Progress in Spectroscopy and Sensing Applications of Optical Microcombs

Abstract Optical frequency combs, characterized by their evenly spaced spectral lines with high phase coherence, possess revolutionary measurement capabilities. It is enabling applications in a wide bound of sensing fields, including precision spectroscopy, range measurement, and acoustic sensing. Leveraging parametric frequency conversion, an optical frequency comb can be generated in a microresonator. This approach provides access to high repetition rates at the level of the gigahertz (GHz) or even terahertz (THz), promising ultrafast sensing through chip-scale integration. Its unique spectral feature extends its application areas, such as astronomy, microwave photonics, or molecular fingerprinting. Recent advances have uncovered the general principle of microresonator-based optical frequency combs, helping researchers to generate and control them. Various soliton phenomena in microresonators, including the Stokes solitons, counter-propagating solitons, and soliton crystals, have been reported with the potential to boost the performance of optical frequency combs and ignite design innovation. We review progress in spectroscopy and sensing applications of optical microcombs and discuss current opportunities and challenges.