Intrinsic chirality of dielectric metasurfaces unlocked by resonant chiral modes

TL;DR

This paper experimentally demonstrates that bilayer dielectric metasurfaces can exhibit strong optical chirality through resonant chiral modes, enabled by symmetry breaking and interlayer coupling, without intrinsically chiral components.

Contribution

It confirms the theoretical prediction that bilayer metasurfaces with rotated apertures can produce pronounced chiral responses via resonant modes, expanding the design toolkit for chiroptical nanophotonics.

Findings

Resonant circular dichroism observed in silicon membrane metasurfaces.

Symmetry breaking with a thin PMMA layer activates chiral response.

Chiral response governed by interlayer coupling and mode properties.

Abstract

Controlling optical chirality at the subwavelength scales is essential for many applications of nanophotonic structures in polarization optics, sensing, and nonlinear photonics. Achieving a strong chiroptical response in planar dielectric metasurfaces without intrinsically chiral building blocks (or "meta-atoms") remains challenging. The recent theoretical study [ACS Photonics 12, 6717 (2025)] predicted that bilayer metasurfaces with rotated C$_4$-symmetric apertures can exhibit pronounced chiral response originating from resonant chiral photonic modes realizing maximum chirality under the mode strong coupling. That observation uncovers a novel mechanism of metasurface chirality. Here, we confirm experimentally this novel concept and demonstrate resonantly enhanced circular dichroism in the near-infrared frequency range. We fabricate a free-standing silicon membrane metasurface that is nominally achiral. When out-of-plane symmetry is broken by a thin PMMA layer, it unlocks and activates a strong chiral response. The observed circular dichroism is explained by the properties of chiral photonic modes, and it is governed by interlayer coupling and symmetry breaking, in agreement with theoretical predictions. These results establish bilayer metasurfaces as a simple and versatile platform for engineering strong mode-induced chirality in compact planar photonic metadevices.