Second harmonic generation enhancement and directional emission from topological corner state based on the quantum spin Hall effect

Topological corner state has attracted much research interests since it does not obey the conventional bulk-edge correspondence and enables tightly confined light within small volumes. In this work, we demonstrate an enhanced second harmonic generation (SHG) from a topological corner state and its directional emission. To this end, we design an all-dielectric topological photonic crystal based on optical quantum spin Hall effect. In this framework, pseudospin states of photons, topological phase, and topological corner state are subsequently constructed by engineering the structures. It is shown that a high Q-factor of 3.66x10(11) can be obtained at the corner state, showing strong confinement of light at the corner. Consequently, SHG is significantly boosted and manifests directional out-of-plane emission. More importantly, the enhanced SHG has robustness against a broad class of defects. These demonstrated properties offer practical advantages for integrated optical circuits. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Automated summary

Enhanced second harmonic generation (SHG) and directional emission can be achieved from a topological corner state in an all-dielectric topological photonic crystal, showing a high Q-factor and strong confinement of light at the corner. The enhanced SHG also exhibits robustness against a broad class of defects, offering practical advantages for integrated optical circuits.