Nanohole-based phase gradient metasurfaces for light manipulation

The commonly accepted approach for metasurface design utilizes nanopillars with varying diameters. In this study, contrary to usual design approach, we propose and design highly efficient, broadband and polarization-independent nanohole all-dielectric metasurfaces operating in the visible spectrum. High focusing efficiency above 70% is achieved between 450 and 700 nm wavelength region with a numerical aperture (NA) value of 0.60. Moreover, focusing efficiency is succeeded higher than 47% with NA  =  0.85 for a design wavelength of 532 nm. Nanohole metasurfaces exhibit less chromatic aberration (<18%) compared to nanopillar based metasurfaces. The nanohole array metasurfaces is investigated under the oblique illumination condition and its performance is found to be satisfactory in a wide range of incidence angles. Furthermore, nanohole and nanopillar metasurfaces are analyzed and their performances are compared for different incidence angles, NAs and operating wavelengths. It is shown that contrary to dielectric pillars commonly deployed in the design of metasurfaces, nanoholes with varying diameters allow phase changes with better performances. (paper)