Large-area quantum-spin-Hall waveguide states in a three-layer topological photonic crystal heterostructure

TL;DR

This paper demonstrates the creation of large-area topological waveguide states in a three-layer photonic crystal heterostructure using photonic analogs of quantum spin Hall effect, with implications for robust, large-scale photonic devices.

Contribution

It introduces a novel method to generate large-area topological helical waveguide states employing the photonic quantum spin Hall effect in a three-layer heterostructure.

Findings

Large-area topological helical waveguide states are achieved in a three-layer photonic crystal.

A power-law relationship between bandgap size and middle domain width is established.

Robust, unidirectional propagation with pseudospin-momentum locking is demonstrated.

Abstract

Topological photonic edge states are conventionally formed at the interface between two domains of topologically trivial and nontrivial photonic crystals. Recent works exploiting photonic quantum Hall and quantum valley Hall effects have shown that large-area topological waveguide states could be created in a three-layer topological heterostructure that consists of a finite-width domain featuring Dirac cone sandwiched between two domains of photonic crystals with opposite topological properties. In this work, we show that a new kind of large-area topological waveguide states could be created employing the photonic analogs of quantum spin Hall effect. Taking the well-used Wu-Hu model in topological photonics as an example, we show that sandwiching a finite-width domain of photonic crystals featuring double Dirac cone between two domains of expanded and shrunken unit cells could lead to the emergence of large-area topological helical waveguide states distributed uniformly in the middle domain. Importantly, we unveil a power-law scaling regarding to the size of the bandgap within which the large-area helical states reside as a function of the width of the middle domain, which implies that these large-area modes in principle could exist in the middle domain with arbitrary width. Moreover, pseudospin-momentum locking unidirectional propagations and robustness of these large-area waveguide modes against sharp bends are explicitly demonstrated. Our work enlarges the photonic systems and platforms that could be utilized for large-area-mode enabled topologically waveguiding.