Twisted-Nematic Liquid Crystal-Infiltrated Bilayer Metasurface for Circular-Polarization LCoS Devices

TL;DR

This paper introduces a new metasurface device that enables electrically tunable circular polarization for use in advanced optical applications.

Contribution

The integration of a twisted nematic liquid crystal with a bilayer metasurface enables tunable circular dichroism for CP LCoS devices.

Findings

The device achieved an experimentally measured CD switching of 8.2% at 1550 nm.

Numerical simulations predicted a maximum CD of 0.47 at 1575 nm.

Lateral misalignment between metasurface layers was identified as the main cause of performance discrepancy.

Abstract

Optical chirality underpins applications ranging from
molecular
identification to facial recognition. Metasurfaces have recently emerged
as a versatile platform for compact chiral photonic devices. Here,
we demonstrate electrically tunable circular dichroism (CD) at telecommunication
wavelengths using a bilayer metasurface integrated with a twisted
nematic liquid crystal (TN LC). The device comprises two silicon cuboid
metasurface layers rotated by 30° relative to each other, with
the interlayer gap filled by TN LC. The LC alignment was experimentally
verified, confirming an effective metasurface-induced director orientation.
Numerical simulations predict a maximum CD of 0.47 at 1575 nm, while
experiments reveal an electrically tunable CD switching (ΔCD)
of 8.2% at 1550 nm. This discrepancy is primarily attributed to lateral
misalignment between the bilayer metasurfaces, as confirmed by numerical
simulations. This architecture provides a practical route to extend
conventional liquid crystal on silicon (LCoS) devices, typically designed
for linearly polarized (LP) light, toward circular polarization-based
LCoS (CP LCoS) devices, enabling opportunities for applications such
as biomedical imaging and smart glasses.

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