Research On Resonator Micro Optic Gyroscope

Optic gyros with no moving parts based on the Sagnac effect are the perfect candidate for the inertial navigation system. There are two very successful types of optic gyros:He-Ne ring laser gyro (RLG) and interferometric fiber optic gyro (IFOG). With the development over past several decades, these two types of optical gyros show a good measurement performance, although there are some other potential alternatives. However, the conventional RLG and IFOG are not easy to be applied in the areas required for cheap and micro gyros, for the reason that they are complicated in fabrication process with a lot of individual components. With the development of the monolithically integrated optical components on waveguide circuits and batch micro fabrication techniques, R-MOG (Resonator Micro Optic Gyroscope, R-MOG) can solve the difficulty in gyro technology, such as the requirement of light weight and small size, low cost, low power consumption and so on. So, it is meaningful to do research on the key technologies of R-MOG.Sagnac effect of R-MOG is a very weak effect. It is an important research of optical noise suppression and the signal noise ratio (SNR) improvement. This dissertation will do the research on the gyro signal detection and optical noise suppression, and then propose the suitable countermeasures. Finally, the R-MOG system is constructed with these countermeasures. The experimental results are obtained and the countermeasures are verified very usefully. The main innovational work and achievements can be concluded as follows:(1) Based on phase modulation spectroscopy, the DPMT (Double phase modulation technique, DPMT) is proposed. The theory and experimental results indicates that the DPMT can be used to detect the gyro signal. Backscattering error is about～79rad/s in R-MOG if there is no countermeasure. A total carrier suppression of 120 dB is required to reduce this backscattering error to the shot noise limited sensitivity of the R-MOG. For the reason that the carrier suppression of DPMT can easily reach 160 dB, the DPMT can easily reduce the backscatter error to the shot noise limited level. With the same experimental condition, the comparison of backscatter noise suppression in the R-MOG has been done with the DPMT and SPMT respectively. The bias stability of the R-MOG has been improved about two orders of magnitude after using the DPMT. And the experimental results indicate that the backscatter noise is not dominant in the output of the R-MOG with DPMT. The accuracy of the modulation amplitude is relaxed from±1.8 mV to±60 mV with a half-wave voltage of 3 V. When the modulation amplitude is stable, the temperature stability requirement relaxes from±1.6℃to±51℃after applying the DPMT, when the temperature coefficient of the half-wave voltage of the LiNbO3 phase modulator is about 500 ppm/℃. That is to say, more than 30 times relaxation is achieved compared with the SPMT for the backscattering error suppression.(2) The digital PI (Proportional Integration, PI) is adopted in the feedback loop of R-MOG. With the experimental results, Z-N parameter adjusting method and the temperature of the waveguide ring resonator, the optimal parameters of PI are obtained. There are 3-dB break frequency 70Hz and proportional coefficient 2667 respectively. The noise spectral density～5.9Hz/VHz is obtained with the optimal digital PI scheme, which is close to the shot noise limited spectral density 4.OHz/√Hz. The Allan deviationσ(τ) for optimal PI lock is roughly proportional toτ-1/2 up to integration times of 1200s. It indicates that the equivalent output of error Signal is limited by random noise rather than by drifts, when the optimal digital PI lock is implemented. The error signal induced by the optimal PI lock can be negeleted when the R-MOG is with the angular acceleration of less than 1000°/s2。(3) The R-MOG system is constructed with the optimal DPMT optical modulation and optimal digital PI technology. The backscatter error is verified to be reduced to the level less than the shot noise limited of R-MOG with the DPMT. And based on the digital PI feedback scheme, the reciprocal noise is reduced to the level of minimum sensitivity in R-MOG. Finally, the R-MOG output is obtained when the system is at rest. The noise level of 1.85×10-4 rad/s (～38°/h) for 60 seconds duration is obtained. The rotation tests on R-MOG from 0.1。/s to 5。/s are tested, where the processing circuit of R-MOG is implemented by the instruments. The larger rotation test over a range of±550°/s has been successfully obtained with all the processing circuit implemented in FPGA. R2-nonlinearity of this digitalized R-MOG is 0.0169%. To our knowledge, these results are the best results ever demonstrated in silica WRR and the ring length is as short as 7.9 cm.In a word, the R-MOG system is constructed and the experiments are obtained. To our knowledge, the short term stability～38°/h, the rotation of 0.1°/s and the continous rotation test results from -550°/s to +550°/s (R2-nonlinearity 0.0169%) of R-MOG are the best results ever demonstrated in the silica waveguide ring resonator with the ring length as short as 7.9 cm.