Optimization and robustness of topological corner state in second-order topological photonic crystal

TL;DR

This paper explores the optimization and robustness of topological corner states in second-order topological photonic crystals, achieving high quality factors and demonstrating resilience against various disorders, paving the way for advanced nanophotonic devices.

Contribution

It presents the first combined theoretical and experimental optimization of topological corner states, achieving record quality factors and demonstrating robustness against disorders.

Findings

Maximum quality factor of about 6000 achieved

Corner states are robust against bulk, edge, and corner defects

Optimization methods include structural modifications and surface passivation

Abstract

The second-order topological photonic crystal with 0D corner state provides a new way to investigate cavity quantum electrodynamics and develop topological nanophotonic devices with diverse functionalities. Here, we report on the optimization and robustness of topological corner state in the second-order topological photonic crystal both in theory and in experiment. The topological nanocavity is formed based on the 2D generalized Su-Schrieffer-Heeger model. The quality factor of corner state is optimized theoretically and experimentally by changing the gap between two photonic crystals or just modulating the position or size of the airholes surrounding the corner. The fabricated quality factors are further optimized by the surface passivation treatment which reduces surface absorption. A maximum quality factor of the fabricated devices is about 6000, which is the highest value ever reported for the active topological corner state. Furthermore, we demonstrate the robustness of corner state against strong disorders including the bulk defect, edge defect, and even corner defect. Our results lay a solid foundation for the further investigations and applications of the topological corner state, such as the investigation of strong coupling regime and the development of optical devices for topological nanophotonic circuitry.