Modulation index detection and stabilization technique of phase modulator in resonant fiber optic gyro base on sampling demodulation

A new modulation index detection and stabilization technique (MIDST) based on sampling demodulation is proposed to reduce the influence of phase modulator (PM) thermal instability on resonant fiber optic gyro (RFOG). Firstly, the factors causing the PM thermal instability and the influence on RFOG are analyzed. Then, a phase modulation index detection technique is proposed to detect the fluctuation of modulation index without complicating the optical path configuration of RFOG. Finally, considering the temperature fluctuation, a modulation index stabilization loop based on auto disturbance rejection controller (ADRC) is designed to stabilize the phase modulation index. In experiments, modulation index can be detected in real time and accurately, and the fluctuation is reduced from 10% to 0.3% over 100 °C temperature range (−40 °C to ＋60 °C) with MIDST. The stability of scale factor and the suppression effect of backscattering noise could be improved effectively. •Theoretically analyze the factors affecting the thermal stability of PM’s modulation index.•A novel modulation index detection and stabilization technique (MIDST) of PM in ROG based on sampling demodulation is proposed.•The fluctuation amplitude of the PM’s modulation index is reduced from 10% to less than 0.3% over 100 °C temperature range (−40 °C to ＋60 °C) with MIDST.