Valley-Hall-like second-order photonic topological insulators in Kagome lattice

TL;DR

This paper introduces a new class of second-order photonic topological insulators in Kagome-lattice photonic crystals, featuring topological invariants based on electric polarization and supporting edge and corner states for robust photonic applications.

Contribution

It demonstrates the design of valley-Hall-like second-order topological insulators with quantized electric polarization in Kagome photonic crystals, expanding topological photonics beyond Chern number characterization.

Findings

Topological phase transition achieved by tuning structural size.

Presence of topologically protected edge states at interfaces.

Support for zero-dimensional corner states indicating second-order topology.

Abstract

Valley-Hall-like second-order photonic topological insulators are designed in Kagome-lattice photonic crystals with C3v point-group symmetry. The photonic crystal consists of circular air holes in pure dielectric materials. Different from conventional valley-Hall photonic topological insulators characterized by valley Chern numbers, the proposed insulators have topological invariants described by quantized electric polarization. Topological transition can be realized by tuning the structural size and topological edge states appear at the interface between photonic crystals with different topological phases, preserving important features of valley-Hall photonic insulators such as valley transport with little backscattering. The proposed photonic crystal also support zero-dimensional corner states in oblique corners, showing its second-order topological insulator signature. This work presents the possibility to realize topologically protected reflection suppressed waveguides and local cavities in the same platform.