Far-field detection of two-dimensional terahertz topological photonic crystals

Originating from the investigation of condensed matter states, we have discovered a new material with phase transition no-trivial properties——topological insulators. With the progress in artificial metamaterials, the photonic crystals which can give rise to topological edge states that propagate around sharp corners immune to scattering have captured much attention. In this paper, according to the spatial and time reversal symmetry and quantum spin Hall effect theory, we presented a topological photonic crystal made of metallic cylinders at terahertz frequencies. By slightly expanding and shrinking the unit cell, the spatial reversal symmetry was broken and therefore, the band degeneracy was broken, realizing the topological band gap. Unidirectional topological edge states were proven to exist on a domain wall connecting two photonic crystals with opposite topological properties without back-scattering. Then we investigated the reflection spectra of the designed topological photonic crystals in the terahertz regime, which provided a new means to verify topological photonic crystals.