Large-area gapped edge states in a valley photonic crystal heterostructure

Recent works exploiting photonic valley Hall effect show that large-area topological states can be realized by inserting gapless photonic crystal structures into topological interfaces, thus effectively introducing mode width degree of freedom. However, the previously reported works focus on gapless edge states. It is rare to investigate gapped edge states, especially large-area gapped edge states. In this paper, large-area gapped edge states in a valley photonic crystal heterostructure are achieved and experimentally proved. Compared with large-area gapless topological states, the present gapped edge states are more localized, which provides a more effective way to manipulate electromagnetic waves. We implement a topological energy concentrator and topological resonator cavity based on the large-area topological transmission with the gapped edge states. It is expected that our results broaden photonic systems, which can be used in topological lasing, field enhancement, and high-capacity energy transport.