Design and Experimental Validation of a Flexible and Optically Transparent Metasurface for Broadband Linear-to-Circular Polarization Conversion

The potential use of transparent metasurfaces in an optical system has driven significant research interest in recent years. However, issues such as insufficient flexibility and bandwidth have limited its real-world implementation. This study introduces a flexible and optically transparent metasurface (FAOTM), which is designed and characterized to efficiently convert linear polarization (LP) incident waves to circular polarization (CP) reflected waves across a broad spectrum of frequencies. The meta-atom of a FAOTM consists of an indium-tin-oxide (ITO) based diagonal butterfly-shaped pattern on top of polydimethylsiloxane (PDMS) dielectric substrate along with polyethylene-terephthalate (PET) supportive layer. Within the frequency range of 18.4 to 25.0 GHz for x- and y-polarizations, the numerical analysis demonstrates that the axial ratio (AR) is less than 3-dB, which corresponds to a fractional bandwidth (FBW) of 30%. The bandwidth for linear-to-circular polarization (LTCP) conversion is maintained across the specified frequency range at an oblique incidence angle of 30°. Additionally, to offer a deeper understanding of the polarization conversion mechanism, a comprehensive analysis is conducted through a combination of theoretical analysis, surface current distribution, and equivalent circuit modeling. Finally, a prototype with 25 × 25 units is fabricated and experimental test is carried out. The experimental results exhibited good agreement with the simulation outcomes, confirming the performance of the proposed design.