https://doi.org/10.1140/epjd/s10053-026-01158-3
Research - Photon
Chiral quasi-bound states in the continuum for third harmonic generation with giant chirality
School of Mathematical and Physical Sciences, Dalian Polytechnic University, Dalian, People’s Republic of China
a
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Received:
4
December
2025
Accepted:
31
March
2026
Published online:
15
April
2026
Abstract
In this work, we propose and numerically investigate a chiral dielectric metasurface composed of asymmetric N-shaped silicon resonators that support symmetry-protected bound states in the continuum (BICs). By breaking in-plane symmetry via a tunable geometric parameter (ΔL = a − b), the ideal BIC transforms into a quasi-BIC with a high Q-factor and strong circular dichroism (CD) reaching 0.91. Multipole decomposition reveals the quasi-BIC is driven primarily by the interplay of electric dipole, magnetic dipole, and magnetic quadrupole moments. The structure exhibits exceptional chirality-dependent response, enabling selective excitation of the high-Q quasi-BIC only under left-handed circular polarization (LCP), which leads to a significant enhancement of the local electric field (over 2000). This chiral field confinement is leveraged for efficient third-harmonic generation (THG), achieving a high efficiency of 0.812 × 10⁻2% under LCP excitation and a large nonlinear chiral dichroism (THG-CD) of up to 1.81. The metasurface demonstrates simultaneous handedness preservation and polarization extinction in linear operations, offering a powerful platform for advanced chiral nanophotonics, including spin-selective nonlinear optics and polarization-encoded devices.
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© The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature 2026
Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
