Method for measuring geometric symmetry of optical fiber sensitive ring in temperature field

Abstract

The invention provides a geometric symmetry measurement method for an optical fiber sensitive ring, and belongs to the technical field of optical measurement and optical fiber sensing. The method comprises the following steps: measuring temperature variation and thermal strain of the optical fiber ring at different temperatures; calculating the refractive index variation under temperature variation, accumulating the asymmetric refractive index distribution of one layer / turn unit to obtain the geometric symmetry of the asymmetric refractive index representation unit, and accumulating the asymmetric refractive indexes of the whole unit to obtain the equivalent asymmetric refractive index so as to realize the evaluation of the geometric symmetry. According to the method, quantitative geometric symmetry evaluation can be realized, the interlayer and turn-to-turn geometric symmetry of the optical fiber can be deeply evaluated in combination with data with high spatial resolution, the geometric symmetry fault of the optical fiber ring is diagnosed, and the method plays an important role in winding process optimization, quality evaluation and yield improvement of the optical fiber ring.

Description

Technical Field

[0001] This patented method belongs to the field of fiber optic gyroscope testing, and specifically involves a method for testing the geometric symmetry of a fiber optic sensitive ring under a temperature field based on optical frequency domain reflection. Background Art

[0002] Fiber optic gyroscope is a high-precision angular velocity measuring instrument based on Sagnac effect invented in the 1970s. However, fiber optic gyroscope is easily affected by environmental changes. For example, the fluctuation of external ambient temperature will directly cause the zero drift of fiber optic gyroscope, which seriously limits the improvement of gyroscope performance.

[0003] Geometric symmetry refers to the symmetric relationship between the geometric shape and size of the optical path layout in the 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 optical path should show mirror or rotational symmetry at the midpoint of the physical length to ensure the consistency between the geometric center and the midpoint of the length. Good geometric symmetry makes the distance between optical fibers of the same length on both sides of the midpoint of the fiber optic ring as close as possible, so that the optical fibers at these positions experience similar temperature disturbances, effectively reducing the errors caused by temperature changes.

[0004] Optical frequency domain reflection technology was first proposed by Eickhoff in 1981. Since then, it has been widely studied and improved due to the advantages of the spatial resolution and dynamic range of the optical frequency domain reflection system. However, due to the mutual constraints between the test length and the sensing accuracy, it is impossible to achieve quality inspection of the sensitive ring of a longer fiber optic gyroscope. For example, Ge Wenqian, Wang Wei and others from Beijing Aerospace Times Optoelectronics Technology Co., Ltd. proposed a fiber optic gyroscope optical path nondestructive testing device (CN103743412B), which uses an infrared camera to detect infrared light leaked from the optical fiber defect after the gyroscope is powered on, and uses an infrared imaging system and the optical signal transmitted in the optical fiber of the fiber optic gyroscope to detect optical fiber defects, thereby realizing defect detection of the optical fiber after winding and reinforcement. However, it can only detect damage defects of the optical fiber sensitive ring, and cannot realize quantitative detection and analysis of internal parameters such as the internal geometric symmetry of the sensitive ring.

[0005] In 2008, Yao Xiaotian and others from Beijing Gaoguang Technology Co., Ltd. announced a method and device for measuring the quality of fiber optic rings for fiber optic gyroscopes (CN101339093B). By applying radial and axial temperature excitations to the fiber optic rings and combining the simulation results of the three-dimensional mathematical model of the fiber optic rings, quantitative information on the radial and axial equivalent asymmetry of the fiber optic ring windings was obtained. However, due to the limitations of their test instruments and test methods, it is currently impossible to achieve high-precision quantitative measurement of the full-temperature geometric symmetry of the fiber optic gyroscope sensitive ring under temperature fields.

[0006] In 2012, Suzhou Guanghuan Technology Co., Ltd. disclosed a method and device for detecting the quality of optical fiber rings for gyroscopes (CN103048115B). A radial temperature excitation is applied to the optical fiber ring to be tested, and the equivalent asymmetric length of the optical fiber ring to be tested is determined by measurement, thereby determining the quality of the optical fiber ring. Due to the limitations of its test instrument and test method, it is unable to achieve the accuracy measured by a high-precision OFDR test system, and this method is also unable to quantitatively evaluate and analyze the geometric symmetry that affects the gyroscope optical path.

[0007] In 2014, Yang Dongkun and others from the 618th Institute of China Aviation Industry proposed a method for evaluating and compensating the reciprocal symmetry of an optical fiber ring (CN104296964B). The invention uses enhanced Brillouin backreflection detection technology to obtain the internal stress state distribution data of the optical fiber ring that characterizes the reciprocal symmetry. The distribution data is used to establish a symmetry model within the working temperature range and analyze and evaluate the reciprocal symmetry of the optical fiber ring to be tested; according to the optimal reciprocal symmetry position and the error size and error direction, 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 backreflection detection technology and cannot perform high-precision detection of the strain of the optical fiber ring, and its stress state distribution data has a large error.

[0008] Beijing Zhongke Panhua Measurement & Control Technology Co., Ltd. proposed a fiber optic gyroscope test system and test method (CN117191078A). This method places several fiber optic gyroscope groups on a test turntable in an incubator. The incubator adjusts the temperature according to a preset temperature curve, and the test turntable adjusts the preset speed to drive the fiber optic gyroscope group to rotate; the output voltage value corresponding to the fiber optic gyroscope is obtained through a data acquisition board; the predicted output voltage value of the gyroscope system output voltage is compared with the actual output voltage value to obtain the judgment result of the fiber optic gyroscope group; it is used to test the performance parameters of the fiber optic gyroscope in the temperature range of -55°C to 80°C during dynamic and static periods. This test method can only perform qualification screening on the gyroscope system as a whole and cannot perform internal parameter tests such as symmetry on the fiber optic sensitive ring.

[0009] In 2019, the 707th Institute of China Shipbuilding Industry Corporation disclosed a fiber optic gyroscope ring assembly scale stability test and analysis method (CN109357690A). This method divides the fiber optic gyroscope into a ring assembly module (including a ring and Y-waveguide) and an optoelectronic module (including a light source and a circuit), and excludes the influencing factors of the fiber optic gyroscope other than the ring assembly to the greatest extent possible to test the stability of the gyroscope system scale factors. However, it is not suitable for quantitative measurement of the geometric symmetry of the gyroscope optical path under the temperature field.

[0010] In 2017, the Tianjin Navigation Instrument Research Institute published a paper (THE EXPRESS TEST OF WINDING SYMMETRYQUALITY IN FOG FIBER COILS) that experimentally studied the symmetry characteristics of the fiber optic gyroscope ring under periodic temperature excitation, and introduced the equivalent asymmetry (EAD) to quantify the winding symmetry quality of the fiber optic coil. A fast 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 and explain in detail the physical and geometric symmetry of the gyroscope optical path under the temperature field, nor did it distinguish the impact of the two symmetries on the gyroscope performance.

[0011] In 2021, Beijing Aerospace Times Optoelectronics Technology Co., Ltd. published a paper (Optical Fiber Ring Temperature Performance Evaluation Method Based on Equivalent Asymmetric Length). According to the Shupe error mechanism, it can be known that only when the equivalent midpoint coincides with the physical midpoint can the zero bias error caused by temperature on both sides of the equivalent midpoint be completely opposite. This paper proposes an optical fiber ring evaluation method based on equivalent asymmetric length, and quantitatively evaluates the symmetry of the optical fiber ring through the equivalent asymmetric length of the optical fiber ring.

[0012] In 2023, the 16th Institute of China Aerospace Science and Technology Corporation published a paper on precision winding technology, which found that the symmetry of the fiber ring affects the temperature performance of the fiber optic gyroscope. Fiber rings with good symmetry also have good temperature performance. The OFDR-based fiber ring optical center detection method used in this paper can effectively detect the optical asymmetry of the fiber ring relative to the center point, but it does not make a systematic quantitative evaluation of the geometric symmetry of the fiber sensitive ring.

[0013] The above evaluation and testing methods are helpful for the symmetry screening of optical fiber rings under temperature fields, but have no guiding significance for the application and improvement of optical fiber gyroscopes. The symmetry of the gyroscope optical path under temperature fields is a manifestation of the comprehensive performance of optical fiber gyroscopes. This parameter is affected by many factors such as the winding method of the optical fiber sensitive ring, the optical fiber winding state, and the strain distribution of the overall gyroscope optical path. It is not only a key factor in determining the temperature performance of optical fiber gyroscopes, but the method described in the present invention can accurately evaluate the geometric symmetry of the gyroscope optical path under temperature fields, and at the same time has a direct and effective guiding role in the improvement and adjustment of the gyroscope optical path. Summary of the invention

[0014] A method for measuring the geometric symmetry of an optical fiber sensitive ring under a temperature field, wherein the method first requires the construction of a high-performance OFDR test system, tests the distributed characteristic parameter (temperature and strain) data of the optical fiber sensitive ring, and calculates the refractive index variable of the winding body based on the data, and then performs a layer turn symmetry analysis; the method for measuring the geometric symmetry of an optical fiber sensitive ring under a temperature field is characterized in that the method comprises the following steps:

[0015] Step 1 101: First, the temperature field for the optical fiber sensitive ring test needs to be configured to meet the temperature field full-temperature test conditions described in the method;

[0016] Step 2 102: Use a high-performance optical frequency domain reflectometry system to measure distributed characteristic parameters of the optical fiber sensitive ring in the temperature field;

[0017] Step 3 103: According to the full temperature test requirements, several representative specific temperature points in the temperature field are selected for subsequent testing;

[0018] Step 4 104: performing multi-parameter simultaneous decoupling processing on the temperature and strain parameters in the distributed characteristic parameters obtained by the high-performance optical frequency domain reflectometry system test;

[0019] Step five 105: Demodulating the distributed characteristic parameters to obtain the temperature variation of the optical fiber sensitive ring under the temperature field;

[0020] Step 6 106: demodulating the high-performance OFDR test data to obtain the thermal strain generated by the optical fiber sensitive ring under the temperature field;

[0021] Step 7 107: Distributed temperature and strain characteristic parameter data of the optical fiber sensitive ring obtained by multi-parameter decoupling, and the refractive index change under thermal strain The calculation formula is:

[0022]

[0023] in, is the standard refractive index, and is the photoelastic coefficient, is the axial thermal strain, is the thermo-optical coefficient of the optical fiber;

[0024] Step eight 108: performing a polarization crosstalk test on the optical fiber sensitive ring to be tested under the temperature field;

[0025] Step 9 109: The radial stress of the optical fiber sensitive ring under the temperature field is obtained by converting the polarization crosstalk test data, and the refractive index change make corrections;

[0026] Step ten 110: dividing the data according to the length of each layer of the measured optical fiber sensitive ring;

[0027] Step 111: performing symmetry analysis of each layer / turn of the divided optical fiber sensitive ring under the temperature field;

[0028] Step 12 112: Firstly, the turn symmetry analysis of the sensitive loop is performed, and a layer of optical fiber data on a symmetrical length needs to be taken as a test unit;

[0029] Step 13 113: Secondly, the layer symmetry analysis of the sensitive ring is performed, and the number of layers of a winding pole on the symmetrical length needs to be taken as a test unit;

[0030] Step 14 114: Input the detection light signal output by the high-performance OFDR test system into the fiber sensitive ring in the clockwise direction. The clockwise (CW) incident light in the fiber sensitive ring is disturbed by the external temperature at point s in the fiber sensitive ring, resulting in a refractive index change. , resulting in a positive phase difference;

[0031] Step 15: Input the detection light signal output by the high-performance OFDR test system into the fiber sensitive ring in the counterclockwise direction. The counterclockwise (CCW) incident light in the fiber sensitive ring will also have a refractive index change at Ls. , but a negative phase difference is produced;

[0032] Step 16 116: Therefore, different refractive index changes are generated on the symmetrical length. By comparing the refractive index changes generated by the CW light and the CCW light, the refractive index change parameters of point s and point Ls are subtracted. , and the asymmetric distribution of the refractive index is obtained .

[0033] Step 17 117: Asymmetric refractive index distribution The calculation formula is:

[0034]

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

[0036] Step 19 119: the cumulative distribution result of the asymmetric refractive index of the test unit along the length of the optical fiber can be obtained;

[0037] Step 20 120: Integrate the cumulative distribution result of the asymmetric refractive index along the length of the optical fiber along the length;

[0038] Step 21 121: 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 hexadecanopole optical fiber sensitive ring is selected as the test device, L is the total length of the optical fiber sensitive ring, and m is half of the number of layers of the measured optical fiber sensitive ring, where m=32;

[0041] Step 22 122: Determine whether the asymmetric refractive index of all test units of the optical fiber ring under the temperature point has been completed. If there are still units that have not completed the calculation of the asymmetric refractive index, then execute the relevant operations of step 23 123. If the asymmetric refractive index of all test units at this temperature point has been completed, , then execute the related operations of step twenty-four 124;

[0042] Step 23 123: When the previous test unit has an asymmetric refractive index When the calculation is completed and it is not the last test unit of the test optical fiber sensitive ring, the next test unit is switched to repeat the relevant operations of step 111 to step 22 122 until the asymmetric refractive index of all test units of the optical fiber sensitive ring is completed. Calculation of

[0043] Step 24 124: when the cycle is finished, the calculation of the asymmetric refractive index of all the test units on the test optical fiber sensitive ring has been completed, and the asymmetric refractive index of all the units of the tested optical fiber sensitive ring under the excitation of the temperature field is obtained;

[0044] Step 25 125: Accumulating the asymmetric refractive index of all test units on the optical fiber sensitive ring;

[0045] Step 26 126: Obtaining the equivalent asymmetric refractive index , It indicates the overall geometric symmetry of the measured optical fiber sensitive ring, which directly reflects the winding quality of the optical fiber sensitive ring. The calculation formula is:

[0046]

[0047] 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 related operations of step 28 128, if the temperature point of this test is the last specific temperature point in the set full temperature test, execute the related operations of step 29 129;

[0048] Step 28 128: Change the temperature point of the temperature field, and repeat all steps from step 5 105 to step 27 127 and related operations;

[0049] Step 29: Traverse all temperature points set in the temperature field and obtain the equivalent asymmetric refractive index at each temperature point After that, the full-temperature equivalent asymmetric refractive index of the optical fiber sensitive ring to be tested can be obtained. ;

[0050] Step 30 130: performing an outlier analysis on the full-temperature equivalent asymmetric refractive index of the optical fiber sensitive ring to be tested under the excitation of the temperature field;

[0051] Step 31 131: Calculate the standard deviation of the full-temperature equivalent asymmetric refractive index under temperature field excitation;

[0052] Finally, the geometric symmetry evaluation result of the overall optical fiber sensitive ring is obtained.

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

[0054] Step 1 201: First, you need to prepare a temperature field control device for experimental testing, which can customize the high-precision temperature change curve;

[0055] Step 2 202: Setting the full temperature test range to -40°C to 70°C, i.e., the extreme environmental conditions that the optical fiber sensitive ring may reach during use;

[0056] Step 3 203: setting the interval between adjacent test temperature points of the temperature field to 5°C;

[0057] Step 4 204: Install the optical fiber sensitive ring to be tested in the temperature chamber in the air, ensure that the four sides are evenly heated and do not contact the inner wall of the temperature chamber, and avoid vibration and direct contact heat conduction to cause test errors;

[0058] Step 5 205: firstly, the temperature of the temperature field in the temperature box is lowered to the lowest temperature set by the full temperature test temperature curve, i.e. -40°C;

[0059] Step 6 206: Keep the temperature at this point for one hour to make the temperature inside the optical fiber sensitive ring evenly distributed, 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 by 5°C as a temperature point;

[0061] Step eight 208: After each temperature point reaches the set temperature, it is maintained at the set temperature for one hour, and then a high-precision distributed characteristic parameter measurement is performed using an OFDR system;

[0062] Step nine 209: After the full temperature test reaches the set maximum temperature of 70° C., keep the temperature for one hour, and measure the distributed characteristic parameters of the sensitive ring under the temperature field;

[0063] Step ten 210: the high-precision OFDR test system performs distributed characteristic parameter measurement of the optical fiber sensitive ring to be tested at 5° C. as a test temperature point during the full-temperature test;

[0064] The full temperature test of the optical fiber sensitive ring under the temperature field is completed.

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

[0066] The invention provides a quantitative method for measuring the geometric symmetry of an optical fiber sensitive ring, and proposes a method for directly evaluating the geometric symmetry of an optical fiber ring by using an equivalent asymmetric refractive index.

[0067] The method provided by the present invention, combined with data of high spatial resolution, can deeply evaluate the physical symmetry between layers and turns of an optical fiber ring, and realize the diagnosis of geometric symmetry faults of an optical fiber ring.

[0068] The method provided by the present invention plays an important role in optimizing the winding process, evaluating the quality, and improving the yield of optical fiber rings. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 It is a flow chart of a method for measuring geometric symmetry of a fiber optic sensitive ring under a temperature field;

[0070] Figure 2 It is a temperature field configuration flow chart of the full temperature test process in the method of measuring geometric symmetry under the temperature field of an optical fiber sensitive ring;

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

[0072] Figure 4 It is the data of the refractive index variation of the optical fiber sensitive ring under the temperature field during the test process of the method of the present invention;

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

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

[0075] Figure 7 It is a graph showing the cumulative results of asymmetric refractive index of multiple units on the optical fiber sensitive ring;

[0076] Figure 8 This is a diagram showing the calculation results of the overall geometric symmetry of the optical fiber sensitive ring at one temperature point. DETAILED DESCRIPTION

[0077] In order to clearly explain the method for measuring the geometric symmetry of a fiber optic sensitive ring under temperature field of the present invention, the following is a Figure 3 The present invention is further described, but the protection scope of the present invention should not be limited thereto.

[0078] The geometric symmetry test device of the fiber optic gyroscope sensitive ring under temperature field is as shown in the attached figure. 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 reflectometry (OFDR) system is divided into the following four main components, including 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 test module 70 .

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

[0081] The maximum detection bandwidths of the first balanced photodetector 406, the second balanced photodetector 507 and the third balanced photodetector 508 are all 200 MHz;

[0082] The sampling frequency of 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 the present invention adopts a Michelson interferometer structure, so its arm length difference is 500m. The optical fiber used is a standard single-mode optical fiber with a refractive index of 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 optical fiber sensitive ring 702 to be tested is connected to the second port of the second circulator 503, and the first Bragg grating 701 is connected at the entrance of the optical fiber sensitive ring; at the same time, the second Bragg grating 703 is connected at the exit of the optical fiber sensitive ring to mark the pigtail position of the optical fiber sensitive ring to be tested;

[0086] The specific implementation method of the geometric symmetry test method of the optical fiber sensitive ring under the temperature field of the present invention is as follows: the optical frequency domain distributed optical fiber sensitive ring characteristic parameter test sensor system is as follows: Figure 3As shown, the continuous frequency sweeping light emitted by the light source 301 is divided into two beams by the first coupler 302, 99% of the light is injected into the main interferometer 5, and the second coupler 501 in the main interferometer 5 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 optical fiber sensitive ring 702 to be tested is connected to the second port of the second circulator 503, and 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 signal that characterizes the phase noise and compensation of the light source. The beat 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 and the third balanced photodetector 508 and the first balanced photodetector 406, respectively, and then data is collected by the acquisition card 601, and finally sent to the computer 602 for subsequent processing of the signal using the method described in the present invention. In order to obtain the full-temperature geometric symmetry evaluation index of the optical fiber sensitive ring to be tested under temperature field excitation.

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

[0088] Step 1 101: First, the temperature field for the optical fiber sensitive ring test needs to be configured to meet the temperature field full-temperature test conditions described in the method;

[0089] Step 2 102: Use a high-performance optical frequency domain reflectometry system to measure distributed characteristic parameters of the optical fiber sensitive ring in the temperature field;

[0090] Step 3 103: According to the full temperature test requirements, several representative specific temperature points in the temperature field are selected for subsequent testing;

[0091] Step 4 104: performing multi-parameter simultaneous decoupling processing on the temperature and strain parameters in the distributed characteristic parameters obtained by the high-performance optical frequency domain reflectometry system test;

[0092] Step five 105: Demodulating the distributed characteristic parameters to obtain the temperature variation of the optical fiber sensitive ring under the temperature field;

[0093] Step 6 106: demodulating the high-performance OFDR test data to obtain the thermal strain generated by the optical fiber sensitive ring under the temperature field;

[0094] Step 7 107: Distributed temperature and strain characteristic parameter data of the optical fiber sensitive ring obtained by multi-parameter decoupling, and the refractive index change under thermal strain The calculation formula is:

[0095]

[0096] in, is the standard refractive index, and is the photoelastic coefficient, is the axial thermal strain, is the thermo-optical coefficient of the optical fiber, and the calculation results of the refractive index change of the optical fiber sensitive ring under the temperature field are as follows: Figure 4 As shown;

[0097] Step eight 108: performing a polarization crosstalk test on the optical fiber sensitive ring to be tested under the temperature field;

[0098] Step 9 109: The radial stress of the optical fiber sensitive ring under the temperature field is obtained by converting the polarization crosstalk test data, and the refractive index change make corrections;

[0099] Step ten 110: dividing the data according to the length of each layer of the measured optical fiber sensitive ring;

[0100] Step 111: performing symmetry analysis of each layer / turn of the divided optical fiber sensitive ring under the temperature field;

[0101] Step 12 112: Firstly, the turn symmetry analysis of the sensitive loop is performed, and a layer of optical fiber data on a symmetrical length needs to be taken as a test unit;

[0102] Step 13 113: Secondly, the layer symmetry analysis of the sensitive ring is performed, and the number of layers of a winding pole on the symmetrical length needs to be taken as a test unit;

[0103] Step 14 114: Input the detection light signal output by the high-performance OFDR test system into the fiber sensitive ring in the clockwise direction. The clockwise (CW) incident light in the fiber sensitive ring is disturbed by the external temperature at point s in the fiber sensitive ring, resulting in a refractive index change. , resulting in a positive phase difference;

[0104] Step 15: Input the detection light signal output by the high-performance OFDR test system into the fiber sensitive ring in the counterclockwise direction. The counterclockwise (CCW) incident light in the fiber sensitive ring will also have a refractive index change at Ls. , but a negative phase difference is produced;

[0105] Step 16 116: Therefore, different refractive index changes are generated on the symmetrical length. By comparing the refractive index changes generated by the CW light and the CCW light, the refractive index change parameters of point s and point Ls are subtracted. , and the asymmetric distribution of the refractive index is obtained The calculation results are shown in the attached Figure 5 shown.

[0106] Step 17 117: Asymmetric refractive index distribution The calculation formula is:

[0107]

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

[0109] Step 19 119: The cumulative distribution result of the asymmetric refractive index of the test unit along the length of the optical fiber can be obtained as shown in the attached figure. Figure 6 As shown;

[0110] Step 20 120: Integrate the cumulative distribution result of the asymmetric refractive index along the length of the optical fiber along the length;

[0111] Step 21 121: 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 hexadecanopole fiber sensitive ring is selected as the test device, L is the total length of the fiber sensitive ring, and m is half of the number of layers of the measured fiber sensitive ring, where m=32. The final calculated full-unit asymmetric refractive index result is shown in the attached figure. Figure 7 As shown;

[0114] Step 22 122: Determine whether the asymmetric refractive index of all test units of the optical fiber ring under the temperature point has been completed. If there are still units that have not completed the calculation of the asymmetric refractive index, then execute the relevant operations of step 23 123. If the asymmetric refractive index of all test units at this temperature point has been completed, , then execute the related operations of step twenty-four 124;

[0115] Step 23 123: When the previous test unit has an asymmetric refractive index When the calculation is completed and it is not the last test unit of the test optical fiber sensitive ring, switch to the next test unit and repeat the relevant operations from step 11 to step 22 until the asymmetric refractive index of all test units of the optical fiber sensitive ring is completed. Calculation of

[0116] Step 24 124: when the cycle is finished, the calculation of the asymmetric refractive index of all the test units on the test optical fiber sensitive ring has been completed, and the asymmetric refractive index of all the units of the tested optical fiber sensitive ring under the excitation of the temperature field is obtained;

[0117] Step 25 125: Accumulating the asymmetric refractive index of all test units on the optical fiber sensitive ring;

[0118] Step 26 126: Obtaining the equivalent asymmetric refractive index , It indicates the overall geometric symmetry of the measured optical fiber sensitive ring, which directly reflects the winding quality of the optical fiber sensitive ring. The calculation formula is:

[0119]

[0120] 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 operations of step 28, if the temperature point of this test is the last specific temperature point in the set full temperature test, execute the relevant operations of step 29;

[0121] Step 28 128: Change the temperature point of the temperature field, and repeat all steps from step 5 to step 27 127 and related operations;

[0122] Step 29: Traverse all temperature points set in the temperature field and obtain the equivalent asymmetric refractive index at each temperature point After that, the full-temperature equivalent asymmetric refractive index of the optical fiber sensitive ring to be tested can be obtained. ;

[0123] Step 30 130: performing an outlier analysis on the full-temperature equivalent asymmetric refractive index of the optical fiber sensitive ring to be tested under the excitation of the temperature field;

[0124] Step 31 131: Calculate the standard deviation of the full-temperature equivalent asymmetric refractive index under temperature field excitation;

[0125] Finally, the geometric symmetry evaluation results of the overall optical fiber sensitive ring are obtained, as shown in the attached figure. Figure 8 shown.

Claims

1. A method for measuring the geometric symmetry of an optical fiber sensitive ring under a temperature field. The method first requires the construction of a high-performance OFDR test system to test the distributed characteristic parameter (temperature and strain) data of the optical fiber sensitive ring, and calculate the refractive index variable of the winding body based on this data, and then perform layer turn symmetry analysis; the method for measuring the geometric symmetry of an optical fiber sensitive ring under a temperature field is characterized in that: The method comprises the following steps: Step 1 (101): First, the temperature field of the optical fiber sensitive ring test needs to be configured to meet the temperature field full-temperature test conditions described in the method; Step 2 (102): Use a high-performance optical frequency domain reflectometry system to measure distributed characteristic parameters of the optical fiber sensitive ring in the temperature field; Step 3 (103): According to the full temperature test requirements, select several representative specific temperature points in the temperature field for subsequent testing; Step 4 (104): performing multi-parameter simultaneous decoupling processing on the temperature and strain parameters in the distributed characteristic parameters obtained by the high-performance optical frequency domain reflectometry system test; Step five (105): Demodulating the distributed characteristic parameters to obtain the temperature variation of the optical fiber sensitive ring under the temperature field; Step 6 (106): Demodulating the high-performance OFDR test data can obtain the thermal strain generated by the optical fiber sensitive ring under the temperature field; Step 7 (107): Distributed temperature and strain characteristic parameter data of the optical fiber sensitive ring obtained by multi-parameter decoupling, and the refractive index change under the action of the temperature field The calculation formula is: in, is the standard refractive index, and is the photoelastic coefficient, is the axial thermal strain, is the thermo-optical coefficient of the optical fiber; Step eight (108): performing a polarization crosstalk test on the optical fiber sensitive ring to be tested under the temperature field; Step 9 (109): The radial stress of the optical fiber sensitive ring under the temperature field is obtained by converting the polarization crosstalk test data, and the refractive index change make corrections; Step ten (110): dividing the data according to the length of each layer of the measured optical fiber sensitive ring; Step 11 (111): performing symmetry analysis of each layer / turn of the divided optical fiber sensitive ring under the temperature field; Step 12 (112): First, a turn symmetry analysis is performed on the sensitive loop, and a layer of optical fiber data on a symmetrical length is taken as a test unit; Step 13 (113): Secondly, the layer symmetry analysis of the sensitive ring is performed, and the number of layers of a winding pole on the symmetrical length needs to be taken as a test unit; Step 14 (114): The detection light signal output by the high-performance OFDR test system is input into the optical fiber sensitive ring in the clockwise direction. The clockwise (CW) incident light in the optical fiber sensitive ring is subjected to external temperature disturbance at point s in the optical fiber sensitive ring, resulting in a refractive index change. , resulting in a positive phase difference; Step 15 (115): Input the detection light signal output by the high-performance OFDR test system into the fiber sensitive ring in the counterclockwise direction. The counterclockwise (CCW) incident light in the fiber sensitive ring will also have a refractive index change at Ls. , but a negative phase difference is produced; Step 16 (116): Therefore, different refractive index changes are generated on the symmetrical length. By comparing the refractive index changes generated by CW light and CCW light, the refractive index change parameters of point s and point Ls are subtracted. , and the asymmetric distribution of the refractive index is obtained . Step 17 (117): wherein the asymmetric refractive index distribution The calculation formula is: Step 18 (118): accumulating the asymmetric refractive index distribution data of the test unit along the length; Step 19 (119): the cumulative distribution result of the asymmetric refractive index of the test unit along the length of the optical fiber can be obtained; Step 20 (120): Integrate the cumulative distribution result of the asymmetric refractive index along the length of the optical fiber along the length; Step 21 (121): After integration, the asymmetric refractive index of the test unit is obtained. , and its calculation formula is: In the formula, 16 indicates that a hexadecanopole optical fiber sensitive ring is selected as the test device, L is the total length of the optical fiber sensitive ring, and m is half of the number of layers of the measured optical fiber sensitive ring, where m=32; Step 22 (122): Determine whether the asymmetric refractive index of all test units of the optical fiber ring under the temperature point has been completed. If there are still units that have not completed the calculation of the asymmetric refractive index, then execute the relevant operations of step 23 (123). If the asymmetric refractive index of all test units at this temperature point has been completed, , then execute the relevant operations of step twenty-four (124); Step 23 (123): When the asymmetric refractive index of the previous test unit When the calculation is completed and it is not the last test unit of the test optical fiber sensitive ring, switch to the next test unit and repeat the relevant operations of step 11 (111) to step 22 (122) until the asymmetric refractive index of all test units of the optical fiber sensitive ring is completed. Calculation of Step 24 (124): When the cycle is completed, the calculation of the asymmetric refractive index of all the test units on the test optical fiber sensitive ring has been completed, and the asymmetric refractive index of all the units of the tested optical fiber sensitive ring under the excitation of the temperature field is obtained; Step 25 (125): Accumulating the asymmetric refractive index of all test units on the optical fiber sensitive ring; Step 26 (126): Obtaining the equivalent asymmetric refractive index , It indicates the overall geometric symmetry of the measured optical fiber sensitive ring, which directly reflects the winding quality of the optical fiber sensitive ring. The calculation formula is: 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 operations of step 28 (128). If the temperature point of this test is the last specific temperature point in the set full temperature test, execute the relevant operations 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 related operations; Step 29 (129): Traverse all temperature points set in the temperature field and obtain the equivalent asymmetric refractive index at each temperature point After that, the full-temperature equivalent asymmetric refractive index of the optical fiber sensitive ring to be tested can be obtained. ; Step 30 (130): performing an outlier analysis on the full-temperature equivalent asymmetric refractive index of the optical fiber sensitive ring to be tested under temperature field excitation; Step 31 (131): Calculate the standard deviation of the full-temperature equivalent asymmetric refractive index under temperature field excitation; Finally, the geometric symmetry evaluation result of the overall optical fiber sensitive ring is obtained.

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