Manipulation of coupling between waveguide and ring resonator in topological photonic crystals

Topological photonic crystals (TPCs) have attracted much attention as an excellent platform for manipulating light propagation. Waveguide and ring resonator are basic components in the all-optical integrated optical devices. In this paper, we construct TPCs based on elliptic dielectric columns and demonstrate that TPCs support broadband edge states with the properties of unidirectional propagation and robustness to structural defects. The topological ring resonator is realized utilizing TPCs, and possesses different resonant modes. Further, coupling between topological edge state and ring resonator has been researched with different resonant modes. In the topological waveguide-resonator system, when the frequency of the topological edge state is consistent with the resonant frequency of the ring resonator, the light can be coupled into the ring resonator with diverse coupling phenomena for traveling mode and standing mode. Moreover, a topological optical band-pass filter and a topological optical add/drop filter can be implemented, which can be applied in integrated optical devices.