Abstract
We experimentally and theoretically investigate the dynamics of microresonator-based frequency comb generation assisted by mode coupling in the normal group-velocity dispersion (GVD) regime. We show that mode coupling can initiate intracavity modulation instability (MI) by directly perturbing the pump-resonance mode. We also observe the formation of a low-noise comb as the pump frequency is tuned further into resonance from the MI point. We determine the phase-matching conditions that accurately predict all the essential features of the MI and comb spectra, and extend the existing analogy between mode coupling and high-order dispersion to the normal GVD regime. We discuss the applicability of our analysis to the possibility of broadband comb generation in the normal GVD regime.
Highlights
IntroductionOptical frequency comb generation based on nonlinear microresonators [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24] is a rapidly evolving field of research that could potentially benefit such diverse fields as optical metrology, spectroscopy, optical waveform synthesis and telecommunications [6]
In comparison to the dynamics of the anomalous group-velocity dispersion (GVD) regime, the comb generation in the normal GVD regime is relatively unexplored. In this Article, we investigate in detail the dynamical behavior of comb generation triggered by mode coupling in a microresonator characterized by normal GVD
These results provide concrete evidence that mode coupling can manifest itself as effective high-order dispersion that breaks symmetry, leading to qualitatively similar features to those that were originally attributed to dispersive wave emission in anomalous-GVD resonators and demonstrating that the analogy between high-order dispersion and mode coupling can be generalized to the normal GVD regime
Summary
Optical frequency comb generation based on nonlinear microresonators [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24] is a rapidly evolving field of research that could potentially benefit such diverse fields as optical metrology, spectroscopy, optical waveform synthesis and telecommunications [6]. Mode coupling has been reported to aid comb generation in normal GVD microresonators [9, 14, 15, 17, 18] which in some cases corresponds to the formation of dark pulse-like structures in the time domain [18] This latter work hinted that mode coupling may be responsible for generating the initial MI sidebands in which phase-matching was achieved by shifting one of the sideband modes far away from the pump-resonance mode while allowing the pump to operate in the blue-detuned regime of the Kerr bistability and remain thermally stable [32]. We subsequently tune the pump frequency further into resonance and study the generated low-noise comb This comb exhibits spectral features similar to dispersive waves, and we explain them in terms of the analogy between high-order dispersion and mode coupling. The potential of broadband comb generation is discussed in this context
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