Optical Noise Suppression And Closed Loop Detection Method Of The Circularly Polarized Resonant Fiber Optic Gyroscope

With the rapid development of modern inertial technology,the application requirements of inertial systems for the high-precision and miniaturization of gyroscopes are increasing.In particular,space applications such as spacecraft and micro-satellites have strict requirements on the accuracy,volume,and quality of the gyroscope.Resonant fiber optic gyro(RFOG)equipped with a resonator caters to the development needs of modern inertial technology with its advantages of easy miniaturization,easy integration,and high-precision potential,and has quickly become a research hotspot in the gyro field in recent years.However,there is still a large gap between the reported RFOG laboratory accuracy and theoretical accuracy.This is mainly caused by the optical noise problem in the resonator.The noise problem also increases the complexity of the system signal processing.These problems limit RFOG’s accuracy improvement and practical application.Therefore,an effective method for suppressing intracavity optical noise and corresponding signal processing methods are needed to solve the current problems faced by RFOG.In response to the above-mentioned problems,this subject makes full use of the optical noise suppression characteristics of circularly polarized light resonators,and carries out theoretical research and experimental verification of RFOG based on circularly polarized light transmission resonators from three aspects: circularly polarized light RFOG resonator design,intracavity optical noise suppression and RFOG closed-loop detection method research.The main research contents of this paper are as follows:Aiming at the problem of the current RFOG resonator structure which lacks a good circularly polarized light transmission function,the design method of circularly polarized light transmission resonator has been carried out.Through the analysis of the working principle of RFOG,the sensing characteristics and signal processing characteristics of RFOG are revealed,and combined with the transmission characteristics of circularly polarized light,the advantages of circularly polarized light in the coherent optical noise suppression of RFOG resonator are analyzed.The spun fiber is introduced into the resonator as the transmission medium for circularly polarized light waves,and two /4fiber wave plates with the front and back ends rotating in the same direction at 45°are used to achieve reciprocity single-rotation circularly polarized light.Furthermore,the polarization noise in the cavity is suppressed by introducing a single-polarization fiber.Research has shown that the designed resonator structure can realize the reciprocal transmission of circularly polarized light in a single rotation direction,which has laid an important foundation for subsequent research on the subject.In view of the unclear mechanism of coherent optical noise suppression in the circularly polarized RFOG resonator and the lack of specific and feasible optical noise suppression methods,the research on the intracavity optical noise of the circularly polarized light transmission resonator was carried out.By analyzing the essential causes of the optical noise in the resonator,the principle of the RFOG error caused by the backscattered noise and the optical Kerr effect in the resonator is explained.The Jones matrix analysis method was used to construct the orthogonal suppression ratio model of the backscattered noise of the circularly polarized light transmission resonator and the RFOG error model caused by the optical Kerr effect.The noise suppression mechanism of the circularly polarized light was clarified,and relationship between the parameters of the resonator and the intracavity coherence were obtained.as the theoretical basis to optimize the resonator design method to improve the noise suppression performance of the resonator.We use this as a theoretical basis to optimize the resonator design method to improve the noise suppression performance of the resonator.Research shows that the designed circularly polarized light transmission resonator can achieve comprehensive suppression of the main non-reciprocal optical noise of RFOG without resorting to external noise suppression means.Aiming at the problem that the closed-loop signal detection method of circularly polarized light RFOG lacks theoretical demonstration and experimental research,the research on the closed-loop detection method of RFOG based on Faraday frequency shifter is carried out.Based on the analysis of the reciprocity of the RFOG system structure,a method of using the non-reciprocal frequency shift characteristics of the Faraday frequency shifter to achieve clockwise and counterclockwise bidirectional frequency shifting of the optical path is designed to solve the problems of non-reciprocity of the optical path structure caused by the independent loop frequency shifting devices.By analyzing the principle of phase equivalence of Sagnac effect and Faraday effect,the Faraday frequency shifter parameters under power constraints are designed to meet the frequency shift requirements of the system.Furthermore,a closed-loop control strategy of Faraday frequency shifter based on interval threshold trigger mechanism is designed to solve the problem of controller noise introduced in the system in real time.Finally,through the modeling and simulation of the closed-loop detection system,the stability of the system is analyzed,and the control parameters are optimized.Research shows that the designed closed-loop detection method improves the structural reciprocity of the RFOG system and effectively reduces the control signal noise.Finally,the designed circular polarization-maintaining fiber resonator was experimentally studied for the optical noise in the cavity,and the resonator was applied to the closed-loop RFOG detection system based on Faraday frequency shifter for performance verification.The experimental results show that the resonance curve of the resonator has obvious single polarization state excitation characteristics,and the light waves propagating in opposite directions have good reciprocity.The resonator can reduce the backscattered noise intensity by 19 d B without resorting to external noise suppression measures,and reduce the RFOG error caused by the Kerr effect by 96%.Comparative tests of different closed-loop RFOG systems using the same circularly polarized light transmission resonator show that the designed closed-loop detection method achieves a bias stability of3.02°/h,which is better than others method.