Focused vortex-beam generation using gap-surface plasmon metasurfaces

In spite of a wide range of applications ranging from particle trapping to optical communication, conventional methods to generate vortex beams suffer from bulky configurations and limited performance. Here, we design, fabricate, and experimentally demonstrate orthogonal linear-polarization conversion and focused vortex-beam generation simultaneously by using gap-surface plasmon metasurfaces that enable high-performance linear-polarization conversion along with the complete phase control over reflected fields, reproducing thereby the combined functionalities of traditional half-wave plates, lenses, and q-plates. The fabricated metasurface sample features the excellent capability of orthogonal linear-polarization conversion and focused vortex-beam generation within the wavelength range of 800-950 nm with an averaged polarization conversion ratio of similar to 80% and absolute focusing efficiency exceeding 27% under normal illumination with the x-polarized beam. We further show that this approach can be extended to realize a dual-focal metasurface with distinctly engineered intensity profiles by using segmented metasurfaces, where an orthogonal-polarized beam with Gaussian-distributed intensity and a vortex beam with intensity singularity have been experimentally implemented. The proposed multifunctional metasurfaces pave the way for advanced research and applications targeting photonics integration of diversified functionalities.