Optically reconfigurable quasi-phase-matching in silicon nitride microresonators

Quasi-phase-matching has long been a widely used approach in nonlinear photonics, enabling efficient parametric frequency conversions such as second-harmonic generation. However, in silicon photonics the task remains challenging, as materials best suited for photonic integration lack second-order susceptibility (chi((2))), and means for achieving momentum conservation are limited. Here we present optically reconfigurable quasi-phase-matching in large-radius silicon nitride microresonators, resulting in up to 12.5-mW on-chip second-harmonic generated power and a conversion efficiency of 47.6% W-1. Most importantly, we show that such all-optical poling can occur unconstrained from intermodal phase-matching, leading to broadly tunable second-harmonic generation. We confirm the phenomenon by two-photon imaging of the inscribed chi((2)) grating structures within the microresonators as well as by in situ tracking of both the pump and second-harmonic mode resonances during all-optical poling. These results unambiguously establish that the photogalvanic effect, responsible for all-optical poling, can overcome phase mismatch constraints, even in resonant systems. Photogalvanic effect in silicon nitride microresonators enables reconfigurable quasi-phase-matching for efficient and tunable second-harmonic generation.

Automated summary

In this study, optically reconfigurable quasi-phase-matching is proposed in large-radius silicon nitride microresonators for efficient and tunable second-harmonic generation in silicon photonics. The photogalvanic effect is shown to overcome phase mismatch constraints, even in resonant systems.