Robust topological BIC nanocavities for upconversion directional emission

TL;DR

This paper introduces a topological plasmonic nanocavity design that enables robust, directional, and enhanced single-emitter upconversion emission, overcoming challenges of perturbation and control in nanophotonics.

Contribution

It presents a novel topological cavity architecture that transitions from BICs to multi-BICs, enabling deterministic directional emission and robustness against perturbations.

Findings

Enhanced radiation intensity from single emitters

Uniform and deterministic directional emission achieved

Structural robustness against local perturbations

Abstract

Photonic bound states in the continuum (BICs) provide a revolutionary paradigm for boosting light-matter interactions in integrated nanocavity systems. Nevertheless, precise manipulation of open cavity-emitter architectures still faces critical challenges, especially in realizing deterministic directional radiation and suppressing the perturbation of intrinsic cavity modes induced by emitters as local impurities. Conventional investigations on cavity-emitter coupling are predominantly based on ensemble measurements, which inevitably mask the intrinsic physics underlying individual light-matter interactions. Here, we propose a robust strategy to control the upconversion and emission of a single-particle emitter using a topological plasmonic cavity with broken {\sigma}h mirror symmetry. This structured design enables the transition from symmetry-protected BICs to a multi-BIC regime with finite but ultrahigh confinement, where nontrivial phase evolution and hybridization of transverse electric and magnetic modes open a well-defined far-field radiation channel for directional emission. Leveraging this scheme, we experimentally demonstrate dramatically enhanced radiation intensity from a single point-like emitter, together with uniform and deterministic directional emission, while achieving excellent structural robustness against local perturbations. This work establishes a general framework for engineering coherent directional light emission at the nanoscale, which lays a solid foundation for high-performance chip-scale integrated nanophotonic applications.