Scale Factor Nonlinearity of Closed-loop R-FOG Based on Square-wave Modulation

The closed-loop control scheme of the resonator fiber optic gyro(R-FOG) based on square-wave frequency modulation is proposed.When the optical frequency drifts from the resonant center frequency,the reflection intensity of R-FOG becomes a square-wave intensity-modulated signal,from which the R-FOG can be closed-loop operated when the optical frequencies of clockwise(CW) and counter-clockwise(CCW) light beams are locked on the resonant frequencies.The closed-loop frequency locking is realized by adjusting the optical frequency of the laser and modulating the frequency offset,and the locking precision is decided by the precision of control system.The scale factor nonlinearity of a closed-loop R-FOG based on square-wave frequency modulation is analyzed.It is found that the nonlinearity depends on the precision of frequency control and the resonator fineness.For a resonator with 50 fineness,the nonlinearity of a hundred per million for scale factor requires the precision of frequency control better than 1113Hz,and for a resonator with 100 fineness,the precision of frequency control better than 605 Hz is required.