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

Abstract

This invention provides a method for measuring the geometric symmetry of an optical fiber sensing ring, belonging to the fields of optical measurement and optical fiber sensing technology. The method includes: measuring the temperature change and thermal strain of the optical fiber ring at different temperatures; calculating the refractive index change under temperature changes; accumulating the asymmetric refractive index distribution of a layer / turn unit to obtain the geometric symmetry of the asymmetric refractive index representation unit; and accumulating the asymmetric refractive index of all units to obtain the equivalent asymmetric refractive index, thereby achieving the evaluation of geometric symmetry. This invention can achieve quantitative evaluation of geometric symmetry. Combined with high spatial resolution data, it can provide in-depth evaluation of the geometric symmetry between fiber layers and turns, diagnose geometric symmetry faults in the optical fiber ring, 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 geometric 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, fiber optic gyroscopes are susceptible to environmental changes; for example, fluctuations in ambient temperature can directly cause zero-point drift, severely limiting performance improvements.

[0003] Geometric symmetry refers to the symmetrical relationship in the geometric shape and size of the optical path layout in a gyroscope, also known as structural symmetry or length symmetry. It is reflected in the structural design and winding method of the fiber optic ring; that is, the gyroscope's optical path should exhibit mirror or rotational symmetry at the midpoint of its physical length, ensuring the consistency between the geometric center and the midpoint of the length. Good geometric symmetry ensures that fibers of the same length on both sides of the midpoint of the fiber optic ring are as close as possible, allowing these fibers to experience similar temperature disturbances and effectively reducing errors caused by temperature changes.

[0004] Optical frequency domain reflectometry (OFDR) was first proposed by Eickhoff in 1981. Since then, it has been widely studied and improved due to the advantages of its spatial resolution and dynamic range. However, the quality inspection of longer fiber optic gyroscope sensitive rings is limited by the trade-off between test length and sensing accuracy. For example, a fiber optic gyroscope optical path non-destructive testing device (CN103743412B) proposed by Ge Wenqian and Wang Wei of Beijing Aerospace Times Optoelectronics Technology Co., Ltd. uses an infrared camera to detect infrared light leaked from fiber defects after the gyroscope is powered on. It uses an infrared imaging system and the optical signal transmitted in the fiber optic cable to detect fiber defects, thus achieving defect detection of the wound and reinforced fiber. However, it can only detect damage defects in the fiber optic sensitive ring and cannot achieve quantitative detection and analysis of internal parameters such as the internal geometric symmetry of the 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). By applying radial and axial temperature excitation to the fiber optic ring and combining the simulation results of the three-dimensional mathematical model of the fiber optic ring, quantitative information on the radial and axial equivalent asymmetry of the fiber optic ring winding was obtained. However, due to limitations in the testing instruments and methods, it is currently not possible to achieve high-precision quantitative measurement of the full-temperature geometric symmetry of the sensing ring of a fiber optic gyroscope under a temperature field.

[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 a 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 measurements based on a high-precision OFDR testing system. Furthermore, this method cannot quantitatively evaluate and analyze the geometric symmetry affecting the gyroscope's optical path.

[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 characterizing the reciprocity symmetry of the fiber optic ring. 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 of the Brillouin back reflection detection technology, which prevents high-precision detection of fiber optic ring strain, and its 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 the fiber optic gyroscope in dynamic and static conditions at temperatures ranging from -55℃ to 80℃. However, this testing method can only perform overall qualification screening of the gyroscope system and cannot perform internal parameter tests such as symmetry tests on 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 to test the scaling stability of the gyroscope system. However, it is not suitable for quantitatively measuring the geometric symmetry of the gyroscope optical path under temperature fields.

[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 and geometric symmetries of the gyroscope's optical path under temperature fields, nor did it distinguish the impact of the two symmetries on the gyroscope's 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 provide a systematic quantitative evaluation of the geometric symmetry of the fiber optic sensitive loop.

[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 gyroscope's optical path 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 geometric symmetry of the gyroscope's optical path under temperature fields, and also provides direct and effective guidance for improving and adjusting the gyroscope's optical path. Summary of the Invention

[0014] A method for measuring the geometric 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 then calculate the refractive index variable of the winding. Subsequently, layer-turn symmetry analysis is performed. The method 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 full-temperature test conditions described in this method.

[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 full-temperature test 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 measured fiber optic sensing loop under the temperature field;

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

[0021] Step 7.107: Obtain distributed temperature and strain characteristic parameter data of the fiber optic sensing loop through multi-parameter decoupling, and the refractive index change 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;

[0024] Step 8.108: Perform polarization crosstalk test on the sensitive ring of the fiber optic cable under test in this temperature field;

[0025] Step 9.109: Calculate the radial stress of the fiber optic sensing ring under this temperature field using polarization crosstalk test data, and calculate the refractive index change. Make corrections;

[0026] Step 10: Divide the data according to the length of each layer of the measured fiber optic sensitive ring;

[0027] Step 111: Perform symmetry analysis of each layer / turn of the data in the divided fiber sensing loop under the temperature field;

[0028] 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.

[0029] 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.

[0030] Step 14.114: The probe light signal output from the high-performance OFDR test system is input into the fiber optic sensing loop in a clockwise direction. The clockwise (CW) incident light in the fiber optic sensing loop is subjected to external temperature disturbance at point s inside the fiber optic sensing loop, resulting in a change in refractive index. This results in a positive phase difference;

[0031] Step 15: Input the probe light signal output from the high-performance OFDR test system into the fiber optic sensing loop in a counterclockwise direction. The counterclockwise (CCW) incident light in the fiber optic sensing loop will also exhibit a refractive index change at Ls. However, this results in a negative phase difference;

[0032] Step 16: Therefore, different refractive index changes occur along the symmetry length. By comparing the refractive index changes produced by CW light and CCW light, subtract the refractive index change parameters at points s and Ls. An asymmetric distribution of the refractive index was obtained. .

[0033] Step 17.117: Asymmetric refractive index distribution The calculation formula is:

[0034]

[0035] Step 18: Accumulate the asymmetric refractive index distribution data of the test unit along its length;

[0036] Step 19: The cumulative distribution of the asymmetric refractive index of the test unit along the fiber length can then be obtained;

[0037] Step 20: Integrate the cumulative distribution of asymmetric refractive index along the fiber length;

[0038] Step 21: Obtain the asymmetric refractive index of the test unit after integration. asymmetric refractive index The calculation formula is:

[0039]

[0040] In the formula, 16 indicates that a sixteen-pole fiber sensing ring is selected as the test device, L is the total length of the fiber sensing ring, and m is half of the number of layers of the fiber sensing ring being measured, where m=32.

[0041] Step 22: Determine whether the asymmetric refractive index of all test units of the fiber optic loop at this temperature point has been completed for this test. If the asymmetric refractive index calculation for any remaining units is incomplete, proceed to step 23 (123). If the asymmetric refractive index calculation for all test units at that temperature point has been completed... If the calculation is not complete, then perform the relevant operations in step twenty-four 124;

[0042] Step 23: When the previous test unit has an asymmetric refractive index When the calculation is completed but it is not the last test unit of the fiber optic sensitive loop, switch to the next test unit and repeat the relevant operations from step 11.111 to step 22.122 until the asymmetric refractive index of all test units of the fiber optic sensitive loop is completed. Calculation;

[0043] Step 24: After the cycle is completed, the asymmetric refractive index calculation of all test units on the test fiber sensitive ring is completed, and the asymmetric refractive index of all units of the tested fiber sensitive ring under temperature field excitation is obtained.

[0044] Step 25: Accumulate the asymmetric refractive index of all test units on the fiber optic sensing ring;

[0045] Step 26: Obtain the equivalent asymmetric refractive index , This indicates the overall geometric symmetry of the measured fiber optic sensing loop, directly reflecting the winding quality of the fiber optic sensing loop. The calculation formula is as follows:

[0046]

[0047] Step 27: Determine whether the temperature field test is the last specific temperature point set in this full-temperature test. If not, execute the relevant operations in Step 28: If the temperature point of this test is the last specific temperature point set in the full-temperature test, execute the relevant operations in Step 29:

[0048] Step 28: Change the temperature point of the temperature field, and repeat all steps from Step 5 to Step 27 and their related operations.

[0049] Step 29: Iterate through all temperature points set in the temperature field and obtain the equivalent asymmetric refractive index at each temperature point. Then, the full-temperature equivalent asymmetric refractive index of the sensing ring of the fiber optic cable under test can be obtained. ;

[0050] Step 30: Perform outlier analysis on the full-temperature equivalent asymmetric refractive index of the fiber optic sensing loop under temperature field excitation;

[0051] Step 31: Calculate the standard deviation of the full-temperature equivalent asymmetric refractive index under temperature field excitation;

[0052] The final evaluation result of the geometric symmetry of the overall fiber optic sensing ring was obtained.

[0053] The temperature change curve of the sensitive ring test temperature field in step 101 as described in claim 1 is set as follows: Figure 2 As shown, the method for configuring the temperature curve specifically includes the following steps:

[0054] 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;

[0055] 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.

[0056] Step 3 203: Set the interval between adjacent test temperature points in the temperature field to 5℃;

[0057] 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.

[0058] 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℃.

[0059] 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.

[0060] Step 7.207: After the lowest temperature point test is completed, the temperature is increased in increments of 5℃.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] The full-temperature test of the fiber optic sensing ring under the temperature field has been completed.

[0065] Compared with the prior art, the advantages of the present invention are as follows:

[0066] This invention provides a quantitative method for measuring the geometric symmetry of fiber optic sensitive rings and proposes an equivalent asymmetric refractive index to directly evaluate the geometric symmetry of fiber optic rings.

[0067] 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 geometric symmetry faults in the optical fiber ring.

[0068] 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

[0069] Figure 1 This is a flowchart of a method for measuring the geometric symmetry of a fiber optic sensing ring under a temperature field.

[0070] Figure 2 This is a flowchart of the temperature field configuration in a full-temperature test process of a geometric symmetry measurement method under the temperature field of an optical fiber sensing ring.

[0071] Figure 3 This is a structural diagram of a high-performance OFDR test system described in a method for measuring the geometric symmetry of an optical fiber sensing ring under a temperature field.

[0072] Figure 4 This refers to the data on the change in refractive index of the fiber optic sensitive ring under the temperature field during the testing process described in this invention.

[0073] Figure 5 It is the result of the asymmetric distribution of the refractive index of the fiber sensing ring under temperature field excitation;

[0074] Figure 6 This is the result of the accumulation of the asymmetric refractive index of the inter-turn unit along the length;

[0075] Figure 7 This is a graph showing the cumulative asymmetric refractive index of multiple units on the fiber optic sensing ring;

[0076] Figure 8 This is a diagram showing the calculated results of the overall geometric symmetry of the fiber optic sensing loop at a given temperature point. Detailed Implementation

[0077] To clearly illustrate the method for measuring the geometric 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.

[0078] The apparatus for testing the geometric symmetry of the sensing ring of a fiber optic gyroscope 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:

[0079] The high-performance optical frequency domain reflection system (OFDR) consists of four main components: a light source module 30, an auxiliary interferometer module 40, a main interferometer module 50, a data acquisition and processing module 60, and a temperature field testing module 70.

[0080] The light source 301 used in the test system is a narrow linewidth tunable laser source. Its wavelength scanning range is set to 10nm, the center wavelength is selected as 1550nm, the scanning speed is 10nm / s, and the scanning time is 1s.

[0081] The maximum detection bandwidth of the first balanced photodetector 406, the second balanced photodetector 507, and the third balanced photodetector 508 is 200MHz.

[0082] The sampling frequency of the acquisition card 601 is set to 125MHz / s;

[0083] The total length of the reference arm delay fiber 403 in the auxiliary interferometer module 40 is set to 250m. The auxiliary interferometer 40 of the test device used in this invention adopts the Michelson interferometer structure, so its arm length difference is 500m. The fiber used is a standard single-mode fiber with a refractive index n=1.456.

[0084] 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.

[0085] 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.

[0086] A specific implementation of the method for testing the geometric symmetry of an optical fiber sensing loop under a temperature field according to the present invention is as follows: A distributed optical fiber sensing loop characteristic parameter testing sensing system in the optical frequency domain is used... Figure 3As shown, the continuously swept 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 containing the second circulator 503 to ensure sufficient intensity of the Rayleigh backscattered light. The fiber optic sensitive loop 702 under test is connected to the second port of the second circulator 503. 1% of the light from the first coupler 302 enters the auxiliary interferometer module 4 of the optical frequency domain reflection system to generate an auxiliary beat frequency signal characterizing the phase noise and compensation of the light source. 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, data is acquired by the acquisition card 601 and finally sent to the computer 602 for further processing as described in this invention. This yields an evaluation index of the full-temperature geometric symmetry of the fiber optic sensitive loop under temperature field excitation.

[0087] A method for measuring the geometric symmetry of an optical fiber sensing ring under a temperature field, specifically including the following steps:

[0088] Step 101: First, the temperature field for testing the fiber optic sensitive loop needs to be configured to meet the full-temperature test conditions described in this method.

[0089] 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;

[0090] Step 3.103: Based on the full-temperature test requirements, select several representative specific temperature points within the temperature field for subsequent testing;

[0091] 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;

[0092] Step 5.105: Demodulate the distributed characteristic parameters to obtain the temperature change of the measured fiber optic sensing loop under the temperature field;

[0093] Step 6.106: Simultaneously demodulating the test data from the high-performance OFDR can yield the thermal strain of the fiber optic sensing loop under the temperature field;

[0094] Step 7.107: Obtain distributed temperature and strain characteristic parameter data of the fiber optic sensing loop through multi-parameter decoupling, and the refractive index change under thermal strain. The calculation formula is:

[0095]

[0096] in, For standard refractive index, and The photoelastic coefficient, For axial thermal strain. The thermo-optic coefficient of the optical fiber is given by the calculated result of the refractive index change of the fiber sensing ring under the temperature field, as shown below. Figure 4 As shown;

[0097] Step 8.108: Perform polarization crosstalk test on the sensitive ring of the fiber optic cable under test in this temperature field;

[0098] Step 9.109: Calculate the radial stress of the fiber optic sensing ring under this temperature field using polarization crosstalk test data, and calculate the refractive index change. Make corrections;

[0099] Step 10: Divide the data according to the length of each layer of the measured fiber optic sensitive ring;

[0100] Step 111: Perform symmetry analysis of each layer / turn of the data in the divided fiber sensing loop under the temperature field;

[0101] 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.

[0102] 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.

[0103] Step 14.114: The probe light signal output from the high-performance OFDR test system is input into the fiber optic sensing loop in a clockwise direction. The clockwise (CW) incident light in the fiber optic sensing loop is subjected to external temperature disturbance at point s inside the fiber optic sensing loop, resulting in a change in refractive index. This results in a positive phase difference;

[0104] Step 15: Input the probe light signal output from the high-performance OFDR test system into the fiber optic sensing loop in a counterclockwise direction. The counterclockwise (CCW) incident light in the fiber optic sensing loop will also exhibit a refractive index change at Ls. However, this results in a negative phase difference;

[0105] Step 16: Therefore, different refractive index changes occur along the symmetry length. By comparing the refractive index changes produced by CW light and CCW light, subtract the refractive index change parameters at points s and Ls. An asymmetric distribution of the refractive index was obtained. The calculation results are attached. Figure 5 As shown.

[0106] Step 17.117: Asymmetric refractive index distribution The calculation formula is:

[0107]

[0108] Step 18: Accumulate the asymmetric refractive index distribution data of the test unit along its length;

[0109] Step 19: The cumulative distribution of the asymmetric refractive index of the test unit along the fiber length can then be obtained, as shown in the attached figure. Figure 6 As shown;

[0110] Step 20: Integrate the cumulative distribution of asymmetric refractive index along the fiber length;

[0111] Step 21: Obtain the asymmetric refractive index of the test unit after integration. asymmetric refractive index The calculation formula is:

[0112]

[0113] In the formula, 16 indicates that a sixteen-pole fiber optic sensing loop is used as the test device, L is the total length of the fiber optic sensing loop, and m is half the number of layers of the fiber optic sensing loop being measured; here, m = 32. The final calculated result of the full-element asymmetric refractive index is attached. Figure 7 As shown;

[0114] Step 22: Determine whether the asymmetric refractive index of all test units of the fiber optic loop at this temperature point has been completed for this test. If the asymmetric refractive index calculation for any remaining units is incomplete, proceed to step 23 (123). If the asymmetric refractive index calculation for all test units at that temperature point has been completed... If the calculation is not complete, then perform the relevant operations in step twenty-four 124;

[0115] Step 23: When the previous test unit has an asymmetric refractive index When the calculation is complete but it is not the last test unit of the fiber optic sensitive loop, switch to the next test unit and repeat the relevant operations of steps eleven to twenty-two until the asymmetric refractive index of all test units of the fiber optic sensitive loop is completed. Calculation;

[0116] Step 24: After the cycle is completed, the asymmetric refractive index calculation of all test units on the test fiber sensitive ring is completed, and the asymmetric refractive index of all units of the tested fiber sensitive ring under temperature field excitation is obtained.

[0117] Step 25: Accumulate the asymmetric refractive index of all test units on the fiber optic sensing ring;

[0118] Step 26: Obtain the equivalent asymmetric refractive index , This indicates the overall geometric symmetry of the measured fiber optic sensing loop, directly reflecting the winding quality of the fiber optic sensing loop. The calculation formula is as follows:

[0119]

[0120] Step 27: Determine whether the temperature field test is the last specific temperature point set in this full-temperature test. If not, execute the relevant operation in Step 28. If the temperature point of this test is the last specific temperature point set in the full-temperature test, execute the relevant operation in Step 29.

[0121] Step 28: Change the temperature point of the temperature field, and repeat all steps from Step 5 to Step 27 and their related operations.

[0122] Step 29: Iterate through all temperature points set in the temperature field and obtain the equivalent asymmetric refractive index at each temperature point. Then, the full-temperature equivalent asymmetric refractive index of the sensing ring of the fiber optic cable under test can be obtained. ;

[0123] Step 30: Perform outlier analysis on the full-temperature equivalent asymmetric refractive index of the fiber optic sensing loop under temperature field excitation;

[0124] Step 31: Calculate the standard deviation of the full-temperature equivalent asymmetric refractive index under temperature field excitation;

[0125] The final evaluation results of the overall fiber optic sensing loop's geometric symmetry are shown in the attached figure. Figure 8 As shown.

Claims

1. A method for measuring the geometric 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 of the winding body based on this data, followed by layer-turn symmetry analysis; the method for measuring the geometric symmetry of an optical fiber sensing ring under a temperature field is characterized in that, 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 measure the distributed characteristic parameters of the fiber optic sensing loop located in the temperature field; Step 3 (103): Based on the requirements of the full-temperature test, select several specific temperature points that are relatively representative 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 measured fiber sensing loop under the temperature field; Step 6 (106): Simultaneously demodulate the high-performance OFDR test data to obtain the thermal strain generated by the fiber optic sensing ring under the temperature field; Step 7 (107): Distributed temperature and strain characteristic parameter data of the fiber optic sensing loop obtained through multi-parameter decoupling, and the refractive index change 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 The thermo-optic coefficient of the optical fiber; 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 refractive index change α is calculated. T Make corrections; 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 sensitive loop. One layer of fiber data along the symmetry length needs to be taken as a test unit. Step 13 (113): 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. Step Fourteen (114): The probe light signal output by the high-performance OFDR test system is input into the fiber optic sensing loop in a clockwise direction. The clockwise (CW) incident light in the fiber optic sensing loop is subjected to external temperature disturbance at point s in the fiber optic sensing loop, resulting in a refractive index change α. T (s,T) results in a positive phase difference; Step 15 (115): Input the probe light signal output by the high-performance OFDR test system into the fiber optic sensing loop in a counterclockwise direction. The counterclockwise (CCW) incident light in the fiber optic sensing loop will also have a refractive index change α at Ls. T (Ls,T), but produces a negative phase difference; Step 16 (116): Therefore, different refractive index changes are produced along the symmetry length. By comparing the amount of refractive index change produced by the CW incident light and the CCW incident light, the refractive index change parameter α of point s and point Ls is subtracted. T The asymmetric distribution α of the refractive index was obtained. Ts ; Step 17 (117): where the asymmetric refractive index distribution α Ts The calculation formula is: a Ts (s)=a T (s,T)-a T (Ls,T) Step 18 (118): Accumulate the asymmetric refractive index distribution data of the test unit along its length; Step 19 (119): The cumulative distribution of the asymmetric refractive index of the test unit along the fiber length can be obtained; Step 20 (120): Integrate the cumulative distribution of asymmetric refractive index along the fiber length; Step 21 (121): After integration, the asymmetric refractive index α of the test unit is obtained. Tj asymmetric refractive index α Tj The calculation formula is: In the formula, 16 indicates that a sixteen-pole fiber sensing ring is selected as the test device, L is the total length of the fiber sensing ring, and m is half of the number of layers of the fiber sensing ring being measured, where m = 32. Step 22 (122): Determine whether the asymmetric refractive index α of all test units of the fiber optic loop at this temperature point has been completed for this test. Tj If the asymmetric refractive index calculation for any unit is still incomplete, proceed to step twenty-three (123). If the asymmetric refractive index α of all test units at this temperature point has been calculated, proceed to step twenty-three (123). Tj If the calculation is performed, then the relevant operation in step twenty-four (124) will be executed; Step 23 (123): When the asymmetric refractive index α of the previous test unit Tj When the calculation is completed and it is not the last test unit of the fiber optic sensitive loop, switch to the next test unit and repeat the relevant operations from step eleven (111) to step twenty-two (122) until the asymmetric refractive index α of all test units of the fiber optic sensitive loop is completed. Tj Calculation; Step 24 (124): After the cycle is completed, the asymmetric refractive index calculation of all test units on the test fiber sensitive ring is completed, and the asymmetric refractive index of all units of the tested fiber sensitive ring under temperature field excitation is obtained. Step 25 (125): Accumulate the asymmetric refractive index of all test units on the fiber optic sensitive loop; Step 26 (126): Obtain the equivalent asymmetric refractive index α Tk α Tk This indicates the overall geometric symmetry of the measured fiber optic sensing loop, directly reflecting the winding quality of the fiber optic sensing loop. The calculation formula is as follows: Step 27 (127): Determine whether the temperature field test is the last specific temperature point set in this full-temperature test. If not, execute the relevant operation of step 28 (128). If the temperature point of this test is the last specific temperature point set in the full-temperature test, execute the relevant operation of step 29 (129). Step 28 (128): Change the temperature point of the temperature field and repeat all steps from Step 5 (105) to Step 27 (127) and their related operations; Step 29 (129): Traverse all temperature points set in the temperature field and obtain the equivalent asymmetric refractive index α at each temperature point. Tk Then, the full-temperature equivalent asymmetric refractive index α of the sensing loop of the fiber under test can be obtained. Tk ; Step 30 (130): Perform outlier analysis on the full-temperature equivalent asymmetric refractive index of the fiber optic sensing loop under temperature field excitation; Step 31 (131): Calculate the standard deviation of the full-temperature equivalent asymmetric refractive index under temperature field excitation; The final evaluation result of the geometric symmetry of the overall fiber optic sensing ring was obtained.

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