# Pseudospin-Polarized Topological Line Defects in Dielectric Photonic Crystals

## TL;DR

This paper introduces a topological electromagnetic system with pseudospin-polarized line defect states in photonic crystals, enabling robust, unidirectional light propagation that is resistant to structural disorder.

## Contribution

It proposes a novel topological photonic system with pseudospin-polarized line defect states and demonstrates their stable, unidirectional energy flow in dielectric photonic crystals.

## Key findings

- Pseudospin-polarized topological line-defect states are identified.
- Unidirectional propagation is demonstrated and remains stable under disorder.
- States can be excited using spatially-symmetric line-source arrays with orbital angular momentum.

## Abstract

Electromagnetic topological insulators have been explored extensively due to the robust edge states they support. In this work, we propose a topological electromagnetic system based on a line defect in topologically nontrivial photonic crystals (PCs). With a finite-difference supercell approach, modal analysis of the PCs structure is investigated in detail. The topological line-defect states are pseudospin polarized and their energy flow directions are determined by the corresponding pseudospin helicities. These states can be excited by using two spatially-symmetric line-source arrays carrying orbital angular momenta. The feature of the unidirectional propagation is demonstrated and it is stable when disorders are introduced to the PCs structure.