An open-loop RFOG based on 2nd/4th harmonic feedback technique to suppress phase modulation index's drift

In this paper, how the phase modulation index's drift affects an open-loop resonator fiber optic gyro's (RFOG's) performance is discussed. By using the ratio of the second to fourth harmonic (2nd/4th harmonic), a harmonic feedback technique is proposed to suppress this drift. It is found that the phase modulation index's drift would lead to a significant measurement error, which increases with rotation rate. It is proven that there exists an approximately linear correlation between phase modulation index and 2nd/4th harmonic. Using this correlation, the 2nd/4th harmonic feedback technique is applied to the open-loop RFOG to stabilize the phase modulation index. Although the phase modulation index slightly deviates from its optimal value in the dynamic state with this technique, it is proven that the induced backscatter noise could be neglected. The test results indicate that the phase modulation index's drift with this technique is reduced to about 22% of that without suppression technique, and the stabilities of gyro output signal are respectively improved by about 29% and 31% under 5deg/s and 10deg/s when this technique is used. It is concluded that the 2nd/4th harmonic feedback technique does work in suppressing the phase modulation index's drift.