What question did this study set out to answer?

The research aims to investigate the properties of a chiral metasurface that exhibits circular dichroism in the visible spectrum.

April 4, 2026Optical Review0 citationsOpen Access

Broadband reflective circular dichroism in the visible-light region from an aluminum chiral metasurface fabricated with a lift-off-free double-layer structure

AMAtsushi MotogaitoMie University RFRyune FukushiMie University YTYoshio TakeshimaYamaguchi University

Key Points

The research aims to investigate the properties of a chiral metasurface that exhibits circular dichroism in the visible spectrum.
Utilized experimental and numerical approaches to analyze an aluminum chiral metasurface.
Fabricated a Z-shaped unit cell on fused silica with a lift-off-free double-layer structure.
Performed rigorous coupled-wave analysis to evaluate reflectances under circularly polarized light.
Achieved a maximum RCD of ~ 0.12 within the visible spectrum (≈480–630 nm).
Demonstrated consistent peak positions in measured spectra.
Identified design factors impacting performance, including resist thickness and aluminum coverage.

Abstract

We experimentally and numerically investigate an aluminum (Al) chiral metasurface exhibiting broadband reflective circular dichroism (RCD) in the visible. The metasurface comprises a Z-shaped unit cell patterned in electron-beam resist on fused silica and covered with thermally evaporated Al. A lift-off-free “double-layer” Al/resist architecture is formed in a single deposition, consisting of (i) Al on the resist surface and (ii) Al at the aperture bottoms, separated by the resist. Rigorous coupled-wave analysis (RCWA) reproduces the measured co- and cross-polarized reflectances under right- and left-circularly polarized illumination and clarifies parameter dependences. The simulated RCD, defined as the difference between cross-polarized reflectances for the two circular polarizations, exceeds 0.2 over a visible band (≈480–630 nm). The measured spectra show consistent peak positions, with a maximum RCD of ~ 0.12 and values ≥ 0.05 across ~ 508–640 nm. The remaining simulation–experiment gap is likely influenced by uncertainties in thickness, particularly the postexposure/development resist thickness (estimated to decrease from ~ 100 nm to ~ 50–60 nm), as well as metallization-related factors such as the effective Al coverage/thickness. Electromagnetic-field analysis indicates polarization-dependent localization: edge-localized plasmons enhance the magnetic response and cross-polarized reflection for one handedness, whereas field confinement inside the recesses increases absorption and suppresses the cross-polarized response of the opposite handedness. Because the structure is implemented without multilayer alignment and relies on a single metal deposition, it provides a fabrication-friendly route to visible-band chiroptical devices. This lithography-compatible, visible-band platform is promising for polarization control and chiroptical sensing, including compact components compatible with white-light illumination.

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