# 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.

## Key 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.