Double Closed-Loop Detection Technique And Polarization-Fluctuation Noise In Resonant Micro-Optic Gyroscope

The resonant micro-optic gyroscope(RMOG)based on Sagnac effect is an important approach to realize miniaturization and integration of high-precision gyroscope.It has wide range of applications in micro-satellite attitude control,mini unmanned aerial vehicle and so on.The long-term stability and miniaturization have not yet been solved for the past 30 years,which are mainly due to the temperature-related polarization-fluctuation noise and the compact signal processing technique with high-accuracy.The double closed-loop detection can improve the linearity and dynamic range of the RMOG output.The key issue is the adoption an integrated optical phase modulator to realize equivalent frequency shift based on a single field-programmable gate array(FPGA)for the RMOG with a centimeter-scale waveguide-type ring resonator(WRR).Therefore,the double closed-loop detection scheme and the polarization-fluctuation induced drift in the RMOG are studied in the dissertation.The major innovative achievements are summarized as follows.(1)The double closed-loop detection technique used in the RMOG is innovatively proposed in the dissertation.A combination modulation scheme of the sinusoidal wave and a stair-like digital serrodyne wave on single phase modulator is proposed to achieve the double closed-loop RMOG.In this scheme,the sinusoidal wave is mainly used for gyro signal modulation and demodulation.The serrodyne wave purely acts as a frequency shifter for the second closed-loop.Both the theoretical and experimental investigations are presented in the dissertation.The theoretical investigations show that the width of one stair of the stair-like digital serrodyne is not limited by the optical transmission time of the waveguide-type ring resonator(WRR).In condition of the rise time of the digital-to-analogue converter(DAC),the maximum sideband suppression can be attained when the amplitude of the digital serrodyne wave is set to be ? and the width of one stair is equal to the rise time of the DAC,hence the gyro detection error is minimum.Experimentally,the performance of the output of the lock-in amplifier is measured based on the double closed-loop RMOG.The precision of the two closed-loop are 0.1°/h and 0.2°/h,respectively,which illustrates the effectiveness of the proposed scheme.The dynamic range and the linearity of the single and the double closed-loop RMOGs are also measured,respectively.With the dynamic range of ±5000°/s.the linearitv of the double closed-loop RMOG is high as 99.994%.corresponding to the 99.892%of the single closed-loop scheme.(2)The theory and experimental investigations on the influence of the polarization characteristics of the WRR to the detection accuracy of the RMOG.The polarization analysis model of the WRR is established based on Jones transfer matrix method.The polarization characteristics of the reflection-type WRR are obtained.The analysis results show that the method of the polarization extinction ratio(PER)increasement in-cavity has more advantage than the method of the out-cavity.The abnormal phenomenon of the resonance peak should be avoided in the practical operation.The single-polarization fiber(SPF)pigtailed WRR and the integration technique of 45° tilted gratings in-cavity are proposed in the dissertation to suppress the polarization-fluctuation noise.Compared with the PMF-pigtailed WRR,the PER of the SPF-pigtailed WRR is improved from 10.69 dB to 18.9 dB.The PER of the WRR with the integration of 45°tilted gratings in-cavity is more than 26.5 dB,which also has good temperature characteristic.Experimentally,the polarization noise is measured as 2.14(°/s/)? using the SPF-pigtailed reflection-type WRR,which is consistent with the simulation result of 1.8(°/s/)?.In order to calculate the polarization-fluctuation noise because of the nonreciprocity of the two directions(clockwise and counter clockwise)of the WRR,an optimized calculation model is established.Four parameter differences are considered for simulation:the PER difference of the input light,the aligned angle difference between the fiber and the waveguide,the polarization aligned angle difference of the coupler of the WRR and the polarization correlation characteristics of the coupler of the WRR.The polarization-fluctuation noise of the though port and the add port of the transmission-type WRR are simulated and measured.The results show that the polarization-fluctuation noise of the add port is less than the through port.Based on the aforementioned work,the SPF-pigtailed WRR with a length of 7.9 cm and a diameter of 2.5 cm is fabricated based on the silica waveguide.The finesse and the resonant depth of the WRR are 196.7 and 98%,respectively.The finesse is the highest value of the silica WRR reported in the open literature.Experimentally,the performance of the double-closed RMOG using the SPF-pigtailed silica WRR is measured.The bias stability of the RMOG is 0.004°/s over a one-hour timeframe.The sinusoidal swing measurement shows that the RMOG based on silicon substrate capable of detecting the earth rotation has been achieved for the first time.