A numerical and experimental study of the generation of harmonic mode lockingin a silica toroid microcavity is presented. We use a generalized mean-fieldLugiato-Lefever equation and solve it with the split-step Fourier method. Wefound that stable harmonic mode locking regime can be accessed when we reducethe input power after strong pumping even when we do not carefully adjust thewavelength detuning. This is due to the bistable nature of the nonlinear cavitysystem. The experiment agrees well with the numerical analysis, where we obtainlow-noise Kerr comb spectrum at low longitudinal mode spacing by graduallyreducing the pumping input after strong pumping. This finding clarifies theprocedure for generating harmonic mode locking in such high-Q microcavitysystems.
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