Strong Mode Coupling via Quasi-Bound States in the Continuum in Bianisotropic Metasurfaces

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Main Authors: Máñez-Espina, Luis Manuel, Amrahi, Bahman, Asadchy, Viktar, Díaz-Rubio, Ana
Format: Preprint
Published: 2025
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author Máñez-Espina, Luis Manuel
Amrahi, Bahman
Asadchy, Viktar
Díaz-Rubio, Ana
author_facet Máñez-Espina, Luis Manuel
Amrahi, Bahman
Asadchy, Viktar
Díaz-Rubio, Ana
contents Electromagnetic mode coupling plays a key role in many resonant effects in nanophotonics. This coupling is also responsible for the appearance of bianisotropy, where electric and magnetic responses become interconnected through the interaction of their respective modes. In this work, we develop a simple and general temporal coupled-mode theory model to describe off-diagonal chiral bianisotropy. Using quasi-bound states in the continuum (q-BICs), we demonstrate how to control the hybridization of modes with opposite symmetries, resulting in Rabi-like splitting between the hybrid states in the regime of strong electromagnetic mode coupling. Beyond revealing the physical origin of the hybrid modes, our model predicts and explains the emergence of dual-band asymmetric reflection and absorption, and how to achieve maximum directional absorption difference. The theoretical predictions are verified by full-wave simulations, showing very good agreement with theory. Furthermore, very strong reciprocal bianisotropy is demonstrated with the use of q-BICs in a deeply subwavelength metasurface in the optical frequency range. Our results provide a clear physical picture of the interaction process between modes, offering a compact theoretical framework for understanding and designing bianisotropic dielectric metasurfaces not only in the traditional regime but also in the strong coupling regime.
format Preprint
id arxiv_https___arxiv_org_abs_2512_08927
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Strong Mode Coupling via Quasi-Bound States in the Continuum in Bianisotropic Metasurfaces
Máñez-Espina, Luis Manuel
Amrahi, Bahman
Asadchy, Viktar
Díaz-Rubio, Ana
Optics
Electromagnetic mode coupling plays a key role in many resonant effects in nanophotonics. This coupling is also responsible for the appearance of bianisotropy, where electric and magnetic responses become interconnected through the interaction of their respective modes. In this work, we develop a simple and general temporal coupled-mode theory model to describe off-diagonal chiral bianisotropy. Using quasi-bound states in the continuum (q-BICs), we demonstrate how to control the hybridization of modes with opposite symmetries, resulting in Rabi-like splitting between the hybrid states in the regime of strong electromagnetic mode coupling. Beyond revealing the physical origin of the hybrid modes, our model predicts and explains the emergence of dual-band asymmetric reflection and absorption, and how to achieve maximum directional absorption difference. The theoretical predictions are verified by full-wave simulations, showing very good agreement with theory. Furthermore, very strong reciprocal bianisotropy is demonstrated with the use of q-BICs in a deeply subwavelength metasurface in the optical frequency range. Our results provide a clear physical picture of the interaction process between modes, offering a compact theoretical framework for understanding and designing bianisotropic dielectric metasurfaces not only in the traditional regime but also in the strong coupling regime.
title Strong Mode Coupling via Quasi-Bound States in the Continuum in Bianisotropic Metasurfaces
topic Optics
url https://arxiv.org/abs/2512.08927