Double Closed-loop Resonator Integrated Optic Gyroscope

Gyroscope plays an important role in the field of navigation and guidance. Optical gyros based on the Sagnac effect are the perfect candidates for the inertial navigation system. Compared with the micro-electromechanical system (MEMS) gyro, the R-IOG with no moving parts is insusceptible to instantaneous shock and vibration. Compared with the interferometer fiber optic gyro (I-FOG) or the He-Ne ring laser gyro (RLG) with discrete components, the resonator integrated optical gyroscope (R-IOG) shows advantages in miniaturization and integration.Waveguide ring resonator (WRR) is a sensing element of the R-IOG. In order to improve the long-term stability of the R-IOG, the polarization characteristic of the WRR is deeply studied, so as to reduce the gyro drift caused by the polarization fluctuation noise. In order to enhance the gyro bandwidth, the double-closed signal detection technique based on the R-IOG is designed in depth. The main innovational work and achievements are concluded as follows:A mathematical model of the polarization characteristics of the WRR is established based on the transfer matrix method. The influences of the polarization fluctuation noise on the R-IOG at different temperatures are studied for the first time. The influence of the structure features of the WRR, the states of the input lightwave and the birefringence of the waveguide on the deviation of the resonance frequency of the primary eigenstate of polarization (P-ESOP) can be fully calculated based on the mathematical model. The gyro drifts at different temperatures differ greatly according to the influence mechanism of the polarization noise in the R-IOG. The resonance dips of the two ESOPs coincide at the temperature of 25℃. The bias stability is 0.67°/s at the temperature of 16.23℃,which is about 20 times smaller that at the temperature of 24.28℃with the bias stability of 13.6°/s. The countermeasures to the polarization fluctuation noise of the R-IOG are included as follows:increasing the polarization extinction ratio of the resonator and the input lightwave, decreasing the polarization dependent loss at the coupler, using the polarization independent elements at the resonator output, balancing the powers of the CCW and CW lightwaves, applying the proper WRR temperature and improving the accuracy of temperature controller. Besides, polarization fluctuation noise also influences the resonance lineshape of the WRR. leading to the asymmetry of the resonance curve. When the phase modulation spectroscopy technique (PMST) is applied in R-IOG, the offset errors of the gyro are affected not only by the resonance asymmetry in the WRR but also by the modulation parameters in the PMST. The resonance curves of the WRR at different temperatures are measured and different resonance asymmetry ratios (RAR) appear. The relationship between the offset errors and the modulation frequency difference on the condition of different RARs are measured as well. Offset errors and bias stability of the R-IOG can be greatly reduced by the set of a proper temperature to reduce RAR and the selection of the proper modulation frequencies in the CW and CCW lightwaves.The closed-loop signal detection technique is deeply analyzed. The reduction of reciprocity noises and the enhancement of gyro bandwidth conflict with each other in the single closed-loop R-IOG. The simulation model is firstly set up for the analysis of the characteristics of the single closed-loop and three typical double closed-loop R-IOG schemes. The differential double closed-loop signal detection scheme is the ideal choice for the R-IOG in the aspects of both the reciprocity noises reduction and the gyro bandwidth enhancement.Based on the work mentioned above, an all-digitalized experimental system of the differential double closed-loop R-IOG is set up. In the R-IOG, a polarization-maintaining WRR with the length of 79 mm is temperature controlled. In the rotation range of±1000°/s, the linearity of the double closed-loop R-IOG is 99.995% which is better than that of the single closed-loop system (99.969%). The theoretical bandwidth of the gyro is 25 rad/s. The bias stability of the R-IOG is 0.53°/s(1σ)for an hour. To our knowledge, it is the best long time bias stability of the double closed-loop R-IOG.