Research On BFOG And Brillouin Fiber Ring Resonator

Fiber optic gyro (FOG) is an inertial angular velocity sensor based on the Sagnac effect, which plays an important role in a variety of navigation and guidance system. At present, the interferential fiber-optic gyro (IFOG) has reached a mature state, but it faces some difficulties such as miniaturization. Compared with IFOG, Brillouin fiber optic gyro (BFOG) has great predominance in fiber length and signal processing system. Therefore, the research on BFOG is of great significance. Brillouin fiber ring resonator (BFRR) is the core and main part in BFOG, and it is also the linchpin to achieve BFOG. So a number of key issues in BFRR were studied in this dissertation, detailed as follows:First of all, the optical intensity in BFRR was studied in detail. The easy-to-digest method was taken on optical analysis, in order to analyze the basic characteristics of passive cavity before BFRR. And then the Taylor series was used to simplify the description of characteristics of cavity. Combined with recursive thinking, the relationship among incident light, circuiting light, different order Stokes light and transmitted light were derived. Considering BFOG requirements, the incident light should be controlled in the first window, and the cavity must be over-coupled. At last, the BFRR was designed, in which the FSR is 19.35MHz and the finesse is 70. In our experiments, theory of pump threshold and Stokes optical power was testified, and the over-tear welding method was utilized to design the cavity which suitable for BFOG.In the experiments, the resonance peaks shift and vibration was discovered, so the dynamic performance of BFRR were researched in the dissertation. First the impact of polarization fluctuations that arises from optical birefringence on stimulated Brillouin scattering and cavity effects were studied, and the technique of achieving a stable resonant cavity were analysed. Theoretic analysis showed that, the root causes of resonance peaks vibration came from too fast PZT modulation rate, and then its impact on gyroscope were studied. Analysis showed it is difficult to maintain stable cavity length in actual environment, so the DC frequency stabilization method based on PID control was derived, and FPGA-based frequency stabilization circuit was designed. Results showed that the resonant frequency stability was controlled under 9.45Hz. Then, the research of BFOG modeling and other related theory were carried out to improve BFOG theoretical system. The Jones optics was adopted to establish the optical transmission model of BFOG. According to this model, the optical output under ideal and non-ideal condition was discussed. Results showed that the light source power fluctuations and polarization fluctuations played an important role in the gyro sensitivity, and the parameters of coupler and polarizer also had appreciable effect. How to choose the optical source power and fiber ring length was discussed afterwards, and the conclusion showed that, the peak output optical source power should be larger than 4mW, the power fluctuations should be less than 10μW, the frequency fluctuations should be less than 10KHz, and the best fiber length is 10m. Aimed at the conflict between the threshold power and BFOG dynamic range, the "two-way winding" method was brought forward, which enhanced the gyro dynamic range under the premise of optical power threshold. At last, the BFOG frequency read out system was designed on reference of RLG.Finally, research of Kerr effect in BFOG was carried out. Kerr effect was recognized as the main error sources in BFOG, so the research of this part is of great significance. Through basic analysis of fiber-optic nonlinear optics, the cross-phase modulation had been shown to be the main reason of refractive index change. Though theoretic analysis, Kerr effect may produce optical bistablity. Experiment showed it happened as the input power was 440μW, and the bistablity could be restrained by adjusting the coupling parameters. The main reason for Kerr effect in BFOG was resonant detuning. It brought not only the nonlinear output, but also restricted-the gyro dynamic range. The double-loop BFOG program was proposed for this suit, and the adverse effects of gyro output was avoided theoretically. Then the parameter error of double-loop scheme was discussed, and results showed that total additional frequency was less than 10Hz, which means its impact on gyro zero-drift was less than 0.015°/s. The results could meet moderate FOG requirements.