Polymer valley photonic crystals with honeycomb structures for terahertz waveguides

Terahertz (THz) band has promising applications in next-generation wireless communications and new sensing technologies. However, the on-chip transmission of THz waves will encounter strong scattering at sharp corner structures of waveguides. Recently, valley photonic crystals (VPC) offer new possibilities for high-fidelity transmission of THz wave along complex shape waveguides. The VPC-based waveguide overcomes defects and sharp corners, probably resulting in high-performance on-a-chip THz devices. The THz VPC with polymer materials can be easy and low-cost building with 3D printing technology. In this paper, the VPC waveguides operating around 300 GHz are constructed using honeycomb lattices on a thin polymer plate. The mirror symmetry is broken by proper air-circular apertures located in the honeycomb lattice with a nontrivial band structure. Then the influences on the band structure by the polymer refractive index ranging from 1.5 similar to 2.0, the thickness of the sheet, and the asymmetry of aperture diameters in the lattice are discussed. The transmission of straight, zigzag, and "omega"waveguides made of the polymer VPCs is simulated. The results demonstrate their high transmission efficiency and robustness to scattering from sharp bending above -10 dB with an 8-GHz bandgap. The proposed polymer VPC structure paves way for THz applications such as efficient beam splitters, low-loss complex-shaped waveguides, and robust delay lines.