Harmonic mode locking in a high-Q whispering gallery mode microcavity

TL;DR

This paper investigates harmonic mode locking in a high-Q whispering gallery mode microcavity, combining numerical simulations and experiments to reveal a simple method for stable harmonic locking via power reduction.

Contribution

It demonstrates a new approach to achieve stable harmonic mode locking in microcavities without precise wavelength detuning adjustments.

Findings

Stable harmonic mode locking can be achieved by reducing input power after strong pumping.

Numerical and experimental results show low-noise Kerr comb spectra at low mode spacing.

The method simplifies the generation of harmonic mode locking in high-Q microcavities.

Abstract

A numerical and experimental study of the generation of harmonic mode locking in a silica toroid microcavity is presented. We use a generalized mean-field Lugiato-Lefever equation and solve it with the split-step Fourier method. We found that stable harmonic mode locking regime can be accessed when we reduce the input power after strong pumping even when we do not carefully adjust the wavelength detuning. This is due to the bistable nature of the nonlinear cavity system. The experiment agrees well with the numerical analysis, where we obtain low-noise Kerr comb spectrum at low longitudinal mode spacing by gradually reducing the pumping input after strong pumping. This finding clarifies the procedure for generating harmonic mode locking in such high-Q microcavity systems.