Second-harmonic assisted four-wave mixing in chip-based microresonator frequency comb generation

TL;DR

This paper demonstrates a novel phase-matching method in chip-based microresonators that enables frequency comb generation in the normal dispersion regime by leveraging second-harmonic interactions, advancing integrated photonics for optical clocks.

Contribution

It introduces a new phase-matching approach using second-harmonic interactions for Kerr comb formation in normal dispersion microresonators, supported by theoretical and experimental validation.

Findings

Enables Kerr comb generation in normally prohibitive dispersion regimes.

Provides a new phase-matching mechanism via second-harmonic interaction.

Achieves qualitative agreement between simulations and experiments.

Abstract

Simultaneous Kerr comb formation and second-harmonic generation with on-chip microresonators can greatly facilitate comb self-referencing for optical clocks and frequency metrology. Moreover, the presence of both second- and third-order nonlinearities results in complex cavity dynamics that is of high scientific interest but is still far from well understood. Here, we demonstrate that the interaction between the fundamental and the second-harmonic waves can provide an entirely new way of phase-matching for four-wave mixing in optical microresonators, enabling the generation of optical frequency combs in the normal dispersion regime, under conditions where comb creation is ordinarily prohibited. We derive new coupled time-domain mean-field equations and obtain simulation results showing good qualitative agreement with our experimental observations. Our findings provide a novel way of overcoming the dispersion limit for simultaneous Kerr comb formation and second-harmonic generation, which might prove especially important in the near-visible to visible range where several atomic transitions commonly used for stabilization of optical clocks are located and where the large normal material dispersion is likely to dominate.