Optical Path Optimization And Noise Suppression Of Resonant Fiber Optic Gyroscope

Gyro is an inertial sensor for the rotation rate measurement.Resonant fiber optic gyro(RFOG)based on the Sagnac effect has the advantages of high sensitivity and large dynamic range.When compared with the traditional interferometric fiber optic gyro(IFOG),RFOG can achieve the same detection precision as IFOG with a much shorter fiber length,which gives evident superiority in the further integration,as well as improves its application value in the fields of navigation,aerospace,defense industries,and guidance systems.This thesis conducts in-depth and meticulous research on RFOG optical path optimization and optical noise suppression.Related research work can be summarized as follows:(1)Based on the multi-beam interference mechanism,the transmission process of light wave in the fiber ring resonator(FRR)is deduced.The transmission model of light wave in FRR is simulated.The influence of the parameters(including the line width of the laser,the length of the cavity,the split ratio of the coupler,the additional loss of the coupler,the loss of the fiber,etc.)on the main performance parameters(including fineness and resonant depth of the resonant curve)of the FRR is analyzed,which provides theoretical guidance and reference for experimental research.(2)Through the theoretical simulation method,the influence of the coupler normal mode loss difference(the phase difference between the coupler cross port output optical field and direct port is less than the ideal ?/2)on the symmetry of resonant curve,the resonant signal modulated by the triangular wave,and the demodulation curve are analyzed.Moreover,the asymmetry of the resonant curve leads to the asymmetry of the resonant signal modulated by the triangular wave and the demodulation curve from the theoretical simulation and the experiment.Two schemes for solving the asymmetry of the resonant curve caused by the coupler normal mode loss difference are proposed.(3)The sources and effects of stimulated Brillouin scattering and Rayleigh backscattering in RFOG are analyzed.The backscattering noise test system is built to observe and analyze the characteristics of the backscattering curve.The threshold value of stimulated Brillouin scattering is 7.278 mW.Thus,the input optical power of the FRR is controlled below the threshold value.Thereby the suppression of stimulated Brillouin scattering is achieved.Theoretically,the principle of the self-heterodyne optical path is derived,and then the selfheterodyne optical path test system is built.Finally,the maximum optical carrier rejection ratio is 61.734 dB when using triangular wave modulation,and the maximum optical carrier rejection ratio is 50.87 dB when using sine wave modulation.After measuring the best voltage amplitude of the modulation signal,then optimizing the voltage applied to the phase modulator,and finally suppressing the Rayleigh backscatter noise.(4)The source and influence of polarization noise in the RFOG are analyzed.Based on the transfer matrix method,it is inferred that the single-point 90° fusion FRR,the double-point 90° fusion FRR,and the polarization-preserving photonic crystal fiber(PM-PCF)hybrid resonator can effectively suppress the polarization noise.An optical path structure capable of simultaneously detecting the polarization characteristics of two resonant rings is proposed.Experimental comparisons are made among the four schemes.Compared with the 0° fusion FRR,the temperature stability of the double-point 90° fusion FRR is increased by 71.242 times,which means that the polarization noise is effectively suppressed.When a single-point 90° fusion FRR is used,the single-pass phase change difference between the two polarization states is substantially stabilized in the vicinity of ?,and the one-way phase change difference between the two polarization states is substantially not fluctuated according to the change of the ambient temperature.The temperature stability of the PM-PCF hybrid resonator is 3.2478 times that of Panda-PMF resonator,which proves that the temperature stability of PM-PCF is better than Panda-PMF.With the improvement of the drawing process and fusion technology of PCF,the PCF-RFOG will be a new type of RFOG with potential technical advantages such as miniaturization and high precision.Based on the above work,the optical path of RFOG was optimized,and the gyro prototype was finally built.The scale factor is 9.17064/(°/h).In the case of the integration time of 100 seconds,the zero-bias stability of the gyro prototype is 9.5°/h within 1 hour.