Influence of medium column type on edge states in all-media topological photonic crystals

Abstract

We have constructed photonic crystals (PCs) of a standard honeycomb lattice composed of solid dielectric columns, hollow dielectric columns, and composite dielectric columns and studied the influence of their dielectric constant and filling ratio on the topological boundary states. The optical quantum spin Hall effect is realized by compressing and stretching the standard honeycomb lattice. In the waveguide structure with sharp bends, cavity, and disorder, the electromagnetic (EM) wave is transmitted unidirectionally and robustly, which verifies the transmission characteristics of the topological edge states. In addition, by replacing several solid dielectric columns near the junction of PCs with different topological states with composite dielectric columns, disturbance is introduced to the edge states, and the influence of the relative effective permittivity of the composite dielectric columns on the edge states is studied. It is found that the EM wave in the gap between the upper boundary state and the lower boundary state cannot be transmitted, and with the increase of the relative effective permittivity of the composite dielectric columns, the gap becomes larger and larger, and the position of the gap gradually moves down. Based on this, a photonic crystal (PC) waveguide structure that has higher transmission efficiency, robust unidirectionality, and higher optical localization performance, is designed. It has more potential development in filters, optical switches, optical communication systems, and semiconductor technology.