Variation of Topological Edge States of 2D Honeycomb Lattice Photonic Crystals

Herein, the photonic quantum spin Hall effect is realized in a dielectric 2D honeycomb lattice photonic crystal (PC) with scatterers having various shapes, by stretching and shrinking the honeycomb unit cell. The topological edge states and their unidirectional transmission as scatterers with triangular, pentagonal, and heptagonal shapes are studied. The unidirectional transmission in an inverted omega-shaped waveguide, when different types of defects are incorporated, is realized to verify the characteristics of the topological protection. Moreover, flat band can be realized by varying the shape of several scatterers near the combined junction of PCs with different topological states, and the variation trend of flat band is evaluated with the increase in the edge number of varied scatterers from four to seven at different times. Moreover, a slow-light waveguide is designed to further demonstrate the influence of the shape of scatterers on topological edge states for light transmission. Furthermore, the novel optical phenomenon of static state is realized; that is, light is not able to transmit but is trapped at the original position. This can increase the adjustability of the topological edge states and provide more potential applications for integrated photonic devices.