A method for measuring the physical symmetry of an optical fiber sensing ring under a temperature field

Abstract

This invention provides a method for measuring the physical symmetry of an optical fiber sensing ring, belonging to the fields of optical measurement and optical fiber sensing technology. The method includes: using polarization-maintaining OFDR and multi-parameter decoupling technology to measure the temperature change and thermal strain of the optical fiber ring at different temperatures; calculating the asymmetric refractive index distribution under temperature changes, and then calculating the correlation coefficient of a single layer / turn unit to evaluate the physical symmetry of that unit; accumulating the correlation coefficients of all units to obtain the equivalent correlation coefficient, and calculating the full-temperature equivalent correlation coefficient distribution at all temperature points to achieve the evaluation of physical symmetry. This invention can achieve quantitative evaluation of physical symmetry. Combined with high spatial resolution data, it can provide in-depth evaluation of the physical symmetry between optical fiber layers and turns, diagnose physical symmetry faults in optical fiber rings, and plays an important role in optimizing the winding process, quality evaluation, and improving the yield of optical fiber rings.

Description

Technical Field

[0001] This patented method belongs to the field of fiber optic gyroscope testing, specifically involving a method for testing the physical symmetry of a fiber optic sensing ring under a temperature field based on optical frequency domain reflection. Background Technology

[0002] Fiber optic gyroscopes are high-precision angular velocity measuring instruments based on the Sagnac effect, invented in the 1970s. However, the sensing ring in a fiber optic gyroscope is susceptible to environmental influences; for example, changes in external temperature can directly cause zero-point drift, severely limiting the improvement of gyroscope performance.

[0003] Physical symmetry, also known as optical symmetry or optical path symmetry, refers to the consistency between the midpoint of the optical path of the gyroscope's sensing ring and the midpoint of the actual length of the optical fiber. It directly affects the performance of the gyroscope's Mohr and Shupe effects. The influencing factors of physical symmetry mainly stem from the differences in material properties of the various components within the fiber ring and the asymmetry of their temperature responses. Compared to geometric symmetry, physical symmetry is the direct cause of thermally induced zero drift in fiber optic gyroscopes.

[0004] Optical frequency domain reflection (OFDR) technology was first proposed by Eickhoff in 1981. Since then, it has been widely studied and improved due to its advantages such as high spatial resolution and dynamic range. However, due to the mutual constraint between test length and sensing accuracy, it is impossible to achieve long-distance overall gyroscope optical path testing. For example, Yu Ting, Yan Zhibing, and others from Huaxing Xinrui Communication Technology Group Co., Ltd. published a method for locating and detecting the optical path center point of a thin-film fiber ring (CN106706001A). This method uses femtosecond laser etching of fiber gratings to etch fiber gratings near the approximate center point of the sensitive ring. Then, relying on optical frequency domain reflection technology, the optical path center point of the polarization-maintaining fiber sensitive ring is accurately located by precisely detecting the position of the fiber grating in the polarization-maintaining fiber sensitive ring. However, its use requires prior estimation of the total fiber length and midpoint before winding into a ring, making it impossible to directly test the physical symmetry of the gyroscope optical path or detect other defects inside the fiber sensitive ring.

[0005] In 2008, Yao Xiaotian et al. of Beijing Gaoguang Technology Co., Ltd. published a method and device for measuring the mass of fiber optic rings used in fiber optic gyroscopes (CN101339093B). This method obtains quantified information on the radial and axial equivalent asymmetries of the fiber optic ring winding by applying radial and axial temperature excitations to the fiber optic ring and combining the simulation results of the three-dimensional mathematical model of the fiber optic ring. However, due to limitations in the spatial resolution and strain accuracy of the testing instruments, high-precision measurement of the full-temperature physical symmetry of the fiber optic sensing ring under a temperature field is currently not possible. The low testing accuracy and the lack of correction of testing parameters based on information such as polarization crosstalk of the fiber optic sensing ring also lead to significant errors in the final test results.

[0006] In 2012, Suzhou Guanghuan Technology Co., Ltd. disclosed a method and apparatus for detecting the quality of fiber optic rings used in gyroscopes (CN103048115B). This method applies radial temperature excitation to the fiber optic ring under test, and determines the equivalent asymmetric length of the ring by measurement, thereby judging the quality of the fiber optic ring. However, due to limitations in its testing instruments and methods, it cannot achieve the accuracy of distributed characteristic parameters measured using a high-precision OFDR testing system. Furthermore, this method cannot quantitatively analyze the main influencing factor of gyroscope zero drift, namely the physical symmetry of the fiber optic sensitive ring.

[0007] In 2014, Yang Dongkun et al. from the 618 Research Institute of China Aviation Industry proposed a method for evaluating and compensating for the reciprocity symmetry of fiber optic rings (CN104296964B). This invention utilizes enhanced Brillouin back reflection detection technology to obtain stress state distribution data within the fiber optic ring that characterizes reciprocity symmetry. A symmetry model within the operating temperature range is established using this distribution data, and the reciprocity symmetry of the fiber optic ring under test is analyzed and evaluated. Based on the obtained optimal reciprocity symmetry position and the magnitude and direction of the error, the relationship between the actual geometric symmetry position and the optical symmetry position is adjusted to compensate for the error. However, this invention is limited by the spatial resolution and strain accuracy of the Brillouin back reflection detection technology, making it unable to perform high-precision detection of strain within the fiber optic ring, and the stress state distribution data has a relatively large error.

[0008] Beijing Zhongke Panhua Measurement & Control Technology Co., Ltd. has proposed a fiber optic gyroscope testing system and method (CN117191078A). This method places several fiber optic gyroscope groups on a test turntable inside a temperature chamber. The temperature chamber is adjusted according to a preset temperature curve, and the test turntable is adjusted according to a preset rotation speed, causing the fiber optic gyroscope groups to rotate. The output voltage value corresponding to the fiber optic gyroscope is acquired through a data acquisition board. The predicted output voltage value of the gyroscope system is compared with the actual output voltage value to obtain the judgment result of the fiber optic gyroscope group. This method is used to test the performance parameters of fiber optic gyroscopes in dynamic and static conditions at temperatures ranging from -55℃ to 80℃. However, this testing method can only screen the overall gyroscope system for compliance and cannot test internal parameters such as the symmetry of the fiber optic sensitive ring.

[0009] In 2019, the 707 Research Institute of China Shipbuilding Industry Corporation disclosed a method for testing and analyzing the scaling stability of fiber optic gyroscope ring components (CN109357690A). This method divides the fiber optic gyroscope into a ring component module (including the ring and Y waveguide) and an optoelectronic module (including the light source and circuitry). It largely eliminates the influencing factors other than the ring component in the fiber optic gyroscope to test the scaling stability of the gyroscope system. However, it is not suitable for the quantitative measurement of the physical symmetry of the gyroscope optical path under temperature field.

[0010] In 2017, the Tianjin Navigation Instrument Research Institute published a paper titled "The Express Test of Winding Symmetry Quality in Fiber Coils," which experimentally studied the symmetry characteristics of fiber optic gyroscope rings under periodically varying temperature excitation and introduced the equivalent asymmetry degree (EAD) to quantify the winding symmetry quality of the fiber coil. A rapid EAD measurement method was proposed, which can quickly detect the winding symmetry quality of the fiber optic gyroscope ring. However, the paper did not analyze in detail the physical symmetry of the gyroscope's optical path under temperature fields, nor did it distinguish the effects of physical symmetry and geometric symmetry on the gyroscope's zero-drift performance.

[0011] In 2021, Beijing Aerospace Times Optoelectronics Technology Co., Ltd. published a paper titled "An Evaluation Method for the Temperature Performance of Fiber Rings Based on Equivalent Asymmetric Length." According to the Shupe error mechanism, only when the equivalent midpoint coincides with the physical midpoint can the zero-bias errors caused by temperature on both sides of the equivalent midpoint be truly completely opposite. The paper proposes an evaluation method for fiber rings based on equivalent asymmetric length, quantitatively evaluating the symmetry of the fiber ring through its equivalent asymmetric length.

[0012] A 2023 paper published by the 16th Research Institute of China Aerospace Science and Technology Corporation, titled "Research on Precision Winding Technology," discovered that the symmetry of the fiber optic loop affects the temperature performance of fiber optic gyroscopes. Fiber optic loops with good symmetry also exhibit good temperature performance. The paper describes an OFDR-based fiber optic loop optical center detection method that can effectively detect the optical asymmetry of the fiber optic loop relative to its center point, but it does not detect the overall physical asymmetry of the gyroscope's optical path.

[0013] The aforementioned evaluation and testing methods are helpful in screening the symmetry of fiber optic rings under temperature fields, but they offer no guidance for improving the application of fiber optic gyroscopes. The symmetry of the fiber optic sensing ring under temperature fields reflects the overall performance of the fiber optic gyroscope. This parameter is influenced by multiple factors, including the winding method of the fiber optic sensing ring, the fiber winding state, and the strain distribution of the overall gyroscope optical path. It is not only a key factor determining the temperature performance of the fiber optic gyroscope, but the method described in this invention can accurately evaluate the physical symmetry of the gyroscope optical path under temperature fields, and also provides direct and effective guidance for improving and adjusting the gyroscope optical path. Summary of the Invention

[0014] A method for measuring the physical symmetry of an optical fiber sensing ring under a temperature field is disclosed. The method first requires the construction of a high-performance OFDR testing system to test the distributed characteristic parameters (temperature and strain) of the optical fiber sensing ring and calculate the refractive index variable of the winding. Subsequently, layer-turn symmetry analysis is performed. The method for measuring the symmetry of the optical fiber sensing ring under a temperature field is characterized by the following steps:

[0015] Step 101: First, the temperature field for testing the fiber optic sensitive loop needs to be configured to meet the temperature field testing conditions described in the method of this invention.

[0016] Step 2.102: Use a high-performance optical frequency domain reflection system to measure the distributed characteristic parameters of the fiber optic sensing loop located in the temperature field;

[0017] Step 3.103: Based on the testing requirements, select several representative specific temperature points within the temperature field for subsequent testing;

[0018] Step 4.104: Perform multi-parameter decoupling on the temperature and strain parameters in the distributed characteristic parameters obtained from the high-performance optical frequency domain reflection system test;

[0019] Step 5.105: Demodulate the distributed characteristic parameters to obtain the temperature change of the fiber optic sensing loop under the applied temperature field;

[0020] Step 6.106: Simultaneously, demodulating the parameters obtained from the high-performance OFDR test can yield the thermal strain of the fiber optic sensing ring under the temperature field;

[0021] Step 7.107: Calculate the asymmetric refractive index of the entanglement under thermal strain using the distributed temperature and strain characteristic parameter data of the fiber optic sensing loop obtained through multi-parameter decoupling. First, calculate the change in refractive index under thermal strain. The calculation formula is:

[0022]

[0023] in, For standard refractive index, and The photoelastic coefficient, For axial thermal strain. The thermo-optic coefficient of the optical fiber is given. Clockwise (CW) incident light within the fiber's sensing loop experiences a refractive index change at point 's' due to external temperature disturbance, resulting in a positive phase difference. Similarly, counterclockwise (CCW) incident light also exhibits a refractive index change at point 'Ls', but with a negative phase difference. Therefore, different refractive index changes occur along the symmetrical length. The refractive index changes at points 's' and 'Ls' for light incident from two different directions are then compared. By subtracting the values, an asymmetric distribution of the refractive index was obtained. The asymmetric refractive index distribution The calculation formula is:

[0024]

[0025] Step 8.108: Perform polarization crosstalk test on the sensitive ring of the fiber optic cable under test in this temperature field;

[0026] The radial stress of the fiber sensing ring under this temperature field was calculated using polarization crosstalk test data, and the asymmetric refractive index distribution was corrected. result;

[0027] Step 10: Divide the data according to the length of each layer of the measured fiber optic sensitive ring;

[0028] Step 111: Perform symmetry analysis of each layer / turn of the data in the divided fiber sensing loop under the temperature field;

[0029] Step 12: First, perform a turn symmetry analysis on the sensitive loop. One layer of fiber data along the symmetry length needs to be taken as a test unit.

[0030] Step 13: Next, perform layer symmetry analysis on the sensitive ring. The number of layers of a wrapped pole on the symmetry length should be taken as a test unit.

[0031] Step 14: Align the data of each test unit by layer / turn length;

[0032] Step 15: Perform correlation analysis on the aligned cell data to obtain the correlation coefficient distribution of the test cell along the symmetry length;

[0033] Step 16: Accumulate the correlation coefficient of the test unit along the length of the fiber sensing loop, and then integrate and sum to obtain the cumulative distribution of the correlation coefficient of the test unit along the length.

[0034] Step 17: Determine whether the correlation coefficient calculation of all test units on the fiber optic sensitive ring has been completed at this temperature point. If not, proceed to Step 18: If the correlation coefficient calculation of all test units on the fiber optic ring has been completed, proceed to Step 19:

[0035] Step 18: If the cross-correlation analysis of all test units on the tested fiber ring has not been completed, after completing the cumulative distribution calculation of the correlation coefficient along the length of the previous test unit, proceed to the next test unit and continue to perform the relevant operations from Step 11 to Step 16.

[0036] Step 19: After completing the correlation analysis calculation for all test units, accumulate the correlation coefficients of all test units on the fiber optic sensitive ring;

[0037] Step 20: Obtain the equivalent coherence coefficient of the fiber optic sensing loop at that temperature point;

[0038] Step 21: Determine if the current calculation is the last temperature point under the set temperature field full-temperature test conditions. If it is not the last temperature point under the full-temperature test conditions, execute the relevant operation in Step 22: If the current calculation is the last temperature point under the full-temperature test conditions, execute the relevant operation in Step 23:

[0039] Step 22: If this test is not the last temperature point in the full-temperature test conditions, then switch to the next temperature point in the temperature field and repeat the relevant operations from Step 4 to Step 20.

[0040] Step 23: If all the temperature points set under the full-temperature test conditions have been tested, the full-temperature equivalent correlation coefficient distribution results can be obtained.

[0041] Step 24: Perform outlier analysis on the full-temperature equivalent correlation coefficient of the fiber optic sensitive loop under temperature field excitation;

[0042] Step 25: Calculate the standard deviation of the full-temperature equivalent correlation coefficient of the fiber optic sensing loop;

[0043] The final result is the analysis of the physical symmetry of the overall fiber optic sensing ring under the temperature field.

[0044] The method for configuring the temperature field test conditions for the sensitive ring test in step 101 as described in claim 1 is attached. Figure 2 As shown, the temperature field configuration method specifically includes the following steps:

[0045] Step 1 201: First, you need to prepare a temperature field control device for experimental testing, a high-precision temperature chamber with customizable temperature change curves;

[0046] Step 202: Set the full temperature test range to -40℃ to 70℃, which is the extreme environmental conditions that the fiber optic sensing ring may reach during use.

[0047] Step 3 203: Set the interval between adjacent test temperature points in the temperature field to 5℃;

[0048] Step 4 204: Suspend the fiber optic sensing ring to be tested inside the temperature chamber to ensure that its four sides are heated evenly and that it does not come into contact with the inner wall of the temperature chamber, so as to avoid the influence of vibration and direct contact heat conduction on test errors.

[0049] Step 5.205: First, lower the temperature of the temperature field inside the chamber to the lowest temperature set in the full-temperature test temperature curve, i.e., -40℃.

[0050] Step 6.206: Keep the temperature at this point for one hour to ensure uniform temperature distribution inside the fiber optic sensing ring, and then use a high-performance OFDR system to perform distributed characteristic parameter measurement.

[0051] Step 7.207: After the lowest temperature point test is completed, the temperature is increased in increments of 5℃.

[0052] Step 8 208: After each temperature point reaches the set temperature, maintain the set temperature for one hour and then use the OFDR system to perform high-precision distributed characteristic parameter measurement.

[0053] Step 9 209: After the full-temperature test reaches the set maximum temperature of 70°C, keep it at that temperature for one hour and measure the distributed characteristic parameters of the sensitive ring under that temperature field.

[0054] Step 10: The high-precision OFDR testing system measures the distributed characteristic parameters of the sensitive loop of the fiber under test at 5°C intervals during the full-temperature test.

[0055] The full-temperature test of the fiber optic sensing ring under the temperature field has been completed.

[0056] The calculation process for the asymmetric refractive index distribution of the fiber optic sensitive loop described in step seven (107) of claim 1 is attached. Figure 4 As shown, the specific steps include:

[0057] Step 1 801: First, connect the pigtail of the fiber optic sensitive loop to the high-performance OFDR test system in the clockwise direction. After the test starts, the probe light enters the fiber optic sensitive loop in the clockwise direction.

[0058] Step 2 802: Perform multi-parameter decoupling processing on the test data detected by the OFDR system in the clockwise direction along the fiber optic sensitive loop;

[0059] Step 3 803: Demodulate to obtain the temperature change within the sensitive loop under this temperature field compared to the reference temperature. ;

[0060] Step 4.804: Simultaneously demodulate to obtain the axial thermal strain parameters of the sensitive ring under this temperature field. ;

[0061] Step 5.805: Calculate the refractive index change parameter of the sensitive ring during clockwise testing under this temperature field. ;

[0062] Step 6 806: Connect the pigtail of the fiber optic sensitive loop to the high-performance OFDR test system in the counterclockwise direction. After the test starts, the probe light enters the fiber optic sensitive loop in the counterclockwise direction.

[0063] Step 7.807: Perform multi-parameter decoupling processing on the test data detected by the OFDR system in the counterclockwise direction along the fiber optic sensitive loop.

[0064] Step 8.808: Demodulate to obtain the temperature change within the sensitive loop under this temperature field compared to the reference temperature. ;

[0065] Step 9.809: Simultaneously demodulate to obtain the axial thermal strain parameters of the sensitive ring under this temperature field. ;

[0066] Step 10: Calculate the refractive index change parameter of the sensitive ring during counterclockwise testing under this temperature field. ;

[0067] Step 11: Subtract the refractive index change parameters obtained from two different test directions to obtain the final asymmetric refractive index distribution. data;

[0068] Compared with the prior art, the advantages of the present invention are as follows:

[0069] This invention provides a quantitative method for measuring the physical symmetry of fiber optic sensitive loops and proposes an equivalent correlation coefficient to directly evaluate the physical symmetry of fiber optic loops.

[0070] The method provided by this invention, combined with high spatial resolution data, can provide an in-depth evaluation of the physical symmetry between layers and turns of an optical fiber ring, enabling the diagnosis of physical symmetry faults in the optical fiber ring.

[0071] The method provided by this invention plays an important role in optimizing the winding process of optical fiber rings, evaluating quality, and improving yield. Attached Figure Description

[0072] Figure 1 This is a flowchart of a method for measuring the physical symmetry of a fiber optic sensing ring under a temperature field.

[0073] Figure 2 This is a flowchart of the temperature field configuration during the full-temperature test;

[0074] Figure 3 This is a structural diagram of a high-performance OFDR test system described in a method for measuring physical symmetry under the temperature field of an optical fiber sensing ring.

[0075] Figure 4 This is a flowchart for calculating the asymmetric refractive index distribution of the fiber optic sensitive ring.

[0076] Figure 5 This is a diagram showing the asymmetric refractive index distribution of the fiber optic sensing ring under a temperature field.

[0077] Figure 6 This is a distribution diagram of the correlation coefficient between the inter-turn units of the fiber optic sensitive ring under a temperature field;

[0078] Figure 7 This is a graph showing the summation of the correlation coefficient of a unit on the sensitive loop along its length;

[0079] Figure 8 This is a diagram showing the final physical symmetry result of a single unit on the fiber optic sensing ring under a temperature field. Detailed Implementation

[0080] To clearly illustrate the method for measuring the physical symmetry of a fiber optic sensing ring under a temperature field according to the present invention, in conjunction with the appendix... Figure 3 The present invention will be further described, but this should not be construed as limiting the scope of protection of the present invention.

[0081] The apparatus for testing the physical symmetry of the fiber optic gyroscope sensing ring under a temperature field is attached. Figure 3 As shown, the selection of each device structure and the selection of component parameters are as follows:

[0082] The high-performance optical frequency domain reflection system (OFDR) consists of four main components: light source module 3, auxiliary interferometer module 4, main interferometer module 5, data acquisition and processing module 6, and temperature field testing module 7.

[0083] The light source 301 is a narrow linewidth tunable laser source. The wavelength scanning range is set to 10nm, the center wavelength is selected to be 1550nm, the scanning speed is 10nm / s, and the scanning time is 1s.

[0084] The maximum detection bandwidth of the first balanced photodetector 406, the second balanced photodetector 507, and the third balanced photodetector 508 is 200MHz.

[0085] The sampling frequency of the acquisition card 601 is set to 125MHz / s;

[0086] The reference arm delay fiber 403 in the auxiliary interferometer 4 is set to 250m. The auxiliary interferometer 4 adopts a Michelson interferometer structure with an arm length difference of 500m. The fiber used is a standard single-mode fiber with a refractive index n=1.456.

[0087] The splitting ratio of the first coupler 302 and the second coupler 501 is 1:99, and the splitting ratio of the third coupler 402 and the fourth coupler 504 is 50:50.

[0088] The fiber optic sensing loop 702 under test is connected to port 2 of the second circulator 503. A first Bragg grating 701 is connected at the entrance of the fiber optic sensing loop; at the same time, a second Bragg grating 703 is connected at the exit of the fiber optic sensing loop to mark the position of the pigtail of the fiber optic sensing loop under test.

[0089] A specific implementation of the present invention for testing the physical symmetry of an optical fiber sensing loop under a temperature field is as follows: A distributed optical frequency domain optical fiber sensing loop characteristic parameter testing sensing system, such as... Figure 3 As shown, the continuous sweeping light emitted by the light source 301 is split into two beams by the first coupler 302. 99% of the light enters the main interferometer 5. In the main interferometer 5, the second coupler 501 injects 99% of the light into the arm where the second circulator 503 is located to ensure that the Rayleigh backscattered light has sufficient intensity. The fiber optic sensitive loop 702 under test is connected to the second port of the second circulator 503. 1% of the light in the first coupler 302 enters the auxiliary interferometer module 4 of the optical frequency domain reflection system to generate an auxiliary beat frequency signal that characterizes the phase noise of the light source and provides compensation. The beat frequency interference light signals output by the main interferometer 5 and the auxiliary interferometer 4 are converted into electrical signals by the second balanced photodetector 507, the third balanced photodetector 508, and the first balanced photodetector 406, respectively. Then, the data is acquired by the acquisition card 601 and finally sent to the computer 602 for subsequent signal processing as described in this invention.

[0090] A method for measuring the physical symmetry of an optical fiber sensing ring under a temperature field, the specific usage process of which is as follows:

[0091] Step 1: First, the temperature field for testing the fiber optic sensitive loop needs to be configured to meet the temperature field testing conditions described in the method of this invention.

[0092] Step 2: Use a high-performance optical frequency domain reflection system to measure the distributed characteristic parameters of the fiber optic sensing loop located in the temperature field;

[0093] Step 3: Based on the testing requirements, select several representative specific temperature points within the temperature field for subsequent testing;

[0094] Step 4: Perform multi-parameter decoupling on the temperature and strain parameters in the distributed characteristic parameters obtained from the high-performance optical frequency domain reflection system test;

[0095] Step 5: Demodulate the distributed characteristic parameters to obtain the temperature change of the fiber optic sensing loop under the applied temperature field;

[0096] Step Six: Simultaneously, demodulating the parameters obtained from the high-performance OFDR test can yield the thermal strain of the fiber optic sensing ring under the temperature field;

[0097] Step 7: Calculate the asymmetric refractive index of the entanglement under thermal strain using the distributed temperature and strain characteristic parameter data of the fiber optic sensing loop obtained through multi-parameter decoupling. First, calculate the change in refractive index under thermal strain. The calculation formula is:

[0098]

[0099] in, For standard refractive index, and The photoelastic coefficient, For axial thermal strain. The thermo-optic coefficient of the optical fiber is given. Clockwise (CW) incident light within the fiber's sensing loop experiences a refractive index change at point 's' due to external temperature disturbance, resulting in a positive phase difference. Similarly, counterclockwise (CCW) incident light also exhibits a refractive index change at point 'Ls', but with a negative phase difference. Therefore, different refractive index changes occur along the symmetrical length. The refractive index changes at points 's' and 'Ls' for light incident from two different directions are then compared. By subtracting the values, an asymmetric distribution of the refractive index was obtained. The asymmetric refractive index distribution The calculation formula is:

[0100]

[0101] Step 8: Perform polarization crosstalk test on the sensitive ring of the fiber optic cable under test in this temperature field;

[0102] The radial stress of the fiber sensing ring under this temperature field was calculated using polarization crosstalk test data, and the asymmetric refractive index distribution was corrected. result;

[0103] Step 10: Divide the data according to the length of each layer of the measured fiber optic sensing ring;

[0104] Step 11: Perform symmetry analysis of each layer / turn of the data in the divided fiber sensing loop under the temperature field;

[0105] Step 12: First, perform a turn symmetry analysis on the sensitive loop, and take one layer of fiber data along the symmetry length as a test unit;

[0106] Step 13: Then perform layer symmetry analysis on the sensitive ring, and take the number of layers of a wrapped pole on the symmetry length as a test unit;

[0107] Step Fourteen: Align the data of each test unit according to the layer / turn length;

[0108] Step 15: Perform correlation analysis on the aligned cell data to obtain the distribution of correlation coefficients between inter-turn cells of the fiber optic sensitive ring under the temperature field, as shown below. Figure 6 As shown;

[0109] Step Sixteen: Accumulate the correlation coefficient of the test unit along the length of the fiber sensing loop, integrate and sum to obtain the cumulative distribution of the correlation coefficient of the test unit along the length, such as... Figure 7 As shown;

[0110] Step 17: Determine whether the correlation coefficient calculation of all test units on the fiber optic sensitive ring has been completed at this temperature point. If not, proceed to step 18. If the correlation coefficient calculation of all test units on the fiber optic ring has been completed, proceed to step 19.

[0111] Step 18: If the cross-correlation analysis of all test units on the tested fiber ring has not been completed, after completing the cumulative distribution calculation of the correlation coefficient along the length of the previous test unit, proceed to the next test unit and continue to perform the relevant operations from Step 111 to Step 16116.

[0112] Step 19: After completing the correlation analysis calculation for all test units, accumulate the correlation coefficients of all test units on the fiber optic sensitive ring;

[0113] Step 20: Obtain the equivalent coherence coefficient of the fiber optic sensing loop at that temperature point;

[0114] Step 21: Determine whether the current calculation is the last temperature point under the set temperature field full-temperature test conditions. If it is not the last temperature point under the full-temperature test conditions, execute the relevant operations in Step 22. If the current calculation is the last temperature point under the full-temperature test conditions, execute the relevant operations in Step 23.

[0115] Step 22: If this test is not the last temperature point in the full-temperature test conditions, then switch to the next temperature point in the temperature field and repeat the relevant operations from Step 4.104 to Step 20.120.

[0116] Step 23: If all the temperature points set under the full-temperature test conditions have been tested, the full-temperature equivalent correlation coefficient distribution results can be obtained;

[0117] Step 24: Perform outlier analysis on the full-temperature equivalent correlation coefficient of the fiber optic sensitive loop under temperature field excitation;

[0118] Step 25: Calculate the standard deviation of the full-temperature equivalent correlation coefficient of the fiber optic sensing loop;

[0119] Finally, the physical symmetry analysis results of the entire fiber optic sensing loop under the temperature field were obtained, such as... Figure 8 As shown.

Claims

1. A method for measuring the physical symmetry of an optical fiber sensing ring under a temperature field, wherein the method first requires the construction of a high-performance OFDR testing system to test the distributed characteristic parameters of the optical fiber sensing ring, specifically including temperature and strain data, and to calculate the refractive index variable based on this data, followed by layer-turn symmetry analysis; the method for measuring the symmetry of the optical fiber sensing ring under a temperature field is characterized by, The method includes the following steps: Step 1 (101): First, the temperature field for testing the fiber optic sensitive ring needs to be configured to meet the full-temperature test conditions described in this method. Step 2 (102): Use a high-performance optical frequency domain reflection system to perform distributed characteristic parameter measurements on the fiber optic sensing loop located in the temperature field; Step 3 (103): Based on the testing requirements, select several representative specific temperature points within the temperature field for subsequent testing; Step 4 (104): Perform multi-parameter decoupling on the temperature and strain parameters in the distributed characteristic parameters obtained from the high-performance optical frequency domain reflection system test; Step 5 (105): Demodulate the distributed characteristic parameters to obtain the temperature change of the fiber sensing loop in the applied temperature field; Step 6 (106): Simultaneously, demodulating the parameters obtained from the high-performance OFDR test can yield the thermal strain of the fiber sensing ring under the temperature field; Step 7 (107): Calculate the asymmetric refractive index α of the entanglement under thermal strain using the distributed temperature and strain characteristic parameter data of the fiber sensing loop obtained through multi-parameter decoupling. Ts First, calculate the change in refractive index α under thermal strain. T The calculation formula is: Where n0 is the standard refractive index, p 11 and p 12 ε is the photoelastic coefficient. θ For axial thermal strain, n T Let α be the thermo-optic coefficient of the optical fiber. Clockwise (CW) incident light within the fiber's sensing loop experiences a refractive index change at point s due to external temperature disturbance, resulting in a positive phase difference. Similarly, counterclockwise (CCW) incident light also exhibits a refractive index change at point Ls, but with a negative phase difference. Therefore, different refractive index changes occur along the symmetrical length. This can be expressed by measuring the refractive index change α at points s and Ls for the two incident directions. T By subtracting the values, we obtain the asymmetric distribution α of the refractive index. Ts The asymmetric refractive index distribution α Ts The calculation formula is: a Ts (s)=a T (s,T)-a T (Ls,T) Step 8 (108): Perform polarization crosstalk test on the sensitive ring of the fiber under test under this temperature field; Step 9 (109): The radial stress of the fiber sensing ring under this temperature field is calculated by converting the polarization crosstalk test data, and the asymmetric refractive index distribution α is corrected. Ts result; Step 10 (110): Divide the data according to the length of each layer of the measured fiber optic sensitive ring; Step 11 (111): Perform symmetry analysis of each layer / turn of the data in the divided fiber sensing loop under the temperature field; Step 12 (112): First, perform a turn symmetry analysis on the fiber ring. Take one layer of fiber data along the symmetry length as a test unit. Step 13 (113): Then perform layer symmetry analysis on the fiber ring, and take the number of layers of a wrapped pole on the symmetry length as a test unit; Step Fourteen (114): Align the data of each test unit by layer / turn length; Step 15 (115): Perform correlation analysis on the aligned cell data to obtain the correlation coefficient distribution of the test cell along the symmetry length; Step 16 (116): Accumulate the correlation coefficient of the test unit along the length of the fiber sensing loop, and then integrate and sum to obtain the cumulative distribution of the correlation coefficient of the test unit along the length; Step 17 (117): Determine whether the correlation coefficient calculation of all test units on the fiber optic sensitive ring has been completed at this temperature point. If not, proceed to step 18 (118). If the correlation coefficient calculation of all test units on the fiber optic ring has been completed, proceed to step 19 (119). Step 18 (118): If the correlation analysis of all test units on the tested fiber ring has not been completed, after the cumulative distribution calculation of the correlation coefficient along the length of the previous test unit is completed, proceed to the next test unit to continue the related operations from Step 11 (111) to Step 16 (116). Step 19 (119): After completing the correlation analysis calculation of all test units, accumulate the correlation coefficients of all test units on the fiber optic sensitive ring; Step 20 (120): Obtain the equivalent correlation coefficient of the measured fiber optic sensing loop at this temperature point; Step 21 (121): Determine whether the current calculation is the last temperature point under the full temperature test conditions of the set temperature field. If it is not the last temperature point under the full temperature test conditions, execute the relevant operation of step 22 (122). If the current calculation is the last temperature point under the full temperature test conditions, execute the relevant operation of step 23 (123). Step 22 (122): If this test is not the last temperature point in the full-temperature test conditions, then switch to the next temperature point of the temperature field and repeat the relevant operations from step 4 (104) to step 20 (120). Step 23 (123): If all the temperature points set under the full-temperature test conditions have been tested, the full-temperature equivalent correlation coefficient distribution results can be obtained; Step 24 (124): Perform outlier analysis on the full-temperature equivalent correlation coefficient of the fiber sensing loop under temperature field excitation; Step 25 (125): Calculate the standard deviation of the full-temperature equivalent correlation coefficient of the fiber sensing loop; The final result is the analysis of the physical symmetry of the overall fiber optic sensing ring under the temperature field.

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