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

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.