Large-area quantum-spin-Hall waveguide states in a three-layer topological photonic crystal heterostructure

Topological photonic edge states usually are formed at the interface between two domains of topologically trivial and nontrivial photonic crystals. The authors propose topological waveguide states with tunable widths in a three-layer topological photonic crystal heterostructure, which exhibit a helical pseudospin-momentum locking feature of the quantum spin Hall effect.