Topological phases in Kagome and triangular photonic crystals

Topological photonics facilitates the propagation of terahertz waves with extremely high transmission and without backscattering, even in the presence of sharp corners and defects. This study initiates by demonstrating the properties of protected topological states based on a Kagome lattice featuring air holes embedded within a silicon background. Additionally, an exploration of the crystalline symmetry establishes a correlation between Kagome and triangular lattices. These two lattice types, interconnected with the valley degrees of freedom, manifest distinct band gaps and operational modes. The robustness of topological edge states and corner states has been empirically verified. Furthermore, a hybridization of these lattices is employed to design a sandwich waveguide for encrypted transmission. Within this structure, the middle structure supports terahertz waves with different frequencies and modes and outputs the specific frequency and mode through the corresponding ports. Our work increases flexibility in manipulating terahertz waves and holds potential applications in the fields of topological photonics.