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An ultrathin single-layer metasurface manifesting both linear cross-polarization conversion (CPC) and linear-to-circular polarization (LP-to-CP) conversion in X-band is presented in this research. The designed metasurface acts as a multifunctional metasurface achieving CPC over a fractional bandwidth of 31.6% (8–11 GHz) with more than 95% efficiency while linear-to-circular polarization conversion is realized over two frequency bands from 7.5–7.7 GHz and 11.5–11.9 GHz. Moreover, the overall optimized structure of the unit cell results in a stable polarization transformation against changes in the incidence angle up to 45° both for transverse-electric (TE) and transverse-magnetic (TM) polarizations. The proposed metasurface with simple structure, compact size, angular stability and multifunctional capability qualifies for many applications in communication and polarization manipulating devices.

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A broadband microwave cross-polarization-conversion (CPC) metasurface is designed, simulated, fabricated, and tested. The metasurface consists of coupled split-ring-resonators (SRRs) with two splits in each SRR and is designed on an FR4 dielectric substrate backed by a metallic ground plane. An efficient CPC, both for normal as well as for oblique incidence, is achieved with 3 dB fractional bandwidth of 73% from 5 to 10.8 GHz. This wideband polarization conversion results from multiple plasmonic resonances occurring at three neighboring frequencies. Owing to the sub-wavelength unit cell size and symmetric structure of the coupled SRRs, the response of the metasurface is independent of the polarization and incidence angle of the incoming wave, which makes it a potential candidate for many practical applications. The proposed design is validated both numerically and experimentally. Experimental results are found to be in good agreement with simulations.

Metasurfaces, two dimensional (2D) metamaterials comprised of subwavelength features, can be used to tailor the amplitude, phase and polarisation of an incident electromagnetic wave propagating at an interface. Though many novel metasurfaces have been explored, the hunt for cost-effective, highly efficient, low-loss and polarisation insensitive applications is ongoing. In this work, we utilise an efficient and cost-effective dielectric material, hydrogenated amorphous silicon (a-Si:H), to create a ultra-thin transmissive surface that simultaneously controls phase. This material exhibits significantly lower absorption in the visible regime compared to standard amorphous silicon, making it an ideal candidate for various on-chip applications. Our proposed design, which works on the principle of index waveguiding, integrates two distinct phase profiles, that of a lens and of a helical beam, and is versatile due to its polarisation-insensitivity. We show how this metasurface can lead to highly concentrated optical vortices in the visible domain, whose focused ring-shaped profiles carry orbital angular momentum at the miniaturised scale.