Effect of asymmetry on terahertz transmissions in topological photonic crystals comprising of dielectric rod structures

Abstract

We numerically demonstrate robust terahertz (THz) transmissions in a topological photonic crystal comprised of dielectric rod structures. Topological edge states (i.e., the vortex states) in the structure are excited via a zig-zag domain boundary at the interface of two nontrivial valley photonic crystals (VPCs). A comprehensive study of the effect of asymmetry (defined as δd=d1−d2) on transmission loss and bandwidth is performed for three different kinds of domain boundaries: straight, Z-shape, and Ω-shape. An increase in the bandwidth of the topological THz transmission is achieved with the increasing asymmetry. The study further demonstrates blue shifting of the topological transmission bandwidth with the increase in asymmetry. An optimized value of the asymmetry parameter is obtained based on the bandwidth as well as the transmission loss. The most robust propagation in terms of the widest bandwidth and low loss transmission is achieved with asymmetry ≥0.25a. The robust THz transmission is attributed to the strong edge modes confinement at the domain boundary of the VPC due to intervalley scattering suppression at this optimal value. Our observations open the path for a strong electromagnetic wave flow in the THz regime with a high transmission, which could be useful in photonic broadband communication and other on-chip applications at THz frequencies, particularly for 6G communications.