Dual-polarization helical interface states in inverse-designed photonic crystals with glide symmetry

Abstract

Photonic analogs of topological crystalline insulators (PTCIs) that host pseudospin-locked unidirectional helical interface states have promising applications for developing novel integrated optical devices. However, current PTCIs are limited to a single polarization. Here, we propose a dual-polarization PTCI hosting topological interface states for both transverse electric (TE) and transverse magnetic (TM) modes. First, we design a photonic crystal (PC), constrained with glide symmetry, with a dual-polarization bulk gap via inverse design. Then, by adopting two kinds of unit cells with different topology indexes from the PC and arranging them to form an interface, pseudospin-locked unidirectional helical interface states are observed. Pseudospin-locked one-way propagations of edge states for both TE and TM modes are demonstrated. Besides the polarization-independent function, we also present the polarization-dependent propagation of interface states by tuning the frequency. Our work demonstrates the flexible manipulation of light in PTCIs with the polarization degree of freedom, having promising applications in developing both polarization-independent and polarization-dependent topological optical devices.