Cavity-Enhanced Chiroptical Response in a 2D Visible-Light Plasmonic Metasurface

Achieving strong optical chirality in the visible spectrum remains a central challenge for integrating chiral light–matter interactions into compact photonic platforms. Conventional dielectric chiral structures can produce large circular dichroism (CD) but require thick, high-index geometries that are difficult to fabricate and integrate [1]. Plasmonic metasurfaces, while planar and lithography-compatible, typically show limited chiroptical contrast in the visible range due to radiative losses and weak mode confinement [2]. A two-dimensional chiral microcavity using a chiral organic film has also been reported [3], but its response arises from molecular rather than geometric chirality, limiting field confinement and spectral tunability. We address this challenge by coupling a chiral gold cross-slit nanoarray to a photonic microcavity, forming a composite structure with both resonant frequency selectivity and amplified optical chirality. The resulting visible-range chiral cavity exhibits pronounced CD and helicity-dependent reflection and transmission, significantly exceeding uncoupled metasurfaces. This lithography-based, spectrally tunable architecture provides a route to designing spin-selective photonic devices and strong chiral light–matter coupling.

[1] Zhu, A., Chen, W., Zaidi, A. et al. Light Sci Appl 7, 17158 (2018).

[2] Deng, QM., Li, X., Hu, MX. et al. npj Nanophoton. 1, 20 (2024).

[3] Chen, TL., Salij, A., Parrish, K.A. et al. Nat Commun 15, 3072 (2024).