  Laser based ranging (LiDAR) - already ubiquitously used in industrial
monitoring, atmospheric dynamics, or geodesy - is key sensor technology.
Coherent laser ranging, in contrast to time-of-flight approaches, is immune to
ambient light, operates continuous wave allowing higher average powers, and
yields simultaneous velocity and distance information. State-of-the-art
coherent single laser-detector architectures reach hundreds of kilopixel per
second rates. While emerging applications such as autonomous driving, robotics,
and augmented reality mandate megapixel per second point sampling to support
real-time video-rate imaging. Yet, such rates of coherent LiDAR have not been
demonstrated. Here we report a swept dual-soliton microcomb technique enabling
coherent ranging and velocimetry at megapixel per second line scan measurement
rates with up to 64 spectrally dispersed optical channels. It is based on
recent advances in photonic chip-based microcombs that offer a solution to
reduce complexity both on the transmitter and receiver sides.
Multi-heterodyning two synchronously frequency-modulated microcombs yields
distance and velocity information of all individual ranging channels on a
single receiver alleviating the need for individual separation, detection, and
digitization. The reported LiDAR implementation is hardware-efficient,
compatible with photonic integration, and demonstrates the significant
advantages of acquisition speed afforded by the convergence of optical
telecommunication and metrology technologies. We anticipate our research will
motivate further investigation of frequency swept microresonator dual-comb
approach in the neighboring fields of linear and nonlinear spectroscopy,
optical coherence tomography.
