High-Bandwidth Tracking Method of Resonant Frequency for Sensing Resonators

A novel high-bandwidth tracking system with double closed-loop control is proposed to track the low and high-frequency components of the resonant frequency of sensing resonators. To overcome the low intrinsic bandwidth of lasers, the low-frequency and large range change of the resonant frequency is tracked by adjusting the frequency of the laser. Simultaneously, the rapid and small range fluctuation of the resonant frequency is tracked in real time using an optical single-sideband (OSSB) modulator. The closed-loop error model of resonant frequency tracking is then analyzed and separated into low-frequency and high-frequency signals in the dual tracking system. To achieve high-bandwidth tracking of the resonant frequency, the controllers of the low-frequency and high-frequency control loops are designed to adjust the frequency of the laser and the frequency-shift of the OSSB modulator, respectively. The experimental results indicate that the dual tracking system of the resonant frequency for the sensing resonator has a fast rise time of less than 12 μs and a wide bandwidth of up to 100 kHz, which validate the high dynamic performance of our proposed method.