Multifunctional Coupling System of Topological Edge Waveguide and Corner State Cavity Based on Honeycomb Photonic Crystals

Recently, the topological edge waveguide and corner state cavity have attracted the extensive attention of researchers due to their excellent characteristics with robustness to defects and localization to cavity in manipulating signal transmission, respectively. Herein, topologically trivial and nontrivial photonic crystals (PCs) are realized by shrinking and expanding the honeycomb lattice, and achieve gapped and continuous edge states in the constructed topological edge waveguides with zig-zag and armchair interfaces by combining two kinds of PCs with different topologies, respectively. In addition, corner states are realized by constructing box-shaped structure with zig-zag interfaces, and verify that the corner states appearing around the obtuse-angle corners are topologically protected to introduced defects in the structure. Moreover, a waveguide-cavity coupling system based on an armchair waveguide and a rhomboid cavity is proposed, which can realize multifunction of the signal delay and filtering at specific frequencies. Furthermore, a coupling system consisting of two waveguide and a cavity is constructed to implement beam splitting and filtering, and the stability of the system is greatly improved compared with the traditional optical devices because of the topological property. This work presents a novel approach for the design of micro-nano integrated photonic devices such as filters, storages, and splitters.