“…The PDH technique utilizes the lock-in technique that can avoid the influence of light intensity perturbation to generate a higher signal-to-noise ratio (SNR) discriminating signal. Due to the high sensitivity and SNR [2,3,4] of PDH technique, studies on vibration detection [5], strain sensing [5,6,7,8,9], microcavity gyroscope [4,10], particle detection [11,12], and pressure tuning and sensing [13] have been published. Up to now, PDH sensing demodulation is processed by the lock-in technique, and the modulated output is directly mixed with the local oscillation, which also drives the phase modulator.…”