Dynamics of mode-coupling-induced microresonator frequency combs in   normal dispersion
  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. 
Jae K. Jang, Yoshitomo Okawachi, Mengjie Yu, Kevin Luke, Xingchen Ji,   Michal Lipson, and Alexander L. Gaeta
physics.optics