Fig. 1: Concept of 2P-OFD for low-noise microwave generation.
a, Two semiconductor lasers are injection locked to chip-based spiral resonators. The optical modes of the spiral resonators are aligned, using temperature control, to the modes of the high-finesse F-P cavity for PDH locking. b, A microcomb is generated in a coupled dual-ring resonator and is heterodyned with the two stabilized lasers. The beat notes are mixed to produce an intermediate frequency, fIF, that is phase-locked by feedback to the current supply of the microcomb seed laser. c, An MUTC photodetector chip is used to convert the microcomb’s optical output to a 20 GHz microwave signal.
