Topological Large-Area Waveguide and Corner States in Kagome-Lattice Terahertz Photonic Crystals

Topological edge and corner states show great promise for manipulating electromagnetic waves, but their limited mode area restricts practical applications. Here, we propose a topological terahertz photonic crystal with a three-layer heterostructure, in which the middle Dirac photonic crystal layer that exhibits Dirac-like dispersion supports large-area terahertz waveguide states. Quantitative analysis shows that valley-momentum-locked states maintain high transmission even at sharp bends and in the presence of defects. Additionally, we demonstrate topological large-area corner modes. The mode area scales with the number of photonic crystal layers that exhibit Dirac-like dispersion, as confirmed by numerical calculations. This work advances the flexible control of terahertz waves and holds significant potential for practical applications in topological photonics.