Differential method for predicting thermal-induced bias of fiber-optic gyroscope

Abstract

This invention provides a differential method for predicting thermally induced zero drift in fiber optic gyroscopes, belonging to the fields of fiber optic gyroscopes and optical measurement technology. Its key features include: utilizing polarization-maintaining OFDR multi-parameter decoupling technology to detect the temperature change and thermal strain of the fiber optic sensing ring during dynamic temperature variations; calculating the refractive index change; based on the obtained refractive index change, first subtracting the refractive index change along the clockwise and counterclockwise directions to calculate the asymmetric refractive index distribution; then integrating along the fiber length to obtain the full-temperature gyroscope angle deviation result; and finally, differentiating to obtain the full-temperature gyroscope zero drift prediction result. This method can achieve quantitative and accurate prediction of gyroscope system zero drift through OFDR testing of the fiber optic ring. Compared with traditional gyroscope system zero drift methods, it offers faster testing speed and higher prediction accuracy, and can be used for quantitative zero drift optimization and online zero drift compensation of gyroscope systems, playing a significant role in improving the performance of gyroscope systems.

Description

Technical Field

[0001] This 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 in fiber optic gyroscopes. Background Technology

[0002] Fiber optic gyroscopes are non-mechanical angular velocity measuring instruments based on the Sagnac effect, invented in the 1970s. Interferometric fiber optic gyroscopes (IFOGs) are characterized by low cost, small size, light weight, and low power consumption. They also feature fast start-up, large dynamic range, strong resistance to corrosion and noise, high sensitivity, good operational stability, and high reliability. IFOGs can accurately measure the angular velocity and angular acceleration of objects. Based on the measurement results, information such as the object's motion state, trajectory, and direction of travel can be calculated. Therefore, they hold an important position and have enormous application value in aerospace, military, and sensing fields.

[0003] As an interferometric sensor, the fiber optic gyroscope is susceptible to numerous environmental factors, such as temperature variations, stress, and external shocks, all of which affect its performance (e.g., thermal drift and scaling factor). During operation, internal heat generation and ambient temperature changes applied to a section of fiber in the sensing loop cause temperature disturbances, resulting in a non-reciprocal phase shift. This non-reciprocal phase shift is indistinguishable from the phase shift caused by rotational attitude, leading to significant drift errors and impacting the gyroscope's output accuracy.

[0004] To improve the measurement accuracy and zero drift of fiber optic gyroscopes, Yang Zhihuai, Ma Lin, and others from the 707 Research Institute of China Shipbuilding Industry Corporation proposed a method for testing and compensating the temperature coefficient of fiber optic gyroscopes (CN 201610623262.2). This method extracts the temperature gradient coefficient of the fiber optic gyroscope at different temperature points and achieves zero drift temperature compensation through post-processing methods using logic chips such as FPGAs. Liu Yuanyuan and others from Beijing Aerospace Times Optoelectronic Technology Co., Ltd. disclosed a method for modeling the temperature error of fiber optic gyroscopes based on parametric uncertainty (CN202310218468.7). This method effectively solves the contradiction between the applicability and accuracy of the model and can achieve high-precision temperature error compensation for fiber optic gyroscopes. Ren Yongjia and others from Nankai University disclosed a method for compensating the low-temperature impact error of fiber optic gyroscopes (CN202310170514.0). This method uses an LSTM neural network to model the temperature characteristics of the fiber optic gyroscope, overcoming the problem that traditional linear models cannot model the nonlinear part of temperature drift. Chen Liqing et al. from East China Normal University disclosed a machine learning-assisted system and method for polarization locking and slow drift compensation of fiber optic gyroscopes (CN202310502448.2). This system, by introducing neural networks from machine learning, can intelligently search and predict the relationship between the fiber optic gyroscope's interference error signal and the polarization direction of the incident light, and feeds back the predicted optimal value to the hardware system for compensation, thereby achieving fiber polarization locking and suppressing the intensity drift of the output signal. However, the above work is mainly based on artificial intelligence methods such as machine learning, requiring a large amount of test data as prior conditions. It lacks analysis of the analytical model of the fiber optic gyroscope's output bias, making it difficult to predict the thermally induced zero drift of the fiber optic gyroscope.

[0005] In 2020, Liu Junhao and Li Ruichen from the 46th Research 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 for the output bias of fiber optic gyroscopes, 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. This model demonstrates that the high birefringence and temperature fluctuations of polarization-maintaining fibers are the main sources of thermal drift error in interferometric fiber optic 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 temperature drift in fiber optic gyroscopes, they analyzed the underlying causes of gyroscope drift error caused by temperature disturbances. Combining process correlation theory, they verified the correlation between various temperature-related factors 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 term of these three factors. However, the above work is limited by the performance of the testing instruments and the testing methods. Only one temperature sensor is placed inside the fiber optic gyroscope, which can only obtain the temperature of the surface of the fiber optic loop. It is not yet possible to achieve fully distributed, high-precision, and accurate measurement of 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 measurements due to its advantages of convenient distributed sensing and high-precision measurement. In 2022, Jérémie Pillon et al. from Paris-Saclay University published a paper (Thermomechanical analysis of the effects of homogeneous thermal field induced in the sensing coil of a fiber-optic gyroscope), which briefly explained the thermal strain characteristics of the fiber optic sensing coil using finite element simulation, proposed a new method for estimating thermally induced drift based on the thermal strain of the fiber optic sensing coil, and analyzed the impact of OFDR system accuracy on the accuracy of thermally induced drift calculation. 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), which tested a 3 km fiber optic sensing coil using a self-developed OFDR, successfully calculated the thermally induced drift of the fiber optic sensing coil, and analyzed the impact of spatial resolution on calculation accuracy. Therefore, OFDR technology can be applied to high-precision distributed testing of fiber optic sensitive loops, 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 in fiber optic gyroscopes, characterized in that the method comprises the following steps:

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

[0009] 2) Step S2: Use multi-parameter decoupling technology to decouple the temperature change and thermal strain of the fiber optic sensing ring;

[0010] 3) Step S3: Calculate the asymmetric refractive index distribution by subtracting the refractive index changes along the clockwise and counterclockwise directions;

[0011] 4) Step S4: By segmenting the fiber sensing ring and integrating along its length, the gyroscope angle deviation under full temperature conditions is output, and then the thermally induced zero drift of the full-temperature gyroscope is predicted by differentiation.

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

[0013] 1) Place the fiber optic gyroscope module (42) to be tested inside the temperature chamber (41) and keep the fiber optic sensing ring (423) evenly heated on all four sides;

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

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

[0016] 4) In the polarization-maintaining OFDR multi-parameter tester, the backscattered Rayleigh light returned by the fiber optic gyroscope module (42) forms a beat frequency signal in the interferometer sensing arm module (3). It is divided into orthogonal signals of P polarization state and S polarization state by polarization beam splitter 1 (305) and polarization beam splitter 2 (306), respectively. Differential detection is performed using balanced photodetector 2 (307) and balanced photodetector 3 (308). The collected signals are recorded as room temperature reference signals of P polarization state and S polarization state.

[0017] Start the temperature chamber (41), set the temperature change range of the temperature chamber (41) to -40℃~70℃, and set the temperature change rate to 1℃ / min; use the polarization-maintaining OFDR multi-parameter tester to perform a temperature change test every 5 minutes.

[0018] 6) Record the signals collected during the temperature change test as temperature change test signals in P polarization state and S polarization state.

[0019] 3. The differential method for predicting thermally induced zero drift of a fiber optic gyroscope according to claim 1, characterized in that the specific method for decoupling the temperature change and thermal strain in step S2 is as follows:

[0020] 1) First, perform Fourier transform on the collected P-polarized and S-polarized room-temperature reference signals, then extract their spectral data, align their positions, and then perform an inverse Fourier transform. The spectral shift before heating is obtained through correlation. Then, after performing Fourier transforms on the acquired temperature-changing test signals in the P-polarization and S-polarization states, their spectral data are extracted, aligned, and then subjected to inverse Fourier transforms. The spectral shift after heating is obtained through correlation. ,Will minus Obtain the autocorrelation frequency shift Subsequently, Fourier transforms were performed on the acquired room-temperature reference signal and the variable-temperature test signal in the P-polarization state. The spectral data were then truncated, aligned, and subjected to an inverse Fourier transform. The cross-correlation spectral shift was obtained through correlation analysis. ;

[0021] 2) During the variable temperature test, both temperature change and thermal strain change exist simultaneously inside the fiber optic sensing loop (423). According to the autocorrelation frequency shift... 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-strain relationship matrix is ​​used to decouple the temperature change and thermal strain through multiple parameters.

[0022] (1)

[0023] 3) After the investigation , , and After calibrating the four decoupling coefficients, and Substituting the temperature-strain decoupling matrix, we can obtain both the temperature change and thermal strain data under varying temperatures.

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

[0025] 1) The light entering the fiber optic sensitive loop (423) is split into two interfering beams at the injection point, one propagating clockwise and the other counterclockwise. They pass through the same length... When the optical fiber loop is closed, the length The phase error caused by temperature disturbance is:

[0026] (2)

[0027] Fiber refractive index and fiber length The expressions for the change with temperature are as follows:

[0028] (3)

[0029] (4)

[0030] in, Let be the refractive index of the fiber core. and This is the elastic optical coefficient of the optical fiber. , and These represent the strains in the radial (interlayer direction), axial (inter-turn direction), and positive (along the fiber direction), respectively. The Poisson's ratio of the fiber core;

[0031] The change in refractive index is obtained by combining formulas (3) and (4). 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 fiber sensing ring (423) at 1℃ is approximately 8με. It is 0.27. It is 0.121. The ratio is 1.456, Poisson's ratio. The value is 0.186. Therefore, the refractive index change caused by strain in the fiber optic sensing ring (423) at 1℃ is 1×10⁻⁶. -6 The second term indicates that the length change caused by strain at 1℃ is 1×10⁻⁶. -6 The third term represents the change in refractive index caused by temperature, with a thermo-optical coefficient of 1.2 × 10⁻⁶. -5 Therefore, the temperature-induced change in refractive index at 1℃ is 1×10⁻⁶. -5 Temperature-induced changes in refractive index are the main cause of phase difference, due to transverse strain. , Relative to axial strain It needs to be one to two orders of magnitude smaller, so the lateral strain , The impact is negligible. It can be approximated as:

[0034] (6)

[0035] 2) The light propagating clockwise within the fiber optic sensitive loop (423) at the incident point An external temperature disturbance causes a change in refractive index, resulting in a positive phase difference. Similarly, light propagating counterclockwise at the point of incidence... There will also be a change in refractive index at a certain point, resulting in a negative phase difference. Therefore, different refractive index changes occur along the symmetrical length. This can be addressed by subtracting the point... and points The refractive index variation parameter was used to obtain the asymmetric distribution of the refractive index. :

[0036] (7)

[0037] 5. The differential method for predicting thermally induced zero drift of a fiber optic 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 as follows:

[0038] 1) Divide the fiber sensing loop (423) into N units according to the spatial resolution, where N is the fiber length / spatial resolution / 2;

[0039] 2) The asymmetric refractive index corresponding to the fiber sensing loop (423) of each unit. Multiply by its corresponding length on the fiber sensing loop (423) to calculate the optical path change;

[0040] 3) Integrate the optical path change of the fiber sensing loop (423) of each unit along the fiber length, calculate the angle deviation, and then sum the angle deviations of all units.

[0041] 4) The final cumulative angle deviation value of the output fiber sensing loop (423);

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

[0043] 6) Differentiate the output full-temperature angle deviation result to obtain the full-temperature thermally induced zero drift result of the output fiber sensing loop (423):

[0044] (8)

[0045] in, Represents the length of a spatial resolution. Indicates the length of the fiber optic loop. It is the average diameter of the fiber optic ring.

[0046] This invention provides a differential method for predicting thermally induced zero drift in fiber optic gyroscopes. It utilizes the multi-parameter decoupling technology of a polarization-maintaining OFDR tester to detect the temperature change and thermal strain of the fiber optic sensing ring during dynamic temperature changes, and employs a specialized differential method to quantitatively predict the distributed zero drift in long-distance fiber optic gyroscopes under rapid temperature change fields.

[0047] 1. The apparatus of the polarization-maintaining OFDR multi-parameter analyzer is shown in the attached figure. Figure 1 As shown, it includes a light source module (1), an interferometer reference arm module (2), an interferometer sensing arm module (3), a variable temperature testing module (4), and a data acquisition and processing module (5), characterized by:

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

[0049] 2) The interferometer reference arm module (2) and the interferometer sensing arm module (3) are connected by flange 3 (301);

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

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

[0052] 2. The light source module (1) described above is characterized by:

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

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

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

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

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

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

[0059] 5) Circulator 2 (207) is split into two paths by coupler 2 (208). The upper output arm of coupler 2 (208) is connected to Faraday rotator 1 (210), and the lower output arm of coupler is connected to Faraday rotator 2 (211) via delay fiber (209). The reflected light beats with the reflected light of circulator 2 (207) through the entry balance detector 1 (212) of coupler 2 (208).

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

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

[0062] 2) The output light from the lower arm of coupler 3 (302) is connected to the fiber optic gyroscope module (4) under test via circulator 2 (303), and the backscattered Rayleigh light is connected to coupler 4 (304) via circulator 2 (303).

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

[0064] 4) The two output beams of coupler 4 (304) are separated into P-polarized and S-polarized beams by polarization-maintaining beam splitter 1 (305) and polarization-maintaining beam splitter 2 (306), respectively, and then enter balanced detector 2 (307) and balanced detector 3 (308) for differential detection.

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

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

[0067] 2) The fiber optic gyroscope module under test (42) consists of an input pigtail (421), an output pigtail (422), and a fiber optic sensing loop (423);

[0068] 3) The input pigtail (421) is connected to the interferometer sensing arm module (3) via flange 4 (401), and its right side is connected to the fiber optic sensing ring (423). The right side of the fiber optic sensing ring (423) is connected to the output pigtail (422).

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

[0070] 1) The data acquisition and processing module (5) consists of a data acquisition card (504), a host computer (506), a serial cable (505), a wire 1 (501), a wire 2 (502), and a wire 3 (503);

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

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

[0073] The procedure for configuring a full-temperature testing environment is attached. Figure 3 As shown, its characteristics are:

[0074] As can be seen from step (411), the first step is to select the device and choose a temperature chamber (41) with a full temperature change range of -40℃ to 70℃. The temperature change rate of the temperature chamber (41) is set to 1℃ / min.

[0075] As can be seen from step (412), after setting the system parameters of the temperature chamber (41), the corresponding devices are connected according to the device connection method, the fiber optic gyroscope module (42) to be tested is placed inside the temperature chamber (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 the debugging is to adjust the temperature of the incubator (41) to 25℃ 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℃ to -40℃ at a temperature change rate of 1℃ / min;

[0078] As can be seen from step (415), the third step is to keep the temperature in the incubator (41) for 60 minutes when the temperature drops to -40℃.

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

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

[0081] As can be seen from step (418), during the process of adjusting the ambient temperature of the temperature chamber (41), the multi-parameter optical frequency domain tester performs a test on the fiber optic gyroscope module (42) under test every 5 minutes; thus completing the full temperature test.

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

[0083] 1. A differential method for predicting output angle deviation and zero drift of a fiber optic gyroscope system based on optical path-level distributed testing of gyroscopes is proposed.

[0084] 2. The differential method has a fast zero-drift test speed and high prediction accuracy, and has established a quantitative transmission 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 gyroscope systems. Attached Figure Description

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

[0087] Figure 2 This is a flowchart of the differential method for predicting thermally induced zero drift in fiber optic gyroscopes;

[0088] Figure 3 This is a flowchart of the full-temperature test procedure for thermally induced zero drift of a fiber optic gyroscope.

[0089] Figure 4 This is a schematic diagram illustrating the calculation of the refractive index change of the fiber optic sensing ring;

[0090] Figure 5 This is a schematic diagram for calculating the asymmetric refractive index difference of the fiber optic sensing loop;

[0091] Figure 6 This is a schematic diagram of the cumulative thermal drift along the length of the fiber optic sensitive loop;

[0092] Figure 7 This is a graph showing the calculated angle deviation of the fiber optic sensing ring under full-temperature conditions;

[0093] Figure 8 The graph shows the calculation results of the thermally induced drift of the fiber optic sensing ring under full temperature conditions. Detailed Implementation

[0094] To clearly illustrate the thermally induced zero-drift differential prediction method using the fiber optic gyroscope of the present invention, in conjunction with the appendix... Figure 4 Appendix Figure 5 Appendix Figure 6 Appendix Figure 7 and attached Figure 8 The present invention will be further described, but this should not be construed as limiting the scope of protection of the present invention.

[0095] A 3km long fiber optic sensing loop (423) was selected and connected to a polarization-maintaining OFDR multi-parameter testing device for temperature variation testing. The temperature of the fiber optic sensing loop (423) was regulated by a temperature chamber (41), with a temperature change rate set to 1℃ / min, a spatial resolution of 5cm, and a light source frequency scanning range of 10nm. (See attached...) Figure 4As shown, temperature and thermal strain data are obtained based on multi-parameter decoupling, and substituted into formula (6) to calculate the refractive index change. Next, locate the midpoint of the length of the fiber sensing loop (423) and measure the change in refractive index. Divided into the change in refractive index along the clockwise direction and the change in refractive index in the counterclockwise direction Subsequently, as attached Figure 5 As shown, the change in refractive index along the clockwise direction is expressed by formula (7). and the change in refractive index in the counterclockwise direction By subtracting, we obtain the coefficient of asymmetric refractive index variation. Finally, as attached. Figure 6 As shown, the thermally induced drift accumulated along the length at the end of the fiber sensing loop (423) is calculated using formula (8).

[0096] Based on the above analysis, the thermally induced drift of the gyroscope at a single temperature point was obtained. Next, the fiber optic sensing ring (423) was placed in a temperature chamber (41) for a rapid temperature change experiment. The temperature chamber (41) was initially maintained at 20°C. After stabilizing for 20 minutes, the temperature was gradually reduced to approximately -40°C at a rate of 1°C / min, and held at -40°C for 40 minutes. Then, the fiber optic sensing ring (423) was heated to 70°C at a rate of 1°C / min and held at this high temperature for 40 minutes to complete the experiment. During the rapid temperature change experiment, the fiber optic sensing ring (423) was tested every 5 minutes. The predicted rotation angle deviation at all temperatures is shown in the attached figure. Figure 7 As shown, the dashed 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; the angle deviation accumulates as the temperature changes, with a range of 3.4° across the entire temperature range. The predicted thermally induced drift across all temperatures is shown in the attached figure. Figure 8 As shown, the dashed line represents thermally induced drift, and the solid line represents the rate of temperature change. It can be seen that the rate of temperature change is the direct cause of thermally induced drift, and the distribution of thermally induced drift is basically consistent with the rate of temperature change. For this 3 km fiber sensing loop (423), the range of thermally induced drift is 0.33 ° / h.

Claims

1. A differential method for predicting thermally induced zero drift in fiber optic gyroscopes, characterized in that, The method includes the following steps: 1) Step S1: Use a polarization-maintaining OFDR multi-parameter tester to test the fiber optic sensitive ring under temperature change conditions; 2) Step S2: Use multi-parameter decoupling technology to decouple the temperature change and thermal strain of the fiber optic sensing ring; 3) Step S3: Calculate the asymmetric refractive index distribution by subtracting the refractive index changes along the clockwise and counterclockwise directions. Specifically, the light entering the fiber optic sensitive loop (423) is split into two interfering beams at the injection point: one propagating clockwise and the other counterclockwise. When these beams pass through the same closed fiber loop of length L, their lengths δ... s The phase error caused by the temperature disturbance is d(δφ): d(δφ)=(2π / λ0)·δ s ·dn+(2π / λ0)·n·dδ s (1) Fiber refractive index n and fiber length δ s The expressions for dn and dδ as a function of temperature T s They are respectively: Where n0 is the refractive index of the fiber core, p 11 and p 12 ε is the elastic optical coefficient of the optical fiber. r ε z and ε θ These represent the strains in the radial interlayer direction, axial inter-turn direction, and positive fiber direction, respectively; μ is the Poisson's ratio of the fiber core; and ΔT is the temperature change. The change in refractive index α is obtained by combining formulas (2) and (3). T The expression is: The first term in formula (4) represents the refractive index change caused by strain. The strain generated by the fiber sensing ring (423) at 1℃ is approximately 8με, p 11 The value is 0.27, p 12 With n = 0.121, n0 = 1.456, and Poisson's ratio μ = 0.186, the refractive index change of the fiber sensing ring (423) caused by strain at 1℃ is 1 × 10⁻⁶. -6 The second term indicates that the length change caused by strain at 1℃ is 1×10⁻⁶. -6 The third term represents the change in refractive index caused by temperature, with a thermo-optical coefficient of 1.2 × 10⁻⁶. -5 Therefore, the temperature-induced change in refractive index at 1℃ is 1×10⁻⁶. -5 Temperature-induced changes in refractive index are the main cause of phase difference, due to transverse strain ε. r ε z Relative to axial strain ε θ It needs to be one to two orders of magnitude smaller, so the transverse strain ε r ε z The effect is negligible, α T It can be approximated as: Light propagating clockwise within the fiber optic sensing loop (423) experiences a refractive index change at the incident point s due to external temperature disturbance, resulting in a positive phase difference. Similarly, light propagating counterclockwise also experiences a refractive index change at the incident point Ls, generating a negative phase difference. Therefore, different refractive index changes occur along the symmetrical length. By subtracting the refractive index change parameters at points s and Ls, the asymmetric distribution α of the refractive index is obtained. Ts : a Ts =a T (s,T)-a T (Ls,T) (6) 4) Step S4: By segmenting the fiber sensing ring and integrating along its length, the gyroscope angle deviation under full temperature conditions is output, and then the thermally induced zero drift of the full-temperature gyroscope is predicted by differentiation.

2. The differential method for predicting thermally induced zero drift of a fiber optic gyroscope according to claim 1, characterized in that, The specific procedure for multi-parameter testing using a polarization-maintaining OFDR in step S1 is as follows: 1) Place the fiber optic gyroscope module (42) to be tested inside the temperature chamber (41) and keep the fiber optic sensing ring (423) evenly heated on all four sides; 2) Do not start the incubator (41) first, and keep the temperature of the incubator (41) consistent with the room temperature; 3) Use a polarization-maintaining OFDR multi-parameter tester to test the fiber optic sensitive ring; 4) In the polarization-maintaining OFDR multi-parameter tester, the backscattered Rayleigh light returned by the fiber optic gyroscope module (42) forms a beat frequency signal in the interferometer sensing arm module (3). It is divided into orthogonal signals of P polarization state and S polarization state by polarization beam splitter 1 (305) and polarization beam splitter 2 (306), respectively. Differential detection is performed using balanced photodetector 2 (307) and balanced photodetector 3 (308). The collected signals are recorded as room temperature reference signals of P polarization state and S polarization state. 5) Start the temperature chamber (41), set the temperature change range of the temperature chamber (41) to -40℃~70℃, and set the temperature change rate to 1℃ / min; use the polarization-maintaining OFDR multi-parameter tester to perform a temperature change test every 5 minutes. 6) Record the signals collected during the temperature change test as temperature change test signals in P polarization state and S polarization state.

3. The differential method for predicting thermally induced zero drift of a fiber optic gyroscope according to claim 1, characterized in that, The specific method for decoupling temperature change and thermal strain in step S2 is as follows: 1) First, perform Fourier transform on the collected P-polarized and S-polarized room-temperature reference signals, then extract their spectral data, align their positions, and then perform an inverse Fourier transform. The spectral shift v before heating is obtained through correlation. a1 Then, after performing Fourier transforms on the acquired temperature-changing test signals in the P-polarization and S-polarization states, their spectral data are extracted, aligned, and then subjected to inverse Fourier transforms. The spectral shift v after temperature rise is obtained through correlation. a2 , will v a1 Subtract v a2 Obtain the autocorrelation frequency shift v a Subsequently, Fourier transforms were performed on the acquired P-polarized state room-temperature reference signal and the P-polarized state variable-temperature test signal. Then, the spectral data was truncated, aligned, and subjected to an inverse Fourier transform. The cross-correlation spectral offset v was obtained through correlation analysis. c ; 2) During the variable temperature test, both temperature change and thermal strain change exist simultaneously inside the fiber optic sensing loop (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 cross-correlation frequency shift strain coefficient ε c The temperature-strain relationship matrix is ​​used to decouple the temperature change and thermal strain through multiple parameters. 3) After studying T a T c ε a and ε c After calibrating the four decoupling coefficients, v c and v a Substituting the temperature-strain decoupling matrix, we obtain both the temperature change ΔT and the thermal strain data Δε under varying temperatures.

4. The differential method for predicting thermally induced zero drift of a fiber optic 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 as follows: 1) Divide the fiber sensing loop (423) into N units according to the spatial resolution, where N is the fiber length / spatial resolution / 2; 2) The asymmetric refractive index α corresponding to the fiber sensing loop (423) of each unit Ts Multiply by its corresponding length on the fiber sensing loop (423) to calculate the optical path change; 3) Integrate the optical path change of the fiber sensing loop (423) of each unit along the fiber length, calculate the angle deviation, and then sum the angle deviations of all units. 4) The final cumulative angle deviation value of the output fiber sensing loop (423); 5) Repeat the above steps to calculate the angle deviation at different temperature points, and output the angle deviation result of the fiber optic gyroscope ring under all temperature conditions; 6) Differentiate the output full-temperature angle deviation result to obtain the full-temperature thermally induced zero drift result of the output fiber sensing 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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