Photonic chip-based optical frequency division with PZT-integrated soliton microcombs

Optical frequency division (OFD) produces low-noise microwave and millimeter-wave (mmWave) signals by transferring the exceptional stability of optical references to electronic frequency domains. Recent developments in integrated optical references and soliton microcombs have paved the way for miniaturizing OFD oscillators to chip scale. Critical to this realization is a rapid tunable frequency comb that is stabilized to the optical references, thereby coherently linking optical and electronic frequencies. In this work, we advance the on-chip OFD technology using an integrated high-speed lead zirconate titanate (PZT) stress-optic actuator on the SiN soliton microcomb resonator. The integrated PZT actuator tunes the resonance frequency of the soliton-generating microresonator with a bandwidth exceeding 10s MHz and thus adjusts the soliton repetition rate. Optical frequency division and low-noise mmWave generation are demonstrated by feedback control of the soliton repetition rate through the integrated PZT-actuator, and the soliton microcomb is stabilized to a pair of reference lasers that are locked to an integrated 4 m SiN coil reference cavity. Our approach provides a fast, versatile, and integrated control mechanism for OFD oscillators and their applications in advanced communications, sensing, and precise timing.