Chip-scale laser frequency microcombs has achieved equidistant coherent frequency markers over a broad spectrum, advancing frontiers in ultrafast frequency metrology, laser spectroscopy, dense communications, and precision metrology. In this talk we will describe advances in the generation of laser frequency microcombs in dispersion-engineered microresonators with terahertz frequency spacings. We start with the understanding of the phase- and frequency-noise characteristics of a variety of microcomb states, including the generation of THz Turing patterns in optical microcombs. Referenced to external high-purity sources, the microcombs – in the mmWave and THz frequency spacings – can preserve tooth-to-tooth relative frequency stabilization to an uncertainty of 50 mHz and 2.7e−16.
Subsequently, these frequency microcombs drive the chip-scale efficient plasmonic photomixers from the Jarrahi group at UCLA, where together we are able to generate coherent and broadly-tunable THz-mmWave radiation generation. Coherent terahertz radiation spanning 2.8-octaves is achieved from 330 GHz to 2.3 THz, with ~ 20 GHz cavity-mode-limited frequency tuning step and ~ 10 MHz intracavity-mode continuous frequency tuning range at each step. By stabilizing the microresonator pump power and wavelength, we observed sub-100 Hz linewidth of the terahertz radiation with 1e-15 residual frequency instability. The room-temperature coherent frequency-agile THz radiation offers unique capabilities in metrology, sensing, imaging and communications.
|