Fig. 1. Basic properties of THz VPC. (a) Schematic diagram of the VPC structure; (b) unit cell structure of VPC 1 with C₆ symmetry, while the unit cell structures of VPC 2 and VPC 3 are C₃ symmetry; (c) energy band structure of VPC; (d) magnetic field H_zphase situations and Poynting vector distributions (black arrows) at the K (K') point for VPC 2 and VPC 3

Fig. 2. Tunable THz VPC topological edge states with LC resonator. (a) Schematic diagram of the beard-shaped topological edge; (b) projected energy band; (c) electric field distributions of topological edge states at different labeled points

Fig. 3. Tunable characteristics of Z-shaped topological edge states with LC. (a) Z-shaped topological waveguide structure, with star showing the position of the THz vortex source, and LC resonators filled in the two boundary paths; (b) setting up of the THz vortex source; (c) transmission spectra of Z-shaped waveguide with refractive index n=1.0, 1.5, and 1.8 in the boundary cavity (d) electric field distributions of the Z-shaped waveguide at 0.990 THz and 1.005 THz when n=1.0, 1.5, and 1.8

Fig. 4. Tunable characteristics of Z-shaped waveguide transmittance with LC. (a) Tunable transmission of the TESs in the Z-shaped waveguide at 0.990 THz; (b) THz electric field diagrams for n=1.5, 1.6, 1.7, and 1.8, respectively

Fig. 5. Tunable THz VPC wavelength division multiplexer with LC resonator. (a) Schematic diagram of the WDM structure, the upper and lower ITO transparent electrodes are spin-coated with SD 1 as the orientation layer for LC, when a bias voltage is applied, the orientation of LC changes from horizontal to vertical; (b) electric field distributions at 0.990 THz when the refractive index of LC is 1.5 and 1.7, respectively; (c) tunable transmission of the two output ports at 0.990 THz

Fig. 6. Effects of defect on transmission. (a) Electric field distribution in the THz wavelength division multiplexer with a point defect at the interface (0.990 THz, n=1.5); (b) THz transmission spectra with/without the point defect (n=1.5)