Walk-off controlled self-starting frequency combs in CH(2) optical microresonators

Investigations of frequency combs in CH(3) optical microresonators are burgeoning nowadays. Changeover to CH(2) resonators promises further advances and brings new challenges. Here, the comb generation entails not only coupled first and second harmonics (FHs and SHs) and two dispersion coefficients, but also a substantial difference in the group velocities - the spatial walk-off. We predict walk-off controlled highly stable comb generation, drastically different from that known in the CH(3) case. This includes the general notion of antiperiodic state, formation of coherent antiperiodic steady states (solitons), where the FH and SH envelopes move with a common velocity without shape changes, characterization of the family of antiperiodic steady states, and the dependence of comb spectra on the pump power and the group velocity difference.