Analysis and suppression of square wave modulation errors in FOG

Based on the principle of square wave modulation and demodulation in fiber optic gyroscope (FOG), the effects of the square wave frequency, phase and duty cycle and the fiber coil eigenfrequency upon square wave modulation errors were discussed. The temperature coefficients of the fiber coil eigenfrequency and square wave frequency, duty cycle and phase were measured by using a lock-in amplifier. The bias drift of FOG due to the square wave modulation errors was analyzed at different temperatures. A digital time-domain comb filter was presented and a conditional expression was derived to eliminate the square wave modulation errors steadily. The test results show that the bias drift, brought by square wave modulation errors, is reduced to less than 0.3°/h by applying digital time-domain comb filter in FOG.