On excitation of breather solitons in an optical microresonator.

We theoretically investigate mode-locked regimes of optical-frequency combs generated in a nonlinear ring microresonator pumped with continuous-wave light. We find that breather solitons can be formed in the resonator for certain values of frequency and power of the pump. We argue that relatively slow modulation of the comb-frequency harmonics observed in several recent experiments can be attributed to soliton formation.