Coexisting valley and pseudo-spin topological edge states in photonic topological insulators made of distorted Kekule lattices

Photonic topological insulators protected by the lattice spatial symmetry (e.g., inversion and rotation symmetry) mainly support single type edge state, interpreted by either valley or pseudo-spin. Here, we demonstrate theoretically, numerically, and experimentally that a type of judiciously designed two-dimensional Kekule photonic crystal with time reversal symmetry can possess topological valley and pseudo-spin edge states in different frequency bands. Topologically robust transportation of both the valley and pseudo-spin edge states was confirmed by measuring the transmission of straight and z-shaped interface supported edge mode and comparing with bulk modes in the microwave frequency regime. In addition, we show that due to the distinct topological origins, valley and pseudo-spin edge states can be distinguished by examining their end-scattering into the free space. Our system provides an alternative way in manipulating electromagnetic waves with additional degree-of-freedom, which has potential applications for robust and high-capacity waveguiding and multi-mode dividing. (C) 2022 Chinese Laser Press

Automated summary

This study demonstrates the existence of topological valley and pseudo-spin edge states in a carefully designed two-dimensional Kekule photonic crystal with time reversal symmetry. The presence of these edge states was confirmed through theoretical, numerical, and experimental analysis, and their distinct characteristics were identified through transmission measurements and end-scattering analysis.