  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.
