# Topological Photonics on a Small Scale

## TL;DR

This paper explores how topological photonics can be applied on small scales, enabling robust optical devices that are less affected by structural imperfections.

## Contribution

The paper highlights recent advances in subwavelength topological photonics and introduces a novel platform using higher-order topological effects.

## Key findings

- Topological states can be realized using arrays of resonant nanoparticles at small scales.
- Higher-order topological effects enable highly efficient optical cavities below the wavelength of light.
- Topological polaritonic structures show promise for robust nanoscale photonic applications.

## Abstract

The study of topological phases of light suggests novel opportunities for creating robust optical structures and on‐chip photonic devices which are immune against scattering losses and structural disorder. However, many recent demonstrations of topological effects in optics use structures with relatively large scales. Here, the physics and realization of topological photonics on small scales, with the dimensions often smaller or comparable with the wavelength of light, are discussed. The recent experimental demonstrations of small‐scale topological states based on arrays of resonant nanoparticles are highlighted and a novel photonic platform using higher‐order topological effects for creating subwavelength highly efficient topologically protected optical cavities is discussed. Special attention is paid to the recent progress on topological polaritonic structures and the paper concludes with the vision on the future directions of nanoscale topological photonics and its impact on other fields.

In this Perspective, the recent advances in small‐scale topological photonics based on low‐dimensional localized states supported by subwavelength optical structures are discussed. The key achievements in this field are summarized and an outlook of the future progress of small‐scale topological nanophotonics is provided.© 2021 WILEY‐VCH GmbH