Valley topological line-defects for Terahertz waveguides and power divider

Topological edge states exhibit low backscattering, unidirectional energy propagation, and robust immunity to sharp bends and defects in photonic topological waveguides. These properties of topological waveguides are expected to be applied in terahertz (THz) technology and expand to functional devices. Here, we introduce a line-defect into valley Hall photonic crystals (VPCs) and discuss the influence of line-defect to edge states of valley Hall photonic topological waveguide. The introduction of line-defect can greatly improve the design freedom of topological waveguides, and is expected to be extended to functional devices. We constructed a straight VPC waveguide and a Z-shaped VPC waveguide to verify the topological valley line-defect edge state and the single-mode transmission of topological line-defect states is excited by a rectangular waveguide with a tapered coupling structure. The VPC waveguide has low bending loss and a working bandwidth (return loss < −10 dB) from 0.4 to 0.422 THz. We propose a topological power divider (TPD) operating at THz frequencies and achieved −3.3 per port equal power divide. Furthermore, this TPD is robust against defects and is promising for on-chip THz integration.