Topological transitions in continuously-deformed photonic crystals

TL;DR

This paper explores how continuous geometric deformations in 2D dielectric photonic crystals induce multiple topological transitions, enabling sensitive control over edge states for potential optical sensing and waveguiding applications.

Contribution

It demonstrates multiple topological transitions in simple 2D photonic crystals through geometric modifications, revealing their potential for optical sensors and unidirectional waveguides.

Findings

Multiple topological transitions can be induced by changing hole radii and spacing.

Topological photonic band gaps resemble quantum spin-Hall insulators.

Optimized structures show large band gaps with robust edge states.

Abstract

We demonstrate that multiple topological transitions can occur, with high-sensitivity, by continuous change of the geometry of a simple 2D dielectric-frame photonic crystal consisting of circular air-holes. By changing the radii of the holes and/or the distance between them, multiple transitions between normal and topological photonic band gaps (PBGs) can appear. The time-reversal symmetric topological PBGs resemble the quantum spin-Hall insulator of electrons and have two counter-propagating edge states. We search for optimal topological transitions, i.e., sharp transitions sensitive to the geometry, and optimal topological PBGs, i.e., large PBGs with clean spectrum of edge states. Such optimizations reveal that dielectric-frame photonic crystals are promising for optical sensors and unidirectional waveguides.