Design And Implementation Of Triple Closed-loop Resonant Fiber Optic Gyroscope

Resonant fiber optic gyroscopes(RFOGs)are high-precision angular velocity sensors based on the Sagnac effect.Compared with interferometric fiber optic gyroscopes,RFOGs can achieve the same detection accuracy with shorter sensing fibers,thus have unique advantages in miniaturization.In RFOGs,multiple phase modulators are often used to complete functions such as signal modulation,carrier suppression and frequency shift.The cascade of multiple phase modulators induces several problems.Therefore,a single Y-Branch phase modulating technique is developed.Since the Sagnac effect is a weak non-reciprocity effect,the highly reciprocal optical path structure is very important for effectively detecting the Sagnac frequency difference.Combined with the single Y-Branch phase modulating technique,a triple closed-loop signal detection scheme with full symmetry structure is proposed.With an FPGA as the core signal processing platform,a triple closed-loop RFOG is designed and implemented.Specifically,main works are as follows.(1)A single Y-Branch phase modulating technique is proposed to achieve signal modulation,carrier suppression and frequency shift functions,which avoids the problem of end face reflection caused by the cascade of multiple phase modulators,and is conducive to the miniaturization of RFOG.A self-heterodyne test system is set up to test the function and performance of the single Y-Branch phase modulating technique.The test results show that using this technique,the carrier suppression ratio 1s 58.9 dB,and the sideband suppression ratio of sawtooth frequency shift is 57.6 dB.(2)A triple closed-loop signal deteetion scheme with full symmetry structure is proposed to improve the reciprocity of optical paths.The frequency domain analysis model of the triple closed-loop RFOG is established,and the simulation and parameter optimization of the system is completed.The advantages of the triple closed-loop RFOG on the suppression of reciprocity noise,linearity of the scale factor,dynamic range and temperature stability is analyzed.Especially,the reciprocity structure can effectively eliminate the glitch generated at the output of the gyro in a fast temperature-changing environment.(3)Combining the single Y-Branch phase modulating technique,using an FPGA as the core digital signal processing platform,a triple elosed-loop RFOG is designed and implemented.The resonance curve,demodulation curve,bias stability and temperature characteristics are tested.The test results show that the bias stability is 1.67 deg/h under the test time of 1800 seconds and the bias stability is 6.76 deg/h under the test time of 48 hours.When the temperature of the fiber ring resonator varies from 17.5 ? to 40.7 ? during 1800 seconds and the maximum temperature change rate is 1.5 ?/min,the bias stability of the triple closed-loop RFOG is 2.27 deg/h,which improves by 13 times compared to the result of the double closed-loop RFOG of 29.8 deg/h.