the fiber optic sensing loop through decoupling; and using a strain and temperature calibration device on the fiber optic sensing loop pigtail to ensure the accuracy of the temperature and thermal strain decoupling results. This method can achieve high-precision (±0.5℃, ±5με) testing of the internal temperature and thermal strain distribution of kilometer-scale fiber optic sensing loops under rapid temperature changes, and can be used for multi-parameter detection, symmetry analysis, and performance prediction and optimization of gyroscope systems for fiber optic sensing loops.

Description

Technical fields:

[0001] This patented method belongs to the field of optical measurement and fiber optic sensing technology, specifically involving a high-precision decoupling method for multiple parameters of a long-distance fiber optic sensing loop. Background technology:

[0002] The fiber optic sensing loop, made of polarization-maintaining fiber wound in a specific manner, serves as the "brain" of fiber optic gyroscope technology, sensing changes in external attitude. Fiber optic gyroscope technology is a guidance and control technology based on the Sagnac effect, using angular velocity sensors to acquire velocity, attitude, and angle information. Currently, fiber optic gyroscopes have largely replaced traditional mechanical gyroscopes as the primary instruments in inertial measurement and guidance. Compared to mechanical gyroscopes, they offer advantages such as high precision, low cost, resistance to electromagnetic interference, long lifespan, and small size, holding a crucial position and possessing immense application value in aerospace, military, and sensing fields.

[0003] The fiber optic sensing loop is a key component of a fiber optic gyroscope system, and its performance directly determines the gyroscope's accuracy. During actual operation, internal heat generation and changes in ambient temperature applied to a section of fiber within the sensing loop cause temperature disturbances, inevitably resulting in a non-reciprocal phase shift. This non-reciprocal phase shift is indistinguishable from the phase shift caused by rotational attitude, leading to significant drift errors and affecting the gyroscope's output accuracy. Furthermore, in recent years, to improve gyroscope accuracy and dynamic range to meet the demands of long-duration navigation, the fiber optic cable length used in sensing loops has gradually decreased from 125μm to 60μm. This has significantly increased the winding length of the sensing loop within the same dimensions, making 3km-class fiber optic sensing loops the market mainstream. Therefore, high-precision temperature and thermal strain decoupling of long-distance fiber optic sensing loops is crucial for evaluating fiber optic gyroscope performance.

[0004] Currently, testing of fiber optic sensing rings primarily focuses on temperature variation. For example, Liu Yuanyuan and Yu Haicheng et al. from Beijing Aerospace Times Optoelectronics Technology Co., Ltd. proposed a fiber optic gyroscope fiber optic ring temperature testing and evaluation system (CN202010599862.6), which performs isothermal tests on the fiber optic ring at different temperature points. Using a large amount of temperature test results, they analyze the linear error based on the Shupe coefficient and the nonlinear error after linear compensation to evaluate the fiber optic ring. Therefore, the simultaneous testing and decoupling of temperature and thermal strain of fiber optic sensing rings has attracted widespread attention from researchers. For example, Wen Kunhua and Wang Huajuan et al. from Guangdong University of Technology proposed a distributed high-precision strain measurement method for fiber optic sensing rings under temperature variation conditions (CN202211009570.8). This method uses DTS to obtain distributed temperature information of the fiber optic sensing ring and Brillouin frequency shift results using BOTDA, then compensates for stress distribution using the distributed temperature information. However, this invention is limited by the spatial resolution of the Brillouin distributed sensing, and cannot obtain sufficiently detailed spatial results.

[0005] Many research techniques exist for temperature-strain decoupling in polarization-maintaining optical fibers. For example, Lu Yuting and Zhang Naiping et al. from the Central China Branch of State Grid Corporation of China and Yangtze Optical Fibre and Cable Joint Stock Limited Company proposed a fiber optic Brillouin distributed temperature and strain decoupling device and method based on an ANN algorithm (CN202211709927.3). This method acquires the Brillouin gain spectrum of the fiber under test by integrating OTDR and BOTDR data acquisition modules, and inputs it into an artificial neural network pre-trained under different temperatures and stresses to decouple the temperature and strain results. However, this invention performs relatively poorly for untrained temperature points and strain values, and the training results are only adapted to the parameters of the same type of fiber. Furthermore, different types of fibers will exhibit significant errors due to differences in parameters. Tu Guojie, Cao Lei, and others from Anhui University proposed an absolute temperature / stress measurement method based on phase OFDR (CN202410401966.X). This method improves a dual-path OFDR structure to obtain the fast-axis and slow-axis optical phases, differentially obtains the dual-axis phase, and splices it with the fast-axis phase. The absolute temperature / stress value is then determined based on the temperature-strain calculation coefficient. However, this invention is limited by phase noise, resulting in some splicing errors and problems with a short demodulation range and large demodulation error. Mark E. Froggatt proposed a method for identifying distributed strain and temperature in polarization-maintaining fibers (US11808260). By analyzing the fast-axis and slow-axis scattering data of polarization-maintaining fibers, the temperature and strain of the fiber can be distinguished. However, this invention only decouples the polarization-maintaining fiber and does not consider the accuracy degradation caused by the winding stress of fiber loops and other winding materials, or by fiber length misalignment. Xue Yuanze, Wang Xuefeng, and others from the Beijing Institute of Aeronautics and Astronautics Control Devices proposed a position deviation compensation algorithm based on maximum cross-correlation (doi:10.1364 / AO.442248). This algorithm compares the correlation of windows within a certain step size, recording the window with the strongest correlation as the compensated window, thus simultaneously compensating for position deviations caused by temperature or strain changes in the fiber under test and the auxiliary interferometer. However, this correction scheme traverses all nearby windows, resulting in high algorithm time and hardware overhead, making it unsuitable for long-distance fiber position deviation correction. He Zuyuan and others from Shanghai Jiao Tong University proposed a centimeter-level spatial resolution DTS system based on polarization-sensitive OFDR (doi:10.1109 / JLT.2021.3052036). This system demodulates the birefringence distribution along the fiber direction by calculating the Rayleigh backscattering spectral difference between the fast and slow axes, and then demodulates the absolute temperature information through the relationship between absolute temperature and birefringence. However, the temperature measurement uncertainty of this scheme is affected by the inhomogeneity of the birefringence in the polarization-maintaining fiber and is also limited by random noise. Furthermore, it cannot simultaneously decouple temperature and strain.Li Wenhai et al. from the University of Ottawa proposed a polarization-sensitive optical frequency domain reflectometer to simultaneously measure temperature and strain. They calculated the temperature and strain coefficients of the polarization-maintaining fiber by performing autocorrelation and cross-correlation calculations on the spectrum, forming a distributed parameter matrix to compensate for measurement errors. However, this scheme does not consider the accuracy degradation that may occur in kilometer-scale fiber demodulation due to positional deviations caused by temperature or strain in the fiber.

[0006] In addition, there are optical fibers, methods, and devices (US15525306) proposed by LUNA Corporation in the United States for precise optical fiber measurement under various stimuli, which utilize the characteristic that different cores of multi-core optical fibers have different temperature / strain changes to decouple temperature and strain. Furthermore, Mao Yan, Tong Xinglin, and others from the Weihai Research Institute of Wuhan University of Technology proposed a temperature and strain monitoring system and method based on a dual-core weak-reflection FBG array with different doping (CN202111297771.8), which utilizes the characteristic that different doped fiber cores have different temperature / strain sensitivity coefficients to achieve temperature and strain decoupling. These schemes improve and optimize the sensing optical fiber, decoupling temperature and strain through the principle that different optical fibers have different temperature and strain changes; however, these methods are not applicable to the testing of optical fiber sensing loops. Summary of the Invention:

[0007] The purpose of this invention is to provide a high-precision decoupling method for multiple parameters of long-distance fiber optic sensing rings. In the temperature change test of fiber optic sensing rings, this method eliminates the influence of intrinsic decoupling coefficient fluctuations caused by winding stress and demodulation accuracy degradation caused by fiber length misalignment on the measurement, thereby achieving high-precision temperature and thermal strain decoupling of long-distance fiber optic sensing rings.

[0008] This invention proposes a high-precision decoupling method for multiple parameters of a long-distance optical fiber sensing loop, characterized by the following steps:

[0009] Step S1: Set up the fiber optic sensitive loop test system and calibrate the fiber optic module;

[0010] Step S2: Perform fiber optic sensitive loop testing to obtain the reference fast axis signal, reference slow axis signal, test fast axis signal, and test slow axis signal;

[0011] Step S3: By correcting the positional deviation, obtain the corrected cross-correlation wavelength offset and the difference between the autocorrelation wavelength offset. The specific process is as follows:

[0012] Step 301: Perform Fourier transform on the reference fast axis signal, the reference slow axis signal, the test fast axis signal, and the test slow axis signal to obtain the scattering spectrum of the reference fast axis signal, the scattering spectrum of the reference slow axis signal, the scattering spectrum of the test fast axis signal, and the scattering spectrum of the test slow axis signal;

[0013] Step 302: Divide the reference fast-axis signal scattering spectrum, the reference slow-axis signal scattering spectrum, the test fast-axis signal scattering spectrum, and the test slow-axis signal scattering spectrum into N segments, where N is the ratio of the scattering spectrum data length to the test spatial resolution. Each segment of the scattering spectrum of different signals corresponds one-to-one.

[0014] Step 303: Correct the positional deviation of the reference fast-axis signal scattering spectrum and the test fast-axis signal scattering spectrum;

[0015] Step 304: Based on step 303, the position deviation of the reference fast axis signal scattering spectrum and the reference slow axis signal scattering spectrum is corrected to obtain the position deviation distribution of the reference slow axis signal scattering spectrum relative to the reference fast axis signal, and the reference slow axis signal scattering spectrum is interpolated based on the distribution to obtain the corrected reference slow axis signal scattering spectrum.

[0016] Step 305: Based on step 303, the position deviation of the test fast axis signal scattering spectrum and the test slow axis signal scattering spectrum is corrected to obtain the position deviation distribution of the test slow axis signal scattering spectrum relative to the test fast axis signal, and the test slow axis signal scattering spectrum is interpolated based on the distribution to obtain the corrected test slow axis signal scattering spectrum.

[0017] Step 306: Perform correlation demodulation on the reference fast-axis signal and the corrected test fast-axis signal to obtain the cross-correlation wavelength offset v. c The reference fast-axis signal and the corrected reference slow-axis signal are correlated and demodulated to obtain the reference autocorrelation wavelength offset; the test fast-axis signal and the corrected test slow-axis signal are correlated and demodulated to obtain the test autocorrelation wavelength offset.

[0018] Step 307: Based on the recorded distribution of the deviation of the reference test position, interpolate the test autocorrelation wavelength offset to obtain the corrected test autocorrelation wavelength offset.

[0019] Step 308: Subtract the corrected reference autocorrelation wavelength offset from the test autocorrelation wavelength offset to obtain the autocorrelation wavelength offset difference;

[0020] Step S4: Obtain the cross-correlation wavelength shift and the difference between the corrected autocorrelation wavelength shift by correcting the decoupling coefficient;

[0021] Step S5: Substitute the decoupling formula to obtain the actual temperature strain result, and judge the decoupling result against the calibration fiber. If the decoupling result of the calibration fiber meets the requirements, it proves that the demodulation result is correct; otherwise, return to step S3 for correction.

[0022] Step S1 consists of the following steps:

[0023] Select a fiber optic sensing ring 201 to be tested, and fuse a certain length of extended polarization-maintaining fiber 202 to the output pigtail 201a of the fiber optic sensing ring 201 to be tested. The fiber optic sensing ring 201 to be tested, its output pigtail 201a, and its input pigtail 201b are all polarization-maintaining fibers.

[0024] A strain calibration device was set up, and a certain length of the extended polarization-maintaining fiber 202 was selected as the strain calibration section fiber 202a. It was bonded to the fiber strain tension table 22 and fixed, and a fixed strain was applied. It was then placed inside the rapid temperature control test chamber 23.

[0025] A temperature calibration device was set up. The part of the extended polarization-maintaining fiber 202 that was not on the fiber strain tension table was selected as the temperature calibration section fiber 202b. The temperature calibration section fiber was placed in a relaxed state inside the rapid temperature control test chamber 23 without any additional stress applied.

[0026] Connect the test system, place the fiber optic sensing ring 201 under test in the rapid temperature control test chamber 23, and connect the fiber optic sensing ring 201 under test to the optical frequency domain reflectance (OFDR) test system 21 via the pigtail 201b.

[0027] Step S2 consists of the following steps:

[0028] To conduct the first test, the Optical Frequency Domain Reflectometry (OFDR) test system 21 was started to acquire the first distributed fast axis and slow axis signals. The first distributed fast axis signal was used as the reference fast axis signal, and the first distributed slow axis signal was used as the reference slow axis signal.

[0029] After setting the temperature excitation, start the rapid temperature control test chamber 23. After the temperature stabilizes, start the optical frequency domain reflectance (OFDR) test system 21 to acquire the second distributed fast axis and slow axis signals. Use the obtained second distributed fast axis signal as the test fast axis signal and the obtained second distributed slow axis signal as the test slow axis signal.

[0030] Step 303 consists of the following steps:

[0031] The correlation between the reference fast-axis signal scattering spectrum and the test fast-axis signal scattering spectrum at corresponding positions is calculated to obtain the correlation spectrum corresponding to each segment of the reference fast-axis signal scattering spectrum and the test fast-axis signal scattering spectrum. One segment of the correlation spectrum is taken and denoted as the x-th segment of the correlation spectrum. The positions of the maximum correlation spectrum amplitude l1(x) and l2(x) are obtained. Subtracting these two positions yields the position deviation l of the test fast-axis signal scattering spectrum relative to the reference fast-axis signal scattering spectrum at the x-th segment. p (x) = l2(x) - l1(x), and based on the position deviation of each segment, fit the position deviation distribution of the test fast axis signal scattering spectrum relative to the reference fast axis signal, denoted as the reference test position deviation distribution.

[0032] Step S4 consists of the following steps:

[0033] Step 401: Take the derivative of the reference autocorrelation wavelength offset B(s,T) after position deviation correction and add one to it, and use it as the decoupling coefficient correction form;

[0034] Step 402: Adjust the autocorrelation wavelength shift difference v using the decoupling coefficient. a-old After correction, the autocorrelation wavelength shift difference after decoupling coefficient correction is obtained. The correction formula is as follows:

[0035] v a =v a-old ·[B′(s,T)+1].

[0036] Step S5 consists of the following steps:

[0037] The autocorrelation wavelength shift difference v a Cross-correlation wavelength offset v c The autocorrelation temperature coefficient T of the fiber used in the step and polarization-maintaining fiber ring a Autocorrelation strain coefficient T c Cross-correlation temperature coefficient ε a Cross-correlation strain coefficient ε c Substituting into the decoupling formula, the temperature decoupling result ΔT and the thermal strain decoupling result Δε are calculated. The decoupling formula is as follows:

[0038]

[0039] The obtained decoupling results are judged to determine whether they meet the following requirements: the strain value obtained from the strain decoupling result at the strain calibration section fiber 202a is the same as the strain applied by the fiber strain tension table 22, and the temperature change obtained from the temperature decoupling result is the same as the temperature excitation set by the rapid temperature control test chamber 23; and the strain value obtained from the strain decoupling result at the temperature calibration section fiber 202b is 0, and the temperature change obtained from the temperature decoupling result is the same as the temperature excitation set by the rapid temperature control test chamber 23. If the decoupling results meet the requirements, it is proven that the decoupling results are correct; otherwise, return to step S3 to correct them again.

[0040] Compared with the prior art, the advantages of the present invention are as follows:

[0041] 1. This invention can achieve temperature and thermal strain decoupling of the fiber optic sensing ring under rapid temperature changes.

[0042] 2. This invention extends the decoupling distance to the kilometer level by correcting position deviation, enabling long-distance fiber optic sensitive loop testing.

[0043] 3. This invention improves decoupling accuracy by correcting the decoupling coefficient, achieving a temperature decoupling accuracy of ±0.5℃ and a strain decoupling accuracy of ±5με.

[0044] 4. By adopting a calibration device, the accuracy of the temperature and strain decoupling results is ensured. The distributed temperature and thermal strain results of the fiber optic sensing ring can be obtained simultaneously in one scan. The test efficiency is high and the stability is good. It can be used for performance prediction, symmetry optimization, quality evaluation and screening of fiber optic sensing rings, as well as the development of high-performance multi-parameter sensors. Attached image description:

[0045] Figure 1 This is a flowchart of a high-precision decoupling method for multiple parameters of long-distance fiber optic sensing loops.

[0046] Figure 2 This is a structural diagram of a long-distance fiber optic sensing loop multi-parameter testing device.

[0047] Figure 3 This is a flowchart of position deviation correction and decoupling coefficient correction.

[0048] Figure 4 This is a comparison chart of the reference slow-axis signal scattering spectrum and the test slow-axis signal scattering spectrum before and after position deviation correction.

[0049] Figure 5 This is a graph showing the demodulation results of cross-correlation wavelength offset.

[0050] Figure 6 This is a demodulation result of the reference autocorrelation wavelength offset and the test autocorrelation wavelength offset after position deviation correction.

[0051] Figure 7 This is a comparison chart of the autocorrelation wavelength shift difference before and after correction by the decoupling coefficient.

[0052] Figure 8 This is a diagram showing the decoupling results of temperature and thermal strain in the extended polarization-maintaining fiber section.

[0053] Figure 9 This is a diagram showing the temperature decoupling results of the fiber optic sensing ring.

[0054] Figure 10 This is a diagram showing the results of thermal strain decoupling of the fiber optic sensitive ring. Detailed implementation method:

[0055] To clearly illustrate the high-precision decoupling method for multiple parameters of a long-distance fiber optic sensing loop according to the present invention, the present invention will be further described in conjunction with embodiments and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0056] Building such Figure 2The fiber optic sensing loop testing device shown illustrates a high-precision decoupling process for multiple parameters in long-distance fiber optic sensing loops, as follows: Figure 1 As shown:

[0057] Select a fiber optic sensing loop with a fiber length of approximately 3km, and fusion splice the polarization-maintaining fiber at the end of the output pigtail of the sensing loop to extend the fiber length to 12 meters.

[0058] A 0.5-meter-long fiber was selected as the strain calibration section fiber at a distance of 3 meters from the splice point of the extended polarization-maintaining fiber and the output pigtail of the fiber sensitive ring. The fiber was fixed on the fiber strain tension table with a tensile length of 60 micrometers, i.e. 120 microstrain. The fiber strain tension table was placed inside the rapid temperature control test chamber.

[0059] The entire extended polarization-maintaining fiber is used as the temperature calibration section fiber, and the part of the temperature calibration section fiber that is not on the fiber strain tension table is placed in a relaxed state inside the rapid temperature control test chamber. That is, no additional stress is applied to the part of the temperature calibration section fiber that is not on the fiber strain tension table inside the rapid temperature control test chamber.

[0060] Place the fiber optic sensing ring to be tested inside a rapid temperature control test chamber;

[0061] Start the optical frequency domain reflectance (OFDR) test system, record the first distributed fast axis result as the reference fast axis result, and record the first distributed slow axis result as the reference slow axis result;

[0062] Start the rapid temperature control test chamber, set the heating rate to 2 degrees Celsius per minute, hold the temperature for 1 minute after heating, and start the optical frequency domain reflectance (OFDR) test system after the temperature stabilizes. Record the second distributed fast axis result as the test fast axis result and the second distributed slow axis result as the reference slow axis result.

[0063] Position deviation correction and decoupling coefficient correction are performed by referencing the fast axis signal, the slow axis signal, the test fast axis signal, and the test slow axis signal. The correction process is as follows: Figure 3 As shown:

[0064] First, perform Fourier transform on the reference fast-axis signal, the reference slow-axis signal, the test fast-axis signal, and the test slow-axis signal to obtain the scattering spectrum of the reference fast-axis signal, the scattering spectrum of the reference slow-axis signal, the scattering spectrum of the test fast-axis signal, and the scattering spectrum of the test slow-axis signal.

[0065] The scattering spectra of the reference fast-axis signal, the reference slow-axis signal, the test fast-axis signal, and the test slow-axis signal are all divided into N segments (N is the data length / test spatial resolution).

[0066] Calculate the correlation between the scattering spectra of the reference fast axis signal and the test fast axis signal for each segment. Take the position corresponding to the maximum correlation and the position corresponding to the minimum correlation, and subtract the two to obtain the position deviation of the signal. The position deviation distribution between the scattering spectra of the reference fast axis signal and the test fast axis signal is obtained through the position deviation results of each segment, and is denoted as the reference-test position deviation distribution.

[0067] The reference fast-axis signal scattering spectrum and the reference slow-axis signal scattering spectrum are processed according to the above method to obtain the positional deviation distribution between the reference fast-axis signal scattering spectrum and the reference slow-axis signal scattering spectrum, and polynomial interpolation is performed on the reference slow-axis signal based on this distribution.

[0068] The scattering spectra of the fast-axis test signal and the slow-axis test signal are processed according to the above method to obtain the positional deviation distribution between the scattering spectra of the fast-axis test signal and the slow-axis test signal, and polynomial interpolation is performed on the slow-axis test signal based on this distribution.

[0069] Comparison of reference slow axis signal and test slow axis signal position before and after correction, as shown below Figure 4 As shown;

[0070] The OFDR correlation demodulation method was used to demodulate the scattering spectra of the reference fast-axis signal and the test fast-axis signal to obtain the cross-correlation wavelength shift, such as... Figure 5 As shown;

[0071] The OFDR correlation demodulation method was used to demodulate the scattering spectrum of the reference fast-axis signal and the scattering spectrum of the reference slow-axis signal after position deviation correction to obtain the reference autocorrelation wavelength shift. Similarly, the scattering spectrum of the test fast-axis signal and the scattering spectrum of the test slow-axis signal after position deviation correction were demodulated to obtain the test autocorrelation wavelength shift. The recorded reference test position deviation distribution was then used to correct the position deviation of both the reference and test autocorrelation wavelength shifts, resulting in the position deviation-corrected reference and test autocorrelation wavelength shifts, as shown below. Figure 6 As shown;

[0072] Subtracting the corrected reference autocorrelation wavelength offset from the measured autocorrelation wavelength offset yields the autocorrelation wavelength offset difference v. a-old ;

[0073] Further, take the reference autocorrelation wavelength offset B(s,T), differentiate it, add 1, and denote it as the modified form of the decoupling coefficient. Then, take the autocorrelation wavelength offset difference v. a-old Substituting into the following formula, we obtain the autocorrelation wavelength shift difference v after decoupling coefficient correction. a ;

[0074] v a =v a-old·[B′(s,T)+1]

[0075] A comparison of the difference in autocorrelation wavelength shift before and after decoupling coefficient correction is shown below. Figure 7 As shown

[0076] The autocorrelation temperature coefficient T of the fiber used in the polarization-maintaining fiber loop will be measured. a Autocorrelation strain coefficient T c Cross-correlation temperature coefficient ε a Cross-correlation strain coefficient ε c and the autocorrelation wavelength shift difference v a and cross-correlation wavelength offset v c Substituting into the decoupling formula, we obtain the temperature decoupling result ΔT and the thermal strain decoupling result Δε. The decoupling formula is as follows:

[0077]

[0078] The temperature decoupling result ΔT and the thermal strain decoupling result Δε of the extended polarization-maintaining fiber section are evaluated. The temperature and thermal strain decoupling results of the extended polarization-maintaining fiber section are as follows: Figure 8 As shown, when the thermal strain decoupling result shows a strain value of 120 microstrain only in the strain calibration section of the fiber, and the temperature decoupling result shows a temperature of 2 degrees Celsius in the temperature calibration section of the fiber, the decoupling result is considered correct. The fiber optic sensing ring temperature decoupling result is shown below. Figure 9 The results of thermal strain decoupling are shown below. Figure 10 As shown, temperature and thermal strain decoupling was achieved for a 3km long-distance fiber optic sensing loop, with a temperature decoupling accuracy of ±0.5℃ and a strain decoupling accuracy of ±5με.

Claims

1. A high-precision decoupling method for multiple parameters in a long-distance fiber optic sensing loop, characterized by: The method consists of the following steps: 1) Step S1: Build the fiber optic sensitive loop test system and calibrate the fiber optic module; 2) Step S2: Perform fiber optic sensitive loop testing to obtain reference fast axis signal, reference slow axis signal, test fast axis signal, and test slow axis signal; 3) Step S3: By correcting the positional deviation, obtain the corrected cross-correlation wavelength offset and the difference between the autocorrelation wavelength offset. The specific process is as follows: Step (301): Perform Fourier transform on the reference fast axis signal, the reference slow axis signal, the test fast axis signal, and the test slow axis signal to obtain the scattering spectrum of the reference fast axis signal, the scattering spectrum of the reference slow axis signal, the scattering spectrum of the test fast axis signal, and the scattering spectrum of the test slow axis signal; Step (302): Divide the reference fast-axis signal scattering spectrum, the reference slow-axis signal scattering spectrum, the test fast-axis signal scattering spectrum, and the test slow-axis signal scattering spectrum into N segments, where N is the ratio of the scattering spectrum data length to the test spatial resolution used. Each segment of the scattering spectrum of different signals corresponds one-to-one. Step (303): Correct the positional deviation of the reference fast-axis signal scattering spectrum and the test fast-axis signal scattering spectrum; Step (304): According to step (303), the position deviation of the reference fast axis signal scattering spectrum and the reference slow axis signal scattering spectrum is corrected to obtain the position deviation distribution of the reference slow axis signal scattering spectrum relative to the reference fast axis signal, and the reference slow axis signal scattering spectrum is interpolated according to the distribution to obtain the corrected reference slow axis signal scattering spectrum. Step (305): According to step (303), the position deviation of the test fast axis signal scattering spectrum and the test slow axis signal scattering spectrum is corrected to obtain the position deviation distribution of the test slow axis signal scattering spectrum relative to the test fast axis signal, and the test slow axis signal scattering spectrum is interpolated according to the distribution to obtain the corrected test slow axis signal scattering spectrum. Step (306): Perform correlation demodulation on the reference fast axis signal and the corrected test fast axis signal to obtain the cross-correlation wavelength offset; The reference fast-axis signal and the corrected reference slow-axis signal are correlated and demodulated to obtain the reference autocorrelation wavelength offset. The fast-axis test signal and the corrected slow-axis test signal are correlated and demodulated to obtain the test autocorrelation wavelength offset. Step (307): Based on the recorded distribution of the deviation of the reference test position, interpolate the test autocorrelation wavelength offset to obtain the corrected test autocorrelation wavelength offset. Step (308): Subtract the corrected reference autocorrelation wavelength offset from the test autocorrelation wavelength offset to obtain the autocorrelation wavelength offset difference; 4) Step S4: Obtain the cross-correlation wavelength shift and the difference between the corrected autocorrelation wavelength shift by correcting the decoupling coefficient; 5) Step S5: Substitute into the decoupling formula to obtain the actual temperature strain result, and judge the decoupling result with the calibration fiber. If the decoupling result of the calibration fiber meets the requirements, it proves that the demodulation result is correct; otherwise, return to step S3 for correction.

2. The high-precision decoupling method for multiple parameters of a long-distance fiber optic sensing loop as described in claim 1, characterized in that: Step S1 consists of the following steps: 1) Select a fiber optic sensing ring (201) to be tested, and fuse a certain length of extended polarization-maintaining fiber (202) to the output pigtail (201a) of the fiber optic sensing ring (201). The fiber optic sensing ring (201), its output pigtail (201a) and its input pigtail (201b) are all polarization-maintaining fibers. 2) Build a strain calibration device, select a certain length of the extended polarization-maintaining fiber (202) as the strain calibration section fiber (202a), bond it to the fiber strain tension table (22) and apply a fixed strain, and place it inside the rapid temperature control test chamber (23). 3) Set up a temperature calibration device, select the part of the extended polarization-maintaining fiber (202) that is not on the fiber strain tension table as the temperature calibration section fiber (202b), and place the temperature calibration section fiber in a relaxed state inside the rapid temperature control test chamber (23) without applying additional stress. 4) Connect the test system, place the fiber optic sensing ring (201) under test in the rapid temperature control test chamber (23), and connect the fiber optic sensing ring (201) under test to the optical frequency domain reflectance (OFDR) test system (21) via the input pigtail (201b).

3. The high-precision decoupling method for multiple parameters of a long-distance fiber optic sensing loop as described in claim 1, characterized in that: Step S2 consists of the following steps: 1) Conduct the first test, start the optical frequency domain reflectance (OFDR) test system (21), obtain the first distributed fast axis and slow axis signals, use the obtained first distributed fast axis signal as the reference fast axis signal, and use the obtained first distributed slow axis signal as the reference slow axis signal; 2) After setting the temperature excitation, start the rapid temperature control test chamber (23). After the temperature stabilizes, start the optical frequency domain reflectance (OFDR) test system (21) to obtain the second distributed fast axis and slow axis signals. Use the obtained second distributed fast axis signal as the test fast axis signal and the obtained second distributed slow axis signal as the test slow axis signal.

4. The high-precision decoupling method for multiple parameters of a long-distance optical fiber sensing loop as described in claim 1, characterized in that: The step (303) consists of the following steps: The correlation between the reference fast-axis signal scattering spectrum and the test fast-axis signal scattering spectrum at corresponding positions is calculated to obtain the correlation spectrum corresponding to each segment of the reference fast-axis signal scattering spectrum and the test fast-axis signal scattering spectrum. One segment of the correlation spectrum is taken and denoted as the x-th segment of the correlation spectrum. The positions of the maximum correlation spectrum amplitude l1(x) and l2(x) are obtained. Subtracting these two positions yields the position deviation l of the test fast-axis signal scattering spectrum relative to the reference fast-axis signal scattering spectrum at the x-th segment. p (x) = l2(x) - l1(x), and based on the position deviation of each segment, fit the position deviation distribution of the test fast axis signal scattering spectrum relative to the reference fast axis signal, denoted as the reference test position deviation distribution.

5. A high-precision decoupling method for multiple parameters of a long-distance fiber optic sensing loop as described in claim 1, characterized in that: Step S4 consists of the following steps: 1) Step (401): Take the derivative of the reference autocorrelation wavelength offset B(s,T) after position deviation correction and add one to it, and use it as the decoupling coefficient correction form; 2) Step (402): Correct the autocorrelation wavelength shift difference v using the decoupling coefficient. a-old After correction, the autocorrelation wavelength shift difference v after decoupling coefficient correction is obtained. a The corrected formula is as follows: v a =v a-old ·[B′(s,T)+1]。 6. The high-precision decoupling method for multiple parameters of a long-distance optical fiber sensing loop as described in claim 1, characterized in that: Step S5 consists of the following steps: 1) The autocorrelation wavelength shift difference v a Cross-correlation wavelength offset v c The autocorrelation temperature coefficient T of the fiber used in the step and polarization-maintaining fiber ring a Autocorrelation strain coefficient T c Cross-correlation temperature coefficient ε a Cross-correlation strain coefficient ε c Substituting into the decoupling formula, the temperature decoupling result ΔT and the thermal strain decoupling result Δε are calculated. The decoupling formula is as follows: 2) Judge the obtained decoupling results to determine whether the strain value obtained by the strain decoupling result at the strain calibration section fiber (202a) is the same as the strain applied by the fiber strain tension table (22) and the temperature change obtained by the temperature decoupling result is the same as the temperature excitation set by the rapid temperature control test chamber (23). If the decoupling result meets the requirements, it proves that the decoupling result is correct; otherwise, return to step S3 to correct it again.

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