AlGaAs waveguide microresonators for efficient generation of quadratic frequency combs

We propose a flexible design for directional quasi-phase-matching in AlGaAs waveguide resonators implementing the recently demonstrated optical frequency combs in cavity-enhanced second-harmonic generation. We numerically study the onset of internally pumped optical parametric oscillations that trigger the subsequent comb formation. We also perform a coherence analysis of a particular class of numerically simulated optical frequency combs, corresponding to stable temporal cavity field patterns, revealing the high degree of coherence associated with such stable solutions, a key feature for many refined applications of optical frequency combs. Our analysis shows that efficient generation of coherent frequency combs is possible with threshold powers in the microwatt range and path lengths up to several millimeters, thus enabling the practical realization of new on-chip frequency comb synthesizers, fully integrable in more complex photonic circuits.