Method for improving precision of fiber-optic gyroscope based on double lithium niobate waveguides

Abstract

The invention relates to the technical field of navigation, and discloses a method for improving the precision of a fiber-optic gyroscope based on double lithium niobate waveguides, and the double lithium niobate waveguides are combined to suppress the intensity noise of a light path system; the RIN power spectrum density after superposition of the two paths of light reaches a minimum value when the light intensity of the main light path is consistent with that of the reference light path in a mode of enabling the light power returned to the photoelectric detector by the main light path and the reference light path to be consistent; the loss of the optical path system is controlled to match the loss change of the sensitive optical fiber ring and stabilize the relative intensity suppression effect of the optical path system. The method adapts to different initial losses and environment changes, and overcomes the defect that a traditional RIN suppression method often adopts a fixed parameter or a single compensation means.

Description

Technical Field

[0001] The present invention relates to the field of navigation technology, and in particular to a method for improving the accuracy of a fiber optic gyroscope based on a lithium diniobate waveguide. Background Art

[0002] Fiber optic gyroscopes measure angular velocity based on the Sagnac effect. They have the advantages of no moving parts, shock resistance, long life and high precision. They are widely used in inertial navigation, attitude control, autonomous driving and other fields.

[0003] To improve gyro accuracy, fiber optic gyros (FOGs) typically use high-power ASE light sources to suppress coherent noise in the gyro's optical path. As ASE light source power increases, relative intensity noise (RIN), generated by random fluctuations in the light source's intensity, becomes the primary noise source in FOGs. Suppressing this RIN is crucial to further improve gyro bias stability.

[0004] Relative intensity noise (RIN) originates from photon statistical fluctuations and light source power fluctuations, and is one of the key factors limiting the accuracy of fiber optic gyroscopes (especially low-frequency noise).

[0005] like Figure 1 As shown in Figure 1, the relative intensity noise is typically reduced by increasing the modulation depth of the gyro system and reducing the optical power reaching the detector. However, due to the presence of thermal noise, the total noise exhibits a V-shaped curve as the modulation depth increases, increasing the total noise and decreasing the gyro zero accuracy. Further increasing the modulation depth does not further suppress the intensity noise.

[0006] On the other hand, when the modulation depth of the gyro system increases, the Y waveguide, the actuator that increases the modulation depth, deteriorates at large modulation depth due to its own waveform slope and 2π reset error performance, resulting in the deterioration of the gyro's output scale factor performance at large modulation depth, especially the reduction of scale factor symmetry.

[0007] Therefore, in order to obtain high gyro accuracy and scaling performance, the gyro is usually designed to operate at point A. At this time, the modulation depth is not deep, so the intensity noise cannot be suppressed and the gyro accuracy cannot be improved.

[0008] like Figure 2As shown in the figure, to further improve gyro accuracy, relative intensity noise must be suppressed, shifting the operating point from point A to point B. For high-precision fiber gyros, the length of the fiber loop is limited by the winding process, resulting in variations in fiber loop length, leading to inconsistent loop loss. Furthermore, loop loss can also vary when affected by ambient temperature. These variations in loop loss lead to changes in the overall optical path loss and, consequently, relative intensity noise. Relative intensity noise suppression techniques that fix optical path device parameters, such as increasing the modulation depth and fixing it at a specific value, significantly reduce their effectiveness.

[0009] Therefore, in practice, there is an urgent need for a method that can perform adaptive adjustments based on the different fiber optic rings and different usage environments, so as to improve the accuracy of the fiber optic gyroscope. Summary of the Invention

[0010] The present invention aims to solve at least one of the technical problems existing in the related art. To this end, the present invention provides a method for improving the accuracy of a fiber optic gyroscope based on a lithium diniobate waveguide.

[0011] A method for improving the accuracy of fiber optic gyroscope based on lithium niobate waveguide. S1: Split the initial light generated by the light source into two beams, one entering the main optical path and the other entering the reference optical path. The light entering the main optical path passes through the first waveguide and a sensitive optical fiber ring in sequence to form a main optical path signal carrying angular rate information and light source intensity noise; the light entering the reference optical path passes through the second waveguide to form a reference optical path signal carrying light source intensity noise. S2, combining the main optical path signal and the reference optical path signal to generate a detection signal representing the optical power of the two signals; S3, based on the detection signal, dynamically adjusting the first waveguide and / or the second waveguide to adjust the optical power of the main optical path signal and / or the reference optical path signal until the optical power of the main optical path signal is consistent with that of the reference optical path signal, thereby suppressing the light source intensity noise; The second waveguide is adjusted to compensate for the difference in loss of the main optical path caused by different gyro models.

[0012] Furthermore, the second waveguide is a lithium niobate straight waveguide, and the second waveguide is controlled by a controller for adjustment.

[0013] Further, the first waveguide is adjusted to compensate for changes in optical path loss of the main optical path caused by changes in ambient temperature; The first waveguide is a lithium niobate Y waveguide, and the first waveguide is controlled by a controller for adjustment.

[0014] Furthermore, the step of adjusting the first waveguide includes: Measuring the ambient temperature of the sensitive optical fiber ring to obtain temperature data; Determining the drift of the optical power of the main optical path according to a preset temperature-optical path loss model and the temperature data; Based on the drift amount, the controller generates a compensation voltage and applies it to the first waveguide to stabilize the optical power of the main optical path signal.

[0015] Furthermore, step S1 also includes: A rotating reflector is further provided in the reference optical path. After passing through the second waveguide, the light in the reference optical path is reflected by the rotating reflector and passes through the second waveguide again.

[0016] Furthermore, the rotating reflector is a 45° Faraday rotating reflector, which rotates the polarization direction of the input light by 90° and outputs the light, thereby realizing fast-slow axis conversion.

[0017] Furthermore, a temperature sensor is used to measure the ambient temperature of the sensitive optical fiber ring and output temperature data to the controller; The controller outputs a control signal to the lithium niobate Y-waveguide based on the temperature data to compensate for changes in optical path loss of the main optical path caused by temperature changes.

[0018] Furthermore, step S1 further includes, Broad-spectrum light is generated by an ASE light source, and the broad-spectrum light is divided into a main light path and a reference light path using a polarization-maintaining fiber beam splitter, which are transmitted to the main light path and the reference light path, respectively. The polarization-maintaining fiber beam splitter includes a fiber polarizer and a 50:50 semi-transparent and semi-reflective membrane to improve the extinction ratio and achieve optical path distribution; the 50:50 semi-transparent and semi-reflective membrane ensures that the incident light of the ASE light source does not directly enter the photodetector, and realizes the optical path connection between the main light path and the reference light path.

[0019] Furthermore, the main optical path signal and the reference optical path signal are received by a photodetector.

[0020] The above one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects: Lithium niobate Y-waveguides and straight lithium niobate waveguides are used to dynamically adjust the optical power of the main and reference optical paths to accommodate varying initial losses and environmental variations. This overcomes the drawbacks of traditional RIN suppression methods, which often rely on fixed parameters or a single compensation method. Compared to methods that suppress RIN solely by increasing the modulation depth, this solution introduces a reference optical path for noise cancellation, supplemented by modulation depth optimization. This theoretically avoids the thermal noise limitations and scale factor degradation issues of traditional methods.

[0021] This solution offers strong engineering practicality and adaptability by adjusting the Y-waveguide voltage in real time based on temperature changes to stabilize the optical power in the main optical path. Furthermore, it adjusts the straight waveguide parameters to match initial loss according to different gyro models (and fiber lengths). Compared to fixed-parameter RIN suppression technologies, this solution, through dynamic adjustment of the dual waveguides, is more adaptable to changes in optical path loss, thereby maintaining a stable suppression effect.

[0022] Based on the existing fiber optic gyroscope RIN suppression technology, this technical solution proposes a more adaptable and potentially better performance solution through an innovative lithium niobate waveguide structure and dynamic compensation strategy, which is highly creative.

[0023] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 This is a graph showing the relationship between traditional noise and modulation depth of a fiber optic gyroscope; Figure 2 is the noise curve of the fiber optic gyroscope after relative intensity noise suppression; Figure 3 This is the optical path structure diagram of the double lithium niobate waveguide high-precision fiber optic gyroscope proposed in the present invention; Figure 4 1 is a structural diagram of the polarization-maintaining optical fiber beam splitter used in the present invention; Figure 5 This is a typical optical fiber ring loss and temperature relationship curve of the present invention; Figure 6 This is a comparison chart of the suppression effect of the double lithium niobate waveguide high-precision fiber optic gyroscope of the present invention. DETAILED DESCRIPTION

[0026] To make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Obviously, the embodiments described are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0027] The present invention aims to solve the problem that high-precision fiber optic gyroscopes cannot improve gyroscope accuracy due to the presence of relative intensity noise in the optical path system caused by the use of a high-power ASE light source. To this end, the present invention proposes: using a double lithium niobate waveguide to jointly suppress the intensity noise of the optical path system; controlling the loss of the optical path system to match the change in loss of the sensitive optical fiber ring, and stabilizing the relative intensity suppression effect of the optical path system.

[0028] like Figure 3 FIG. 1 shows the optical path structure of the double lithium niobate waveguide high-precision fiber optic gyroscope proposed in the present invention.

[0029] This solution adopts a double lithium niobate waveguide structure, which includes a main optical path and a reference optical path.

[0030] Main optical path: ASE light source – polarization-maintaining fiber beam splitter – lithium niobate Y-waveguide – sensitive fiber ring – lithium niobate Y-waveguide – polarization-maintaining fiber beam splitter – photodetector. This optical path is used to sense angular rate.

[0031] Reference optical path: ASE light source – polarization-maintaining fiber beam splitter – lithium niobate straight waveguide – rotating reflector – lithium niobate straight waveguide – polarization-maintaining fiber beam splitter – photodetector. This optical path returns a portion of the light source's RIN.

[0032] RIN suppression, by making the optical powers returned to the photodetector from the signal and reference optical paths consistent, can theoretically enable the RIN power spectral density of the superimposed two light paths to reach a minimum value of 0 under specific conditions (B=1, i.e., the signal and reference light intensities are consistent).

[0033] Dynamic optical power matching uses a lithium niobate straight waveguide (such as a Mach-Zehnder electro-optical modulator) to adjust the optical power of the reference optical path to match the initial optical path loss differences caused by fiber rings of different lengths or fixed reflectors. A lithium niobate Y-waveguide is used to adjust the optical power of the main optical path. By monitoring temperature changes and adjusting the modulation voltage of the Y-waveguide in real time according to a preset temperature-optical path loss model, the modulation voltage is adjusted in real time to compensate for changes in fiber ring loss caused by ambient temperature changes, thereby maintaining stable optical power in the signal optical path.

[0034] Lithium niobate Y-waveguide and lithium niobate straight waveguide are used to control the optical power of the main optical path and reference optical path respectively.

[0035] Polarization-maintaining fiber beam splitter: It consists of a fiber polarizer and a 50:50 semi-transparent and semi-reflective membrane to ensure the extinction ratio of the signal light path and the reference light path, and realize the optical path connection in a specific direction.

[0036] Rotating reflector: A 45° Faraday rotating reflector is used to rotate the input light by 90° and output it, thereby realizing fast-slow axis conversion and improving the extraction efficiency of the RIN signal in the reference optical path.

[0037] The details are as follows: 1. Optical path composition and working process The optical path system of the method for improving the accuracy of fiber optic gyroscope based on double lithium niobate waveguide consists of the following components: ASE light source, polarization-maintaining fiber beam splitter, lithium niobate Y waveguide, lithium niobate straight waveguide, sensitive fiber ring, rotating reflector and photodetector.

[0038] It can be further divided into a main optical path and a reference optical path. The main optical path is sensitive to the angular rate input from the gyroscope, while the reference optical path returns a portion of the relative intensity noise of the light source. The reference optical path and the main optical path are subtracted to suppress the relative intensity noise.

[0039] Composition of the main optical path and signal light transmission process: The light generated by the ASE light source passes through the polarization-maintaining fiber beam splitter and enters the lithium niobate Y waveguide. After the lithium niobate Y waveguide splits the light, it enters the sensitive fiber ring. The positive and negative light beams propagating in the sensitive fiber ring return to the lithium niobate Y waveguide. The lithium niobate Y waveguide and the sensitive fiber ring form a Sagnac interferometer, which is sensitive to external angular velocity. The light enters the polarization-maintaining fiber beam splitter from the lithium niobate Y waveguide and finally enters the photodetector.

[0040] Reference optical path composition and reference light transmission process: The light generated by the ASE light source passes through the polarization-maintaining fiber beam splitter, enters the lithium niobate straight waveguide, enters the rotating reflector, and after reflection, passes through the lithium niobate straight waveguide again, enters the polarization-maintaining fiber beam splitter, and finally enters the photodetector.

[0041] It is particularly important to note that the polarization-maintaining fiber beam splitter consists of a fiber polarizer and a 50:50 semi-transparent and semi-reflective membrane. Figure 4 As shown, the ASE light source is connected to end 1, end 2 is connected to the lithium niobate Y waveguide, end 3 is connected to the lithium niobate straight waveguide, and end 4 is connected to the photodetector.

[0042] The polarizer is used to improve the extinction ratio of the signal light path and the reference light path; the semi-transparent and semi-reflective film is used to ensure that the incident light at end 1 cannot enter the detector end at end 4, and from the perspective of port 4, port 3 is the reflected light end of its incident light, and port 2 is its transmitted light end, ensuring the interconnection between port 3 and port 4, and port 2 and port 3, thereby ensuring the connectivity of the aforementioned signal light path and reference light path.

[0043] The rotating reflector is composed of a 45° Faraday selective reflector. Through 45° rotation, the light input to the rotating reflector is finally rotated 90° and output. That is, the light input from the fast axis and propagating through the rotating reflector is converted into the slow axis output after entering the rotating reflector.

[0044] The lithium niobate straight waveguide is designed and constructed by a lithium niobate thin film waveguide. The lithium niobate thin film waveguide mainly uses the high refractive index difference between lithium niobate and the surrounding materials to achieve a limiting effect on light waves. It has low polarization dependence, but the lithium niobate thin film waveguide has a high light intensity modulation efficiency.

[0045] The principle of relative intensity noise suppression in the solution adopted by the present invention is described as follows: The relative intensity noise power spectral density can be expressed as: (1) Where: is the light source input intensity noise, B is the ratio of the signal light intensity to the reference light intensity, is the light frequency, t is the time, unit is s.

[0046] It can be seen from the formula that the phase intensity noise after the superposition of the two beams of polarization perpendicular to the signal light and the reference light produces a cosine-shaped periodic oscillation compared with the previous one. (2) When B=1, the relative intensity noise power spectral density after superposition reaches a minimum value, and when B=1, that is, the signal light and the reference light have the same intensity and power, the relative intensity noise after superposition of the two beams will be zero at the minimum value; where n is a natural number, taking values ​​1, 2, 3, ...

[0047] Therefore, by ensuring that the optical powers of the signal light and the reference light returning to the photoelectric detection are consistent, the relative intensity noise of the fiber optic gyroscope optical path system takes a minimum value of 0.

[0048] On the one hand, the optical path loss of the fiber optic gyroscope optical system, especially the sensitive fiber ring, will change when the external ambient temperature changes, resulting in changes in the signal optical path loss and the optical power of the signal optical path. Therefore, in order to ensure that the optical power of the reference optical path is consistent with that of the signal optical path, it is necessary to modulate the optical power of the signal optical path or the optical power of the reference optical path accordingly.

[0049] On the other hand, due to the different lengths of the sensitive loops of high-precision fiber optic gyros with different accuracies, or the fact that the lengths of the sensitive loops of high-precision fiber optic gyros with the same accuracy cannot be strictly consistent due to process problems, the loss of the entire high-precision fiber optic gyroscope optical path system is also different. In particular, the fiber loop lengths of high-precision fiber optic gyros with different accuracies can range from 3000 meters to 10,000 meters. If calculated based on a 0.5dB loss per 1000 meters of optical fiber, the optical path loss differs by 3.5dB. This loss difference is very large. If the optical power of the signal optical path and the reference optical path is not matched and adjusted, the relative intensity noise suppression will be ineffective. The traditional matching method is to adjust the reflectivity of the reflector, which requires the production of a series of reflectors with different reflectivities. The reflector with the appropriate reflectivity is selected for assembly during the optical path assembly. Since the reflectivity of the reflector is fixed, there will be a large matching error when matching the optical power.

[0050] The present invention adopts a double lithium niobate waveguide, jointly controls the voltage at both ends of the double lithium niobate waveguide, and adjusts the optical power of the signal optical path and the reference optical path in real time to make them equal, thereby achieving the best intensity noise suppression effect.

[0051] Traditionally, large modulation depths degrade the scale factor performance. However, the use of straight waveguides to eliminate the relative intensity noise of the Y-waveguide avoids the large modulation depth of the Y-waveguide.

[0052] Example 1 The deviation of different types of fiber optic gyroscope systems is adjusted using straight waveguides: Using two fiber optic gyroscopes with fiber lengths of 3000 meters and 10000 meters, and setting the modulation depth of the lithium niobate Y waveguide to 2π / 3, the overall optical path loss of the signal optical path is calculated: The optical path loss of the gyroscope signal using 3000 meters of optical fiber is as follows: polarizer 3dB + beam splitter 3dB + lithium niobate Y-waveguide 3dB + optical fiber ring 1.5dB + optical path melting point and device loss 6.5dB, with an overall optical path loss of 17dB. After modulation, the overall optical path loss reaching the detector end is about 32dB; the additional 15dB is the loss of the lithium niobate Y-waveguide when the modulation depth is 2π / 3.

[0053] The optical path loss of the gyro signal using 10,000 meters of optical fiber is as follows: 3dB for the polarizer, 3dB for the beam splitter, 3dB for the lithium niobate Y-waveguide, 5dB for the fiber ring, and 6.5dB for the optical path melting point and device loss, for a total optical path loss of 20.5dB. After modulation, the total optical path loss reaching the detector is approximately 35.5dB. The additional 15dB is the loss of the lithium niobate Y-waveguide at a modulation depth of 2π / 3.

[0054] Calculate the loss value that needs to be adjusted for the lithium niobate straight waveguide in the reference optical path when the reflectivity of the fixed reflector is 5% (13dB).

[0055] 3000 meters: 32dB - polarizer 3dB - beam splitter 3dB - reflector 13dB - optical path melting point and device loss 3dB = 10dB.

[0056] 10,000 meters: 35.5dB - polarizer 3dB - beam splitter 3dB - reflector 13dB - optical path melting point and device loss 3dB = 13.5dB.

[0057] When a Mach-Zehnder electro-optic modulator is used in a lithium niobate straight waveguide and a symmetrical double lithium niobate crystal structure is designed, the refractive index change after applying a voltage to the modulator electrodes will cause a change in the intensity of the interference light, which can change the loss value of the reference optical path and control it at 10dB and 13.5dB, respectively. This makes the optical power of the signal optical path and the reference optical path consistent, and both models of fiber optic gyroscopes achieve relative intensity noise suppression effects.

[0058] Example 2 The environmental deviation of the fiber optic gyroscope system is adjusted using a Y-waveguide. When the fiber optic gyroscope is in environmental fluctuations, the depth and deviation of adjustment using a straight waveguide are large, while a Y-waveguide is used to adjust for small fluctuations in environmental changes.

[0059] When the external environment changes, the signal optical path loss where the sensitive ring is located will change. By establishing a temperature and optical path loss model and modifying the voltage of the lithium niobate Y waveguide to adjust the optical power of the signal optical path, the optical power of the signal optical path can be kept consistent when the temperature changes.

[0060] Typical optical fiber ring loss and temperature relationship curve, such as Figure 5 As shown, it can be simply fitted as: (3) Where: P is the optical path loss, K is the proportional coefficient, and T is the temperature.

[0061] The relationship between the modulation voltage and output power of lithium niobate Y waveguide is: (4) Where: is the output optical power, is the input lithium niobate Y waveguide optical power, V is the modulation voltage, is the modulated π voltage.

[0062] Combining (3) and (4), we have (5) As can be seen from Equation 5, measuring the temperature T of the signal light path and adjusting the modulation voltage V of the lithium niobate Y waveguide in real time according to Equation (5) can ensure the stability of the optical power of the signal light path.

[0063] The typical fiber length is 3000 meters. The FOG-3000 uses a double lithium niobate waveguide. The relative intensity noise suppression effect is as follows: Figure 6 shown.

[0064] Closed-loop control strategy: Measure the current main optical path optical power Ps and the reference optical path optical power Pr; Calculate the difference ΔP = Ps - Pr; The control system adjusts the voltage of the lithium niobate straight waveguide according to ΔP to make ΔP→0; by setting the maximum adjustment amount ΔP of the lithium niobate Y waveguide Y Avoid excessive noise introduction caused by excessive adjustment depth of the Y waveguide.

[0065] At the same time, the temperature T is measured; based on the typical fiber ring loss and temperature relationship curve, the bias voltage of the lithium niobate Y waveguide is fine-tuned to pre-compensate for the drift of Ps caused by the temperature change of the fiber ring, reduce the pressure of reference optical path tracking, and help maintain the Y waveguide working in a better modulation state.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for improving the accuracy of a fiber optic gyroscope based on a lithium niobate waveguide, characterized in that: S1: Split the initial light generated by the light source into two beams, one entering the main optical path and the other entering the reference optical path. The light entering the main optical path passes through the first waveguide and a sensitive optical fiber ring in sequence to form a main optical path signal carrying angular rate information and light source intensity noise; the light entering the reference optical path passes through the second waveguide to form a reference optical path signal carrying light source intensity noise. S2, combining the main optical path signal and the reference optical path signal to generate a detection signal representing the optical power of the two signals; S3, based on the detection signal, dynamically adjusting the first waveguide and / or the second waveguide to adjust the optical power of the main optical path signal and / or the reference optical path signal until the optical power of the main optical path signal is consistent with that of the reference optical path signal, thereby suppressing the light source intensity noise; The second waveguide is adjusted to compensate for the difference in loss of the main optical path caused by different gyro models.

2. The method for improving the accuracy of a fiber optic gyroscope based on a lithium niobate waveguide according to claim 1, characterized in that: The second waveguide is a lithium niobate straight waveguide, and the second waveguide is controlled by a controller for adjustment.

3. The method for improving the accuracy of a fiber optic gyroscope based on a double lithium niobate waveguide according to claim 1, characterized in that: Adjusting the first waveguide to compensate for changes in optical path loss of the main optical path caused by changes in ambient temperature; The first waveguide is a lithium niobate Y waveguide, and the first waveguide is controlled by a controller for adjustment.

4. The method for improving the accuracy of a fiber optic gyroscope based on a double lithium niobate waveguide according to claim 3, characterized in that: The step of adjusting the first waveguide comprises: Measuring the ambient temperature of the sensitive optical fiber ring to obtain temperature data; Determining the drift of the optical power of the main optical path according to a preset temperature-optical path loss model and the temperature data; Based on the drift amount, the controller generates a compensation voltage and applies it to the first waveguide to stabilize the optical power of the main optical path signal.

5. The method for improving the accuracy of a fiber optic gyroscope based on a double lithium niobate waveguide according to claim 1, characterized in that: The S1 step also includes: A rotating reflector is further provided in the reference optical path. After passing through the second waveguide, the light in the reference optical path is reflected by the rotating reflector and passes through the second waveguide again.

6. The method for improving the accuracy of a fiber optic gyroscope based on a double lithium niobate waveguide according to claim 5, characterized in that: The rotating reflector is a 45° Faraday rotating reflector, which rotates the polarization direction of the input light by 90° and outputs the light, thereby realizing fast-slow axis conversion.

7. The method for improving the accuracy of a fiber optic gyroscope based on a double lithium niobate waveguide according to claim 3, characterized in that: A temperature sensor is used to measure the ambient temperature of the sensitive optical fiber ring and output temperature data to the controller; The controller outputs a control signal to the lithium niobate Y-waveguide based on the temperature data to compensate for changes in optical path loss of the main optical path caused by temperature changes.

8. The method for improving the accuracy of a fiber optic gyroscope based on a double lithium niobate waveguide according to claim 1, characterized in that: The S1 step further comprises, Broad-spectrum light is generated by an ASE light source, and the broad-spectrum light is divided into a main light path and a reference light path using a polarization-maintaining fiber beam splitter, which are transmitted to the main light path and the reference light path, respectively. The polarization-maintaining fiber beam splitter includes a fiber polarizer and a 50:50 semi-transparent and semi-reflective membrane to improve the extinction ratio and achieve optical path distribution; the 50:50 semi-transparent and semi-reflective membrane ensures that the incident light of the ASE light source does not directly enter the photodetector, and realizes the optical path connection between the main light path and the reference light path.

9. The method for improving the accuracy of a fiber optic gyroscope based on a double lithium niobate waveguide according to claim 1, characterized in that: The main optical path signal and the reference optical path signal are received by a photoelectric detector.

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