Manipulation of photonic topological edge and corner states via trivial claddings

TL;DR

This paper demonstrates how trivial claddings can be used to manipulate topological edge and corner states in photonic crystals, revealing a new method to control topological boundary phenomena through geometric tuning.

Contribution

It introduces a novel approach to manipulate topological boundary states in photonic crystals by tuning trivial claddings, highlighting their crucial role in topological phase transitions.

Findings

Topological interface states undergo phase transition with geometric tuning of trivial cladding.

Corner states depend critically on the trivial cladding, indicating higher-order topology.

Experimental demonstration confirms the role of trivial claddings in topological state formation.

Abstract

Crystalline symmetry offers a powerful tool to realize photonic topological phases, in which additional trivial claddings are typically required to confine topological boundary states. However, the utility of the trivial cladding in manipulating topological waves is often overlooked. Here, we demonstrate two topologically distinct kagome photonic crystals (KPCs) based on different crystalline symmetries: \mathbit{C}_\mathbf{6}- symmetric KPCs exhibit a quantum spin Hall phase, while \mathbit{C}_\mathbf{3}-symmetric KPCs serve as trivial cladding. By tuning the geometric parameter of the trivial cladding, we observe that a pair of topological interface states featured with pseudospin-momentum locking undergoes a phase transition, accompanied by the appearance and disappearance of corner states in a finite hexagonal supercell. Such a geometry-induced band inversion is characterized by a sign change in the Dirac mass of the topological interface states and holds potential for applications such as rainbow trapping. Furthermore, we experimentally demonstrate the corner states, which is a hallmark of higher-order topology, also depend critically on the trivial cladding. Our work highlights the crucial role of trivial claddings on the formation of topological boundary states, and offers a novel approach for their manipulation.