Modulation spectrum analysis and optimization for closed-loop RFOG under dynamic condition

In this paper, the spectrum characteristics of the closed-loop RFOG, modulated by the digital sine and bipolar serrodyne wave, is analyzed under the dynamic condition. It is verified that the serious spectrum overlapping between the CCW and CW loops would be induced within a certain rotation rate range, which would increase the backscatter noise. Experimental tests indicate that the serious spectrum overlapping could more than double the standard deviation of gyro output signal, which badly deteriorates the gyro's performance. According to the spectrum characteristics analysis result, to reduce the spectrum overlapping induced backscatter noise under the dynamic condition, a noise suppressing algorithm is proposed. This algorithm is realized by switching the initial reset frequency of the bipolar serrodyne wave at a crucial rotation rate to keep an enough frequency difference between the two modulation spectrums' main harmonic components. Experimental test shows that when this algorithm is used, the decreased ratio of the standard deviation for gyro output signal can reach to about 70.5% at the rotation rates corresponding to the serious spectrum overlapping.