# Higher-order photonic topological states in surface-wave photonic crystals

## TL;DR

This paper demonstrates a planar surface-wave photonic crystal that realizes two-dimensional higher-order topological insulators, featuring large bandgaps and zero-dimensional corner states, advancing integrated photonics applications.

## Contribution

The work introduces a novel planar design for higher-order photonic topological insulators with large bandgaps, overcoming previous limitations of frequency range and size.

## Key findings

- Large bulk bandgap of 28% due to multiple Bragg scatterings
- Presence of one-dimensional gapped edge states
- Emergence of zero-dimensional corner states

## Abstract

Photonic topological states have revolutionized our understanding on the propagation and scattering of light. Recent discovery of higher-order photonic topological insulators opens an emergent horizon for zero-dimensional topological corner states. However, the previous realizations of higher-order photonic topological insulators suffer from either a limited operational frequency range due to the lumped components involved or a bulky structure with a large footprint, which are unfavorable for future integrated photonics. To overcome these limitations, we hereby experimentally demonstrate a planar surface-wave photonic crystal realization of two-dimensional higher-order topological insulators. The surface-wave photonic crystals exhibit a very large bulk bandgap (a bandwidth of 28%) due to multiple Bragg scatterings and host one-dimensional gapped edge states described by massive Dirac equations. The topology of those higher-dimensional photonic bands leads to the emergence of zero-dimensional corner states, which provide a route toward robust cavity modes for scalable, integrated photonic chips and an interface for the control of light-matter interaction.

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Source: https://tomesphere.com/paper/1901.07154