A closed-loop RFOG based on digital serrodyne and sine modulations with two LiNbO3 phase modulators

Abstract

Based on the digital bipolar serrodyne and sine phase modulations, a closed-loop RFOG with two LiNbO3 phase modulators is proposed and studied. Through theoretical simulation, the bipolar serrodyne waveform is optimized to improve the detection sensitivity. By the characteristic analysis of the practical serrodyne phase modulation spectrum, the sine modulation frequency is optimized to reduce the two loops’ spectrum overlapping, which would lead to the backscatter noise. The optimization result is verified by the gyro output signal tests under the different sine phase modulation frequencies. It is concluded that in order to avoid the spectrum overlapping, the difference between the sine modulation frequency and serrodyne modulation reset frequency should be properly increased, and the sine modulation frequency is required to be close to an even multiple of the serrodyne modulation repetition frequency. Finally, using the optimized phase modulation parameters, the gyro output signal is tested with an integration time of 0.1 s over 1 h, and the bias stability around 7.1 deg/h based on the Allan deviation analysis is obtained.