Topologically Protected Edge States in Valley Photonic Crystals for Terahertz Waveguiding

Topological photonics has been a main focus of research since the breakthrough in Topological Insulators (TIs), largely because of its intrinsic properties such as robustness against disorders and defects. Valleytronics, leveraging the valley degree of freedom, is an interesting approach where the valley-locked excited edge modes propagate without any intervalley mixing. This enables retaining maximum fraction of the incoming signal to the output, ensuring high signal integrity and efficiency. We utilise this concept of valleytronics and deisgn a novel waveguide structure which exhibits superior transmission in the frequency range of 298 - 328 GHz. Upon breaking the symmetry of the Valley Photonic Crystals (VPCs), valley-locked edge states appear inside the band gap spanning a 30 GHz opening. The robustness of these edge states are demonstrated for a straight and a zig-zag waveguiding path which yield an average transmission of -2.98 dB and -3.12 dB, respectively. This could have potential applications in integrated terahertz topological passive devices.