Differential method for forecasting thermally induced null drift of fiber-optic gyroscope

Abstract

The invention provides a differential method for forecasting thermally induced null drift of a fiber-optic gyroscope, and belongs to the technical field of fiber-optic gyroscopes and optical measurement. The method is characterized in that a polarization-maintaining OFDR multi-parameter decoupling technology is utilized to detect temperature variation and thermal strain of an optical fiber sensitive ring in a dynamic temperature change process; the method comprises the following steps of: calculating a refractive index variation, firstly making a difference between the refractive index variation along a clockwise direction and the refractive index variation along an anticlockwise direction according to the obtained refractive index variation, calculating asymmetric refractive index distribution, and then performing integral calculation along the length of an optical fiber to obtain a full-temperature gyroscope angle deviation result. And deriving to obtain a total-temperature gyroscope null drift forecasting result. According to the method, the zero drift of the gyroscope system can be quantitatively and accurately forecasted by testing the optical path of the optical fiber ring of the optical fiber gyroscope through the OFDR, and compared with a traditional gyroscope system zero drift method, the method is high in testing speed and forecasting precision, can be used for quantitative zero drift optimization and online zero drift compensation of the gyroscope system, and plays an important role in improving the performance of the gyroscope system.

Description

Technical Field

[0001] The patented method belongs to the field of fiber optic gyroscope and optical measurement technology, and in particular relates to a differential method for predicting thermally induced zero drift of a fiber optic gyroscope. Background Art

[0002] Fiber optic gyroscope is a non-mechanical angular velocity measuring instrument based on Sagnac effect invented in the 1970s. Among them, interferometric fiber optic gyroscope (IFOG) has the characteristics of low cost, small size, light weight, low power consumption, fast startup, large dynamic range, strong corrosion and noise resistance, high sensitivity, good working stability and high reliability. Interferometric fiber optic gyroscope can accurately measure the angular velocity and angular acceleration of an object. According to the measurement results, the motion state, trajectory, direction of travel and other information of the object can be obtained through calculation, so it has an important position and huge application value in the fields of aerospace, military, and sensing.

[0003] As an interferometric sensor, the internal interferometer of the fiber optic gyroscope is affected by many environmental factors, which is a common problem. For example, temperature changes, stress effects, and external shocks will affect the performance of the fiber optic gyroscope (such as the thermal drift and scale factor of the gyroscope). In the actual operation of the fiber optic gyroscope, when the internal heating and the change of ambient temperature are applied to a section of optical fiber in the fiber sensitive ring, it will cause temperature disturbance, and then produce a non-reciprocal phase shift, which is indistinguishable from the phase shift caused by the rotational attitude, so that the fiber optic gyroscope will produce a large drift error, affecting the output accuracy of the fiber optic gyroscope.

[0004] In order to improve the measurement accuracy and zero drift of fiber optic gyroscopes, Yang Zhihuai, Ma Lin and others from the 707th Institute of China Shipbuilding Industry Corporation proposed a fiber optic gyroscope temperature coefficient test and compensation method (CN 201610623262.2), which extracted the temperature gradient coefficient of the fiber optic gyroscope at different temperature points, and realized the temperature compensation of zero drift through the post-processing method of logic chips such as FPGA. Liu Yuanyuan and others from Beijing Aerospace Times Optoelectronics Technology Co., Ltd. disclosed a fiber optic gyroscope temperature error modeling method based on parameter uncertainty (CN202310218468.7), which effectively solved the contradiction between the applicability and accuracy of the model and could realize the temperature error compensation of high-precision fiber optic gyroscopes. Ren Yongjia and others from Nankai University disclosed a fiber optic gyroscope low-temperature shock error compensation method (CN202310170514.0), which used LSTM neural network to model the temperature characteristics of the fiber optic gyroscope, overcoming the problem that the traditional linear model cannot model the nonlinear part of the temperature drift. Chen Liqing and others from East China Normal University disclosed a machine learning-assisted fiber optic gyroscope polarization locking and slow drift compensation system and method (CN202310502448.2). The system can intelligently search and predict the relationship between the fiber optic gyroscope interference error signal and the polarization direction of the incident light by introducing neural networks in machine learning, and feed back the predicted optimal value to the hardware system for compensation, thereby realizing the function of fiber polarization locking and suppressing the intensity slow drift of the output signal. However, the above work is mainly based on artificial intelligence methods such as machine learning, which requires a large amount of test data as a priori conditions, lacks analysis of the output bias analytical model of the fiber optic gyroscope, and is difficult to predict the thermally induced zero drift of the fiber optic gyroscope.

[0005] In 2020, Liu Junhao and Li Ruichen from the 46th Institute of China Electronics Technology Group Corporation published a paper (Analysis of thermal drift in high performance interferometric fiber-optic gyroscopes). They established an analytical model of the output bias of the fiber gyroscope, which for the first time considered the influence of fiber birefringence and directly linked the gyroscope performance to the mechanical, thermal, optical and geometric parameters of the fiber. The model shows that the high birefringence of polarization-maintaining fiber and its temperature fluctuations are the main error sources of thermal drift in interferometric fiber gyroscopes. In 2024, Leng Yue and Zhong Sheng from Huazhong University of Science and Technology published a paper (Thermal-Induced Drift Analysis and Algorithm Compensation Technology of Fiber Optic Gyroscope). Through the analysis and derivation of the temperature drift of the fiber optic gyroscope, they analyzed the deep-seated reasons for the gyroscope drift error caused by temperature disturbances, and combined with the process correlation theory, verified and analyzed the correlation between the influencing factors of each temperature term and the actual output of the fiber optic gyroscope, and proposed an algorithmic compensation model that simultaneously considers temperature, temperature change rate, temperature gradient and the product coupling terms of the three. However, the above work is limited by the performance of the test instrument and the test method. There is only one temperature sensor placed inside the fiber optic gyroscope, which can only obtain the temperature of the surface of the fiber optic ring body. It is also impossible to achieve fully distributed high-precision and accurate measurement of the thermally induced zero drift of the fiber optic gyroscope.

[0006] Optical frequency shift reflection (OFDR) based on Rayleigh scattering is widely used in sensing research for pressure, temperature and strain measurement because of its characteristics of easy distributed sensing detection and high-precision measurement. In 2022, Jérémie Pillon and others from Paris-Saclay University published a paper (Thermomechanical analysis of the effects of homogeneous thermal fieldinduced in the sensing coil of a fiber-optic gyroscope). They used finite element simulation to briefly describe the thermal strain characteristics of the fiber-optic sensitive ring, proposed a new method for estimating thermal drift based on the thermal strain of the fiber-optic sensitive ring, and analyzed the influence of OFDR system accuracy on the calculation accuracy of thermal drift. In 2023, Yang Jun's research team from Guangdong University of Technology published a paper (Zero drift of gyroscope in variable temperature using high accuracy distributed strain of km-level fiber coil). They used the self-developed OFDR to test a 3 km fiber-optic sensitive ring, successfully calculated the thermal drift of the fiber-optic sensitive ring and analyzed the influence of spatial resolution on the calculation accuracy. Therefore, OFDR technology can be applied to high-precision distributed testing of optical fiber sensitive rings, and the obtained thermal strain can be used for optical symmetry analysis and the development of analytical methods for thermally induced drift. Summary of the invention

[0007] 1. A differential method for predicting thermally induced zero drift of an optical fiber gyroscope, characterized in that the method comprises the following steps:

[0008] 1) Step S1: Use polarization-maintaining OFDR multi-parameter tester to test the optical fiber sensitive ring under temperature change;

[0009] 2) Step S2: Decoupling the temperature variation and thermal strain of the optical fiber sensitive ring using multi-parameter decoupling technology;

[0010] 3) Step S3: Calculate the asymmetric refractive index distribution by subtracting the refractive index change in the clockwise direction from the refractive index change in the counterclockwise direction;

[0011] 4) Step S4: By segmenting the optical fiber sensitive ring and integrating along the length, the gyro angle deviation under full temperature conditions is output, and then the full-temperature gyro thermal zero drift is predicted by derivation.

[0012] 2. A differential method for predicting thermally induced zero drift of an optical fiber gyroscope according to claim 1, characterized in that the specific process of using polarization-maintaining OFDR to perform multi-parameter testing in step S1 is:

[0013] 1) placing the fiber optic gyroscope module (42) to be tested inside the temperature box (41) to keep the four sides of the fiber optic sensitive ring (423) evenly heated;

[0014] 2) Do not start the temperature box (41) first, and keep the temperature of the temperature box (41) consistent with the normal temperature;

[0015] 3) Use the polarization-maintaining OFDR multi-parameter tester to test the optical fiber sensitive ring;

[0016] 4) In the polarization-maintaining OFDR multi-parameter tester, the backward Rayleigh scattered light returned by the fiber optic gyro module (42) to be tested forms a beat frequency signal in the interferometer sensor arm module (3), which is respectively divided into orthogonal signals of the P polarization state and the S polarization state by the polarization-maintaining beam splitter 1 (305) and the polarization-maintaining beam splitter 2 (306), and differential detection is performed using the balanced photodetector 2 (307) and the balanced photodetector 3 (308), and the collected signals are recorded as the normal temperature reference signals of the P polarization state and the S polarization state;

[0017] Starting the incubator (41), setting the temperature change range of the incubator (41) to -40°C to 70°C, and setting the temperature change rate to 1°C / min; performing a temperature change test every 5 minutes using a polarization-maintaining OFDR multi-parameter tester;

[0018] 6) The signals collected during the variable temperature test are recorded as variable temperature test signals of the P polarization state and the S polarization state.

[0019] 3. A differential method for predicting thermally induced zero drift of an optical fiber gyroscope according to claim 1, characterized in that the specific method for decoupling the temperature variation and the thermal strain in step S2 is:

[0020] 1) First, perform Fourier transform on the reference signals of the P polarization state and S polarization state at room temperature, then intercept their spectrum data, align the positions, and perform inverse Fourier transform. The spectrum offset before heating is obtained through correlation. ; Then perform Fourier transformation on the collected P polarization state and S polarization state temperature-varying test signals, intercept their spectrum data, align the positions, and then perform inverse Fourier transformation, and obtain the spectrum offset after heating through correlation. ,Will minus Get the autocorrelation frequency shift ; Then, the collected P polarization state normal temperature reference signal and P polarization state variable temperature test signal are Fourier transformed, and then the spectrum data is intercepted, the position is aligned, and then the inverse Fourier transform is performed to obtain the cross-correlation spectrum offset through correlation ;

[0021] 2) During the temperature change test, there are temperature changes and thermal strain changes inside the optical fiber sensitive ring (423). , cross-correlation frequency shift , Autocorrelation frequency shift temperature coefficient , Cross-correlation frequency shift temperature coefficient , autocorrelation frequency shift strain coefficient and cross-correlation frequency shift strain coefficient The temperature and strain relationship matrix composed is used to perform multi-parameter decoupling of temperature variation and thermal strain;

[0022] (1)

[0023] 3) After , , and After calibration of the four decoupling coefficients, and Substituting into the temperature-strain decoupling matrix, the temperature change under variable temperature and the thermal strain data under variable temperature are obtained simultaneously.

[0024] 4. A differential method for predicting thermally induced zero drift of an optical fiber gyroscope according to claim 1, characterized in that the specific method for calculating the asymmetric refractive index distribution in step S3 is:

[0025] 1) The light entering the optical fiber sensitive ring (423) is divided into two interference lights propagating in the clockwise direction and the counterclockwise direction at the injection point. They pass through the same length of When the closed optical fiber loop is The temperature is disturbed, and the phase error is:

[0026] (2)

[0027] Fiber Refractive Index And the fiber length The expressions that vary with temperature are:

[0028] (3)

[0029] (4)

[0030] in, is the refractive index of the fiber core, and is the elastic-optical coefficient of the optical fiber, , and They are the strains in radial direction (interlayer direction), axial direction (interturn direction) and positive direction (along the optical fiber direction), is the Poisson’s ratio of the fiber core;

[0031] Combining formula (3) and formula (4) to get the refractive index change The expression is:

[0032] (5)

[0033] The first term in formula (5) represents the refractive index change caused by strain. The strain generated by the optical fiber sensitive ring (423) at 1°C is about 8με. is 0.27, is 0.121, is 1.456, Poisson's ratio is 0.186, so the refractive index change of the optical fiber sensitive ring (423) caused by strain at 1°C is 1×10 -6 ; The second term indicates that the length change caused by strain at 1°C is 1×10 -6 , the third term is the refractive index change caused by temperature, and the thermo-optical coefficient is 1.2×10 -5 ; Therefore, the refractive index change caused by temperature at 1°C is 1×10 -5 The refractive index change caused by temperature is the main cause of the phase difference. , Relative to axial strain is one to two orders of magnitude smaller, so the lateral strain , The influence of can be ignored. It can be approximated as:

[0034] (6)

[0035] 2) The light propagating in the clockwise direction in the optical fiber sensitive ring (423) is incident at the point The temperature at the incident point is disturbed by the external environment, resulting in a change in the refractive index, which leads to a positive phase difference. Similarly, the light propagating in the counterclockwise direction is There will also be a refractive index change at the point, resulting in a negative phase difference. Therefore, different refractive index changes are produced on the symmetrical length. By subtracting the point and Point The refractive index variation parameter is used to obtain the asymmetric distribution of the refractive index. :

[0036] (7)

[0037] 5. A differential method for predicting thermally induced zero drift of an optical fiber gyroscope according to claim 1, characterized in that the specific method for calculating the thermally induced zero drift of the gyroscope under full temperature conditions in step S4 is:

[0038] 1) dividing the optical fiber sensitive ring (423) into N units according to the spatial resolution, wherein the value of N is the optical fiber length / spatial resolution / 2;

[0039] 2) The asymmetric refractive index corresponding to the optical fiber sensitive ring (423) of each unit Multiplying the corresponding length on the optical fiber sensitive ring (423) to calculate the optical path change;

[0040] 3) integrating the optical path change of the optical fiber sensitive ring (423) of each unit along the length of the optical fiber, calculating the angle deviation, and then accumulating and summing the angle deviations of all units;

[0041] 4) outputting the final accumulated angle deviation value of the optical fiber sensitive ring (423);

[0042] 5) Repeat the above steps to calculate the angle deviation at different temperature points, and output the angle deviation results of the fiber optic gyroscope ring at all temperatures;

[0043] 6) Derivative the output full-temperature angle deviation result, and output the full-temperature thermally induced zero drift result of the optical fiber sensitive ring (423):

[0044] (8)

[0045] in, represents the length of a spatial resolution, Indicates the length of the fiber ring. is the average diameter of the fiber ring.

[0046] The present invention provides a differential method for predicting thermally induced zero drift of an optical fiber gyroscope. The method utilizes the multi-parameter decoupling technology of a polarization-maintaining OFDR tester to detect the temperature variation and thermal strain of an optical fiber sensitive ring during a dynamic temperature change process, and adopts a special differential method to quantitatively predict the distributed zero drift in a long-distance optical fiber gyroscope under a rapid temperature change field.

[0047] 1. The device of polarization-maintaining OFDR multi-parameter tester is as shown in the attached Figure 1 As shown, it comprises a light source module (1), an interferometer reference arm module (2), an interferometer sensor arm module (3), a variable temperature test module (4), and a data acquisition and processing module (5), and is characterized in that:

[0048] 1) The light source module (1) is connected to the interferometer reference arm module (2) via a flange 1 (201);

[0049] 2) The interferometer reference arm module (2) and the interferometer sensor arm module (3) are connected via a flange 3 (301);

[0050] 3) The variable temperature test module (4) and the interferometer sensor arm module (3) are connected via a flange 4 (401);

[0051] 4) The data acquisition and processing module (5) and the interferometer reference arm module (2) are connected via an electrical conductor 1 (501), and the data acquisition and processing module (5) and the interferometer sensor arm module (3) are connected via an electrical conductor 2 (502) and an electrical conductor 3 (503).

[0052] 2. The above-mentioned light source module (1) is characterized in that:

[0053] 1) The light source module (1) is composed of a TSL light source (101).

[0054] 3. The interferometer reference arm module (2) is characterized by:

[0055] 1) The interferometer reference arm module (2) is composed of a flange 1 (201), a polarization-maintaining optical fiber (202), a polarizer (203), a coupler 1 (204), a flange 2 (205), a single-mode optical fiber (206), a circulator 1 (207), a coupler 2 (208), a delay optical fiber (209), a Faraday rotator 1 (210), a Faraday rotator 2 (211) and a balanced photodetector 1 (212);

[0056] 2) The polarization-maintaining optical fiber (202) is connected to the TSL light source (101) via the flange 1 (201);

[0057] 3) The output upper arm of the coupler 1 (204) is connected to the interferometer sensor arm module (3) through the flange 3 (301);

[0058] 4) The output lower arm of the coupler 1 (204) is connected to the single-mode optical fiber (206) through the flange 2 (205);

[0059] 5) The circulator 2 (207) is divided into two paths through the coupler 2 (208), the output upper arm of the coupler 2 (208) is connected to the Faraday rotator 1 (210), and the output lower arm of the coupler is connected to the Faraday rotator 2 (211) through the delay optical fiber (209); the reflected light enters the balanced detector 1 (212) through the coupler 2 (208) and beats with the reflected light of the circulator 2 (207).

[0060] 4. The interferometer sensor arm module (3) is characterized by:

[0061] 1) The interferometer sensor arm module (3) is composed of a flange 3 (301), a coupler 3 (302), a circulator 2 (303), a coupler 4 (304), a polarization-maintaining beam splitter 1 (305), a polarization-maintaining beam splitter 2 (306), a balanced detector 2 (307) and a balanced detector 3 (308);

[0062] 2) The output light of the lower arm of the coupler 3 (302) is connected to the fiber optic gyro module (4) to be tested through the circulator 2 (303), and the backward Rayleigh scattered light is connected to the coupler 4 (304) through the circulator 2 (303);

[0063] 3) The upper arm of the coupler (302) outputs the transmitted light and is connected to the coupler 4 (304);

[0064] 4) The two output light beams of coupler 4 (304) pass through polarization-maintaining beam splitter 1 (305) and polarization-maintaining beam splitter 2 (306) respectively to split the beat frequency light into orthogonal polarized light of P polarization state and S polarization state, and enter balanced detector 2 (307) and balanced detector 3 (308) respectively for differential detection.

[0065] 5. The above-mentioned variable temperature test module (4) is characterized by:

[0066] 1) The variable temperature test module (4) is composed of a temperature box (41) and a fiber optic gyroscope module (42) to be tested. The temperature change range of the temperature box (41) is -40°C to 70°C, and the temperature change rate is 1°C / min;

[0067] 2) The fiber optic gyroscope module (42) to be tested is composed of an input pigtail (421), an output pigtail (422) and a fiber optic sensitive ring (423);

[0068] 3) The input pigtail (421) is connected to the interferometer sensor arm module (3) through the flange 4 (401), and the right side is connected to the optical fiber sensitive ring (423). The right side of the optical fiber sensitive ring (423) is connected to the output pigtail (422).

[0069] 6. The above-mentioned data acquisition and processing module (5) is characterized by:

[0070] 1) The data acquisition and processing module (5) is composed of a data acquisition card (504), a host computer (506), a serial port cable (505), an electrical conductor 1 (501), an electrical conductor 2 (502) and an electrical conductor 3 (503);

[0071] 2) The data acquisition card (504) is connected to the balanced detector 1 (212) via the electrical conductor 1 (501). The data acquisition card (504) is connected to the balanced detector 2 (307) via the electrical conductor 2 (502); The data acquisition card (504) is connected to the balanced detector 3 (308) via the electrical conductor 3 (503);

[0072] 3) The data acquisition card (504) is connected to the host computer via a serial port cable (505).

[0073] The process of configuring the full temperature test environment is as follows: Figure 3 As shown, its characteristics are:

[0074] As can be seen from step (411), firstly, a device is selected, a temperature box (41) having a full temperature change range of -40°C to 70°C is selected, and the temperature change rate of the temperature box (41) is set to 1°C / min;

[0075] As can be seen from step (412), after setting the system parameters of the temperature box (41), the corresponding components are connected according to the component connection method, the fiber optic gyroscope module (42) to be tested is placed inside the temperature box (41), the fiber optic sensitive ring (423) is kept heated on all four sides, and the temperature change debugging of the fiber optic gyroscope module (42) to be tested is started;

[0076] As can be seen from step (413), the first step of debugging is to adjust the temperature of the incubator (41) to 25°C and keep it warm for 30 minutes;

[0077] As can be seen from step (414), the second step is to cool the temperature of the incubator (41) from 25°C to -40°C at a temperature change rate of 1°C / min;

[0078] As can be seen from step (415), the third step is to keep the temperature of the incubator (41) at -40°C for 60 minutes;

[0079] As can be seen from step (416), the fourth step is to increase the temperature of the incubator (41) from -40°C to 70°C at a temperature change rate of 1°C / min;

[0080] As can be seen from step (417), the fifth step is to keep the temperature of the incubator (41) at 70°C for 60 minutes;

[0081] It can be seen from step (418) that, in the process of adjusting the ambient temperature of the temperature box (41), the multi-parameter optical frequency domain tester tests the fiber optic gyroscope module (42) to be tested once every 5 minutes, thereby completing the full temperature test.

[0082] Compared with the prior art, the advantages of the present invention are:

[0083] 1. A differential method for output angle deviation and zero drift prediction of fiber optic gyro system based on gyro optical path level distributed test is proposed;

[0084] 2. The differential method has fast zero drift test speed and high prediction accuracy, and establishes the quantitative transfer relationship between optical frequency shift, temperature and thermal strain, refractive index change, output angle deviation of fiber optic gyroscope and zero drift distribution;

[0085] 3. The differential method of zero drift prediction can be used for quantitative zero drift optimization and online zero drift compensation of the gyro system. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] Figure 1 This is a diagram of the polarization-maintaining OFDR multi-parameter tester setup;

[0087] Figure 2 This is a flow chart of the differential method for predicting thermally induced zero drift of fiber optic gyroscope;

[0088] Figure 3 This is the full-temperature test flow chart of thermally induced zero drift of fiber optic gyroscope;

[0089] Figure 4 This is a schematic diagram of calculating the change in refractive index of the optical fiber sensitive ring;

[0090] Figure 5 This is a schematic diagram of calculating the asymmetric refractive index difference of the optical fiber sensitive ring;

[0091] Figure 6 This is a schematic diagram of the accumulation of thermally induced drift along the length of the optical fiber sensitive ring;

[0092] Figure 7 This is the calculation result diagram of the angle deviation of the optical fiber sensitive ring under full temperature conditions;

[0093] Figure 8 This is the calculation result diagram of the thermal drift of the optical fiber sensitive ring under full temperature conditions; DETAILED DESCRIPTION

[0094] In order to clearly explain the thermally induced zero drift differential prediction method of the fiber optic gyroscope of the present invention, the following Figure 4 , Attachment Figure 5 , Attachment Figure 6 , Attachment Figure 7 and attached Figure 8 The present invention is further described, but the protection scope of the present invention should not be limited thereto.

[0095] A fiber sensitive ring (423) with a length of 3 km was selected and connected to the polarization-maintaining OFDR multi-parameter test device for temperature change test. The temperature of the fiber sensitive ring (423) was adjusted by the temperature box (41), the temperature change rate was set to 1°C / min, the spatial resolution was 5cm, and the light source frequency scanning range was 10nm. Figure 4As shown, based on multi-parameter decoupling, the temperature and thermal strain data are obtained and put into formula (6) to calculate the refractive index change Next, find the midpoint of the length of the fiber sensitive ring (423) and convert the refractive index change Divided into the refractive index change along the clockwise direction and the refractive index change in the counterclockwise direction . Then, as attached Figure 5 As shown in the figure, by using formula (7), the refractive index change along the clockwise direction is and the refractive index change in the counterclockwise direction Make a difference and get the asymmetric refractive index variation coefficient Finally, as attached Figure 6 As shown, the thermally induced drift accumulated along the length at the end of the optical fiber sensitive ring (423) is calculated by formula (8).

[0096] Through the above analysis, the thermal drift of the gyroscope at a single temperature point is obtained. Next, the fiber optic sensitive ring (423) is placed in a temperature chamber (41) for a rapid temperature change experiment. The temperature chamber (41) initially maintains an initial temperature of 20°C. After the temperature is stabilized for 20 minutes, the temperature is gradually lowered to about -40°C at a rate of 1°C / min and maintained at a low temperature of -40°C for 40 minutes. Then, the fiber optic sensitive ring (423) is heated to 70°C at a temperature rate of 1°C / min, and the experiment is completed after being maintained at this high temperature of 70°C for 40 minutes. During the rapid temperature change experiment, the fiber optic sensitive ring (423) is tested every 5 minutes. The predicted rotation angle deviation at all temperatures is shown in the attached figure. Figure 7 As shown in the figure, the dotted line represents the rotation angle deviation, and the solid line corresponds to the temperature change. During the heating process, there is a consistent relationship between the angle deviation and the temperature change. As the temperature changes, the angle deviation accumulates continuously, and the range of the rotation angle deviation at all temperatures is 3.4°. The predicted thermally induced drift at all temperatures is shown in the attached figure. Figure 8 As shown, the dashed line represents thermal drift, and the solid line represents the temperature change rate. It can be seen that the temperature change rate is the direct cause of thermal drift, and the distribution of thermal drift is basically consistent with the temperature change rate. For the 3 km optical fiber sensitive ring (423), the range of thermal drift is 0.33 ° / h.

Claims

1. A differential method for predicting thermally induced zero drift of a fiber optic gyroscope, characterized in that: The method comprises the following steps: 1) Step S1: Use a polarization-maintaining OFDR multi-parameter tester to test the optical fiber sensitive ring under temperature variation; 2) Step S2: Decoupling the temperature variation and thermal strain of the optical fiber sensitive ring using multi-parameter decoupling technology; 3) Step S3: Calculate the asymmetric refractive index distribution by subtracting the refractive index change in the clockwise direction from the refractive index change in the counterclockwise direction; 4) Step S4: By segmenting the optical fiber sensitive ring and integrating along the length, the gyro angle deviation under full temperature conditions is output, and then the full-temperature gyro thermal zero drift is predicted by derivation.

2. A differential method for predicting thermally induced zero drift of an optical fiber gyroscope according to claim 1, characterized in that: The specific process of using polarization-maintaining OFDR to perform multi-parameter testing in step S1 is as follows: 1) placing the fiber optic gyroscope module (42) to be tested inside a temperature box (41) to keep the four sides of the fiber optic sensitive ring (423) evenly heated; 2) Do not start the thermostat (41) first, and keep the temperature of the thermostat (41) consistent with normal temperature; 3) Use the polarization-maintaining OFDR multi-parameter tester to test the optical fiber sensitive ring; 4) In a polarization-maintaining OFDR multi-parameter tester, the backward Rayleigh scattered light returned by the fiber optic gyroscope module (42) to be tested forms a beat frequency signal in the interferometer sensor arm module (3), which is respectively divided into orthogonal signals of the P polarization state and the S polarization state by the polarization-maintaining beam splitter 1 (305) and the polarization-maintaining beam splitter 2 (306), and differential detection is performed using the balanced photodetector 2 (307) and the balanced photodetector 3 (308), and the collected signals are recorded as normal temperature reference signals of the P polarization state and the S polarization state; 5) starting the incubator (41), setting the temperature change range of the incubator (41) to -40°C to 70°C, and setting the temperature change rate to 1°C / min; performing a temperature change test every 5 minutes using a polarization-maintaining OFDR multi-parameter tester; 6) The signals collected during the variable temperature test are recorded as variable temperature test signals of the P polarization state and the S polarization state.

3. A differential method for predicting thermally induced zero drift of an optical fiber gyroscope according to claim 1, characterized in that: The specific method for decoupling the temperature variation and thermal strain in step S2 is: 1) First, perform Fourier transform on the collected reference signals of P polarization state and S polarization state at room temperature, then intercept their spectrum data, align the positions, and perform inverse Fourier transform. The spectrum offset v before heating is obtained through correlation. a1 ; Then perform Fourier transform on the collected P polarization state and S polarization state temperature-varying test signals and intercept their spectrum data, perform position alignment, and then perform inverse Fourier transform, and obtain the spectrum offset v after heating through correlation a2 , v a1 Subtract v a2 Get the autocorrelation frequency shift v a ; Then, the collected P polarization state normal temperature reference signal and P polarization state variable temperature test signal are Fourier transformed, and then the spectrum data is intercepted, the position is aligned, and then the inverse Fourier transform is performed, and the cross-correlation spectrum offset v is obtained by correlation. c ; 2) During the temperature change test, there are temperature changes and thermal strain changes inside the optical fiber sensitive ring (423). According to the autocorrelation frequency shift v a , cross-correlation frequency shift v c , Autocorrelation frequency shift temperature coefficient T a , Cross-correlation frequency shift temperature coefficient T c , autocorrelation frequency shift strain coefficient ε a and the cross-correlation frequency shift coefficient ε c The temperature and strain relationship matrix composed is used to perform multi-parameter decoupling of temperature variation and thermal strain; 3) After T a 、T c , ε a and ε c After calibration of the four decoupling coefficients, v c and v a Substituting into the temperature-strain decoupling matrix, the temperature change under variable temperature and the thermal strain data under variable temperature are obtained simultaneously.

4. A differential method for predicting thermally induced zero drift of an optical fiber gyroscope according to claim 1, characterized in that: The specific method for calculating the asymmetric refractive index distribution in step S3 is: 1) The light entering the optical fiber sensitive ring (423) is divided into two interference lights propagating in the clockwise direction and the counterclockwise direction at the injection point. When they pass through the closed optical fiber loop with the same length L, the length δ s The temperature is disturbed, and the phase error is: d(δφ)=(2π / λ0)·δ s ·dn+(2π / λ0)·n·dδ s (2) Fiber refractive index n and fiber length δ s The expressions that vary with temperature are: Where n0 is the refractive index of the fiber core, p 11 and p 12 is the elastic-optical coefficient of the optical fiber, ε r , ε z and ε θ are the strains in radial direction (interlayer direction), axial direction (interturn direction) and normal direction (along the fiber direction), respectively, and μ is the Poisson’s ratio of the fiber core; Combining formula (3) and formula (4) to get the refractive index change α T The expression is: The first term in formula (5) represents the refractive index change caused by strain. The strain generated by the optical fiber sensitive ring (423) at 1°C is about 8με. 11 is 0.27, p 12 =0.121, n0 = 1.456, and Poisson's ratio μ = 0.

186. Therefore, the refractive index change caused by strain at 1°C in the optical fiber sensitive ring (423) is 1×10 -6 ; The second term indicates that the length change caused by strain at 1°C is 1×10 -6 , the third term is the refractive index change caused by temperature, and the thermo-optical coefficient is 1.2×10 -5 ; Therefore, the refractive index change caused by temperature at 1°C is 1×10 -5 The refractive index change caused by temperature is the main cause of the phase difference. r , ε z Relative to the axial strain ε θ is one to two orders of magnitude smaller, so the lateral strain ε r , ε z The influence of α can be ignored. T It can be approximated as: 2) The light propagating in the clockwise direction in the optical fiber sensitive ring (423) is disturbed by the external temperature at the incident point s, resulting in a refractive index change, which leads to a positive phase difference. Similarly, the light propagating in the counterclockwise direction also experiences a refractive index change at the incident point Ls, resulting in a negative phase difference. Therefore, different refractive index changes are generated on the symmetrical length: a Ts =a T (s,T)-a T (Ls,T) (7) By subtracting the refractive index variation parameters at point s and point Ls, the asymmetric distribution of the refractive index α is obtained. Ts .

5. A differential method for predicting thermally induced zero drift of an optical fiber gyroscope according to claim 1, characterized in that: The specific method for calculating the gyro thermally induced zero drift under full temperature conditions in step S4 is: 1) dividing the optical fiber sensitive ring (423) into N units according to the spatial resolution, wherein the value of N is the optical fiber length / spatial resolution / 2; 2) The asymmetric refractive index α corresponding to the optical fiber sensitive ring (423) of each unit Ts Multiplying the corresponding length on the optical fiber sensitive ring (423) to calculate the optical path change; 3) Integrate the optical path change of the optical fiber sensitive ring (423) of each unit along the length of the optical fiber, calculate the angle deviation, and then accumulate and sum the angle deviations of all units; 4) Outputting the final accumulated angle deviation value of the optical fiber sensitive ring (423); 5) Repeat the above steps to calculate the angle deviation at different temperature points, and output the angle deviation results of the fiber optic gyroscope ring under full temperature conditions; 6) Deriving the output full-temperature angle deviation result, outputting the full-temperature thermally induced zero drift result of the optical fiber sensitive ring (423): Where ds represents the length of a spatial resolution, L represents the fiber ring length, and D is the average diameter of the fiber ring.

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