Manipulation of coupling between topological edge state and corner state in photonic crystals

Abstract

Topological photonic crystals whose topological protection makes them very robust against perturbations offer a new way of manipulating photons in micro/nano-photonic devices. In this paper, we propose a type of topological photonic crystal (PC) system with a square lattice, and we demonstrate that topological edge state (TES) and topological corner state (TCS) can coexist in the PC resonator. Coupling between the TES and TCS can be achieved in a system with a topological PC waveguide and a box-shaped topological PC resonance cavity. The results indicate that air defects introduced in the box-shaped resonator will lead to the frequency shift of TCS. These air defects can be used to narrow the bandwidth and to increase the quality factor Q of the Fano resonance system. In addition, the resonance energy coupled from the TES to the TCS is greatly enhanced by the introduction of the air defects in the box-shaped resonance cavity. This work paves a new approach for the development of topological integrated optical devices with high quality factor and strong coupling.