Optically reconfigurable quasi-phase-matching in silicon nitride microresonators

Bringing efficient second-order nonlinear effects in integrated photonics is an important task motivated by the prospect of enabling all possible optical functionalities on chip. Such has proved particularly challenging silicon photonics, as materials best suited for photonic integration lack susceptibility ($\chi^{(2)}$). Methods inducing effective $\chi^{(2)}$ such have recently opened new opportunities. Here, we present optically reconfigurable quasi-phase-matching large radius Si$_3$N$_4$ microresonators resulting mW level on-chip second-harmonic generated powers. Most importantly show that all-optical poling can occur unconstrained from intermodal phase-matching, leading to widely tunable generation. We confirm phenomenon two-photon imaging inscribed grating structures within well dynamic tracking both pump and mode resonances. These results unambiguously establish photogalvanic effect, responsible poling, overcome phase mismatch constraints even resonant systems, simultaneously allow combined record output power tunability.