Zero-deviation effect in a resonator optic gyro caused by nonideal digital ramp phase modulation

Resonator fiber optic gyro (RFOG) is a high accuracy inertial rotation sensor based on the Sagnac effect. The digital ramp phase modulation technique is usually adopted instead of analog modulation to improve accuracy and stability. Failure to keep the stair-period of the digital ramp waveform equal to the optical transmission time in the fiber ring resonator produces errors in the RFOG. The influence of the nonideal stair period on gyro performance is firstly fully developed in this paper. The physical mechanism is an uncertain phase relationship between the transmitted light and the circulated light components in the resonator occurring in this nonideal stair-period. The effect on output signals of the resonator is fully analyzed. Through simulation, it is found that the zero position of the demodulation curve in the symmetrically digital triangle phase modulation technique is not affected by the nonideal stair-period problem. However, in the two-frequency combined digital serrodyne phase modulation technique, much effort is needed to overcome the zero-deviation, which causes errors in the RFOG.