Chiral Quasi-Bound States in the Continuum

TL;DR

This paper demonstrates that chiral perturbations enable quasi-bound states in the continuum (q-BICs) to operate with arbitrary elliptical polarizations, leading to highly efficient wavefront shaping and spectral filtering in metasurfaces.

Contribution

It introduces a novel approach using geometric phase engineering to extend q-BICs to elliptical polarizations, enhancing metasurface functionalities.

Findings

Achieved ultrasharp Fano spectral features in metasurfaces.

Enabled near-unity efficiency in wavefront shaping.

Demonstrated precise spectral filtering capabilities.

Abstract

Quasi-bound states in the continuum (q-BICs) are resonant states of suitably tailored nanostructures with long optical lifetimes controlled by symmetry-breaking perturbations. While in planarized ultrathin devices the resulting Fano resonance is limited to linear polarizations, we show here that chiral perturbations extend q-BIC concepts to arbitrary elliptical polarizations. Using geometric phase engineering, we realize metasurfaces with ultrasharp Fano spectral features that can shape the impinging wavefront with near-unity efficiency, while at the same time precisely filtering their spectral content.