Overview: Resonator fiber-optic gyro (RFOG) is a high-accuracy inertial rotation sensor based on the Sagnac effect, which can achieve tactical applications by using tens of meters or even a few meters of optical fibers. RFOG has attracted much attention for broad application prospects in high precision, miniaturization, and ultra-stability, and it could enable a new generation of optical inertial sensors. The central frequency of the laser to track the resonance frequency of the fiber ring resonator (FRR) is indispensable for a high-performance RFOG. However, the drift of the resonance frequency arising from FRR temperature fluctuation must be eliminated to maintain tracking accuracy, which is achieved by resonant frequency servo loop. In order to improve the frequency servo loop, PI controller, double integral term combined with traditional PI controllers, a multilevel laser frequency lock-in technique is proposed to improve the tracking accuracy. Several frequency locking schemes, based on the acousto-optic frequency shifter (AOFS) and piezoelectric (PZT) cylinder, are proposed to solve the frequency lock-in problems in RFOG. The studies mentioned above are aimed at the tracking accuracy. Actually, the tracking range is also important for RFOG. For example, resonance frequency of the FRR is greatly affected by ambient temperature. Typical temperature coefficient of FRR is up to ~GHz/℃. However, the temperature tuning response of the laser is too slow to satisfy the rapid change of the resonance frequency. For this reason, the PZT is used to realize the fast frequency tuning because of the high bandwidth, which can meet the need of fast frequency tuning. The laser temperature tuning ratio can up to ~GHz/℃ to satisfy the requirement of high bandwidth.

Aiming at the application requirement of resonator RFOG, a frequency tracking and locking control scheme based on laser temperature and PZT control is proposed in this paper. By taking advantages of the large range of laser temperature tuning as well as the high precision and high dynamicity of PZT tuning, the resonator frequency of the resonator cavity is realized by the central frequency of the fiber laser. Transmission resonator signal is simulated by mathematical methods. Hardware design and algorithm simulations of temperature and PZT control scheme are carried out. The influence of control parameters on locking stability in frequency tracking is analyzed. The development of laser frequency locking systems is assembled. The high-precision and long-time tracking of laser central frequency to resonator frequency of resonator cavity is realized, successful. The locking precision of frequency tracking is as low as 4.8×10^-9 over one hour under normal temperature. The locking precision of frequency tracking is as low as 9.74×10^-8 over 5.5 hours under variable temperature. The above research work has laid an important foundation for improving the long-term performance of resonator fiber optic gyroscopes.