Dual‐Band Valley Hall Topological Photonic Crystal in the Terahertz Regime and Its Directional Radiation

ABSTRACT Valley‐Hall photonic crystals offer promising opportunities for topological wave routing, frequency‐selective manipulation, and directional radiation, yet most experimentally demonstrated terahertz (THz) systems operate within a single topological bandgap. Here, we propose and experimentally characterize a dual‐band valley‐Hall topological photonic crystal in the THz regime. By rotating triangular metallic scatterers in a hexagonal lattice, mirror symmetry is broken, and two topologically nontrivial bandgaps are opened under transverse‐magnetic polarization. Their valley topology is characterized by valley Chern numbers, Berry curvature, and chiral orbital angular momentum. Armchair‐ and zigzag‐type interfaces support kink states in both bandgaps, with simulations confirming robust transport through sharp bends. Spatially resolved THz time‐domain spectroscopy further reveals directional radiation from the dual‐band interface modes. Near‐field distributions measured 2 mm from the output facet agree well with simulations: distinct directional features appear in Gap 1, while spatial overlap and phase superposition produce interference fringes in Gap 2. These results establish a dual‐band valley‐Hall platform for frequency‐selective THz wave manipulation and directional beam control.