Signal Detection Technique Of Resonant Fiber Optic Gyro

Resonant fiber optic gyro(RFOG)is a high accuracy rotation rate sensor based on Sagnac effect,whose key sensing element is the fiber ring resonator(FRR).Compared with the traditional interference fiber optic gyro(IFOG),the RFOG can achieve the same precision with shorter fiber length,which has advantage in system miniaturization.Phase modulation and demodulation,and resonant frequency servo loop are two main techniques in RFOG signal detection.Based on the field programmable gate array(FPGA),this dissertation focuses on the optimization designs and performance tests of the two modules,and applies them to the practical RFOG system.The main researches including:(1)Develop the digital sinusoidal modulation and synchronous square wave demodulation technique and verify the advancement of square wave demodulation.The digital sinusoidal wave is generated by CORDIC algorithm,and the synchronous square wave demodulation is realized by the digital switch,which reduces the source occupation of the FPGA and decreases the signal processing delay.The equivalent input noise of the square wave demodulation module is 9.33nV/?Hz.Compared with the RFOG applied with the sinusoidal demodulation,the RFOG applied with the synchronous square wave demodulation technique increases the slope of the demodulation curve by a factor of 1.56 and improves the RFOG short term bias stability by a factor of 1.47.(2)Develop the resonant frequency servo loop consisted of the laser feedback loop and the phase modulator(PM)loop.Based on the loop transfer function,the analysis module of the resonant frequency servo loop is established and the loop parameters,including the low-pass filter(LPF)time constants,the loop gains and the delays of the two loops,and the integration time of the proportional-integral controller,are analyzed and optimized.The theoretical analysis result proves that the optimized resonant frequency servo loop has shorter loop delay and wider loop bandwidth.The laser low frequency noise is suppressed by the laser feedback loop and the PM feedback loop provides laser high frequency noise suppression and reduces the influence of the laser frequency noise at the even harmonics of the modulation frequency on the RFOG precision.The low delay characteristic of the PM feedback loop can realize the fast track and lock of the laser center frequency and improve the temperature stability of the RFOG.(3)Establish the RFOG system with implementation of the optimized resonant frequency servo loop including the laser feedback loop and the PM feedback loop.The simulation of the laser frequency noise by sinusoidal phase modulation and the fast temperature variation test verify the high frequency noise suppression ability and the quick response characteristic of the PM feedback loop,respectively.The test results prove that the PM feedback loop suppresses the intermodulation noise resulted from the white noise at the second harmonic and the fourth harmonic of the modulation frequency by 12.68dB and 1.51dB,respectively.When the temperature varies by 12? during 6 minutes,the bias stability of the RFOG increases from 41.93°/h to 36.65°/h.With the application of the optimized demodulation module and the resonant frequency servo loop module to the RFOG,the best Allan deviation of the RFOG bias stability is approximately 3°/h under laboratory environment.