Multi-Type Topological States in Higher-Order Photonic Insulators Based on Kagome Metal Lattices

Tunability of topological photonic structures opens a new avenue for photonics research. The rich physical characteristics of the topological photonics have great significance in practical implementations. In this paper, multi-type topological states are demonstrated in higher-order photonic topological insulators based on Kagome metal lattices. By stretching or rotating Kagome metal lattices, two types of topological insulators are obtained, and multi-type topological states are observed. By stretching Kagome metal lattices, a 1D topological edge state and two types of higher-order topological corner states (corresponding to a traditional higher-order topological corner state based on nearest-neighbor coupling and a new higher-order corner state caused by long-range interactions) are obtained in a classical quantization of dipole moments higher-order topological insulators. By rotating Kagome metal lattices, dual-band higher-order valley-Hall topological insulators are achieved with nodal ring degeneracy. Odd-type and even-type topological states are obtained. Achieving reconfigurable, multi-type, and multi-band topological insulators by using a single structural unit provides interesting insights into topological photonics and provides an unconventional approach to explore photonic systems and condensed matter physics.