Rearch On Optical Kerr-Effect In Resonant Micro Optic Gyro

Resonant micro optical gyro (RMOG) is a new-type high-precision inertial angular rotation sensor, which is widely used in navigation and inertial guidance system and has obvious advantages in the aspects of miniaturization and integration. As one kind of the three main optical error sources in the RMOG, the optical Kerr-effect noise comes mainly from the input-intensity mismatch between the clockwise (CW) and counterclockwise (CCW) lightwaves input to the resonator. This input-intensity mismatch will bring about a nonzero bias which is proportional to the input-intensity mismatch to the output of the RMOG, and fluctuations in input intensities will bring about the bias fluctuation and affect the gyro-bias stability. In this article, a high-precision power feedback technique is designed and implemented based on the second harmonic demodulation technique, and the input-intensity mismatch between the CW and CCW lightwaves and their intensity fluctuations both can be reduced greatly through this power feedback technique. The main achievements of this article are as follows:(1) Use the acoustic optic frequency shifter (AOFS) as the power controller to make squared modulation on the lightwave input to the resonator, and the optical Kerr-effect noise of the RMOG is measured by this way. From the test results, we can obtain that the gyro bias error induced by an input-intensity mismatch of1mW is10.7°/s。(2) The relationship between the second harmonic demodulated output and the light-intensity input to the resonator is verified, and the second harmonic demodulated output is used as a way to test the input-intensity input to the resonator, which will improve the detection precision greatly. The second harmonic demodulated circuit is designed and implemented based on a single field-programmable gate array (FPGA), and the performance of the second harmonic demodulated circuit is tested. The equivalent input noise of this circuit is as low as53.9nV/√Hz, and the delay time is smaller than1μs. So this circuit allows RMOG to detect a rotation rate of0.001°/s.(3) On the basis of the second harmonic demodulation technique, two optical power feedback loops are designed and implemented, and one takes the AOFS as the power controller and the other takes the intensity modulator (IM) as the power controller. This two power feedback loops are applied to the practical RMOG system. The gyro bias stability induced by the optical Kerr-effect noise is reduced to1.92X10-5°/s from0.062°/s through the AOFS power feedback loop, and the gyro bias stability induced by the optical Kerr-effect noise is reduced to1.72－10-5°/s from0.03°/s through the IM power feedback loop.Above all, these two optical power feedback ways both can reduce the optical Kerr effect to below the ultimate sensitivity of RMOG, no matter the power controller is the AOFS or IM.