Integrated Backward Second-Harmonic Generation through Optically Induced Quasi-Phase-Matching

Quasi-phase-matching for efficient backward second-harmonic generation requires sub-μm poling periods, a nontrivial fabrication feat. For the first time, we report integrated first-order quasiphase-matched backward second-harmonic generation enabled by seeded all-optical poling. The self-organized grating inscription circumvents all fabrication challenges. We compare backward and forward processes and explain how grating period influences the conversion efficiency. These results showcase unique properties of the coherent photogalvanic effect and how it can bring new nonlinear functionalities to integrated photonics.