Improving thermal stability of a resonant fiber optical gyroscope using triple closed loops

A closed-loop resonant fiber optic gyroscope (RFOG) configuration with three resonance frequency servo loops is proposed. By using one laser-servo loop and two symmetrical phase modulator (PM) servo loops, the effect of the reset due to the limited tracking range of the laser-servo loop is solved. Further long-term stability for 48 h and thermal stability at moderate rate measurements show that the output of the triple closed-loop RFOG is insensitive to environmental temperature variations. When the temperature increased from 17.5°C to 40.7°C in 1800 s and the maximum temperature rate was about 0.025°C/s during heating, the laser-servo loop was reset a total of 413 times. However, the output of the triple closed-loop RFOG is not affected by those frequent resets in the laser-servo loop because the two PM-servo loops are free of glitch pulses under this new scheme. Compared to the traditional double closed-loop RFOG, the thermal bias stability of the triple closed-loop RFOG is improved by a factor of 15 times from 29.8°/h to 1.88°/h.