Kerr comb generation in a whispering gallery mode microcavity: The effect of mode coupling

Abstract

Optical Kerr comb source on chip by using a whispering gallery mode (WGM) microcavity is gaining attention due to the small size and low power. The generation of Kerr comb is based on a cascaded four-wave mixing (FWM), and the system exhibit a pulsed output when the generated comb is in a mode-locked state. The time-domain picture of the mode-locking is explained by circulating a soliton pulse in the WGM microcavity that has anomalous dispersion. Although a low-noise mode-locked output is preferred, it is often difficult to achieve, due to various phenomena simultaneously taking place in a WGM microcavity system. For instance, the optical mode in a toroid WGM microcavity easily couples with a mechanical mode via cavity opto-mechanics. It significantly influences the stability of the output. We need to investigate a way to suppress the mechanical motion in order to obtain stable output, which will be discussed in this talk. Other issues are the coupling of CW and CCW modes, and the interplay between the Raman scattering and FWM. In this talk, I will share on our investigation on how these effect influence the output and ways to control them. In addition, I will also show our recent experiment on broadband visible comb generation using a silica toroid WGM microcavity system via third-harmonic generation.