Extended Data Fig. 4: On-chip generation of PDH error signals using the HBAR modes induced by AlN actuation.
From: Monolithic piezoelectric control of soliton microcombs

a, Experimental set-up. LPF, low-pass filter; Amp., RF power amplifier. b, The measured S21(ω) response of the AlN actuator on a linear frequency scale. Measurements are taken when the laser is on-resonance and off-resonance. c, PDH error signals modulated at the four HBAR frequencies marked with stars in b.