Broadband reflective lens in visible band based on aluminum plasmonic metasurface

We demonstrate a flat optical lens based on plasmonic reflectarray metasurface, which consists of a planar array of hyperbolic-shaped aluminum (Al) nanoantenna separated from an Al ground plane by a SiO2 spacer. The gradual change in the width of the Al nanoantenna enables unique broadband (400-700 nm) to focus on the visible band because of its hyperbolic reflection-phase profile. The focal length of metalens is quickly decreased with the increase of wavelength in the short wavelength region (400-550 nm), compensating the chromatic aberration in traditional lenses. In long wavelength region (550-700 mn), the focal length has only a slight change, thereby minimizing chromatic aberration. Funhermore, the proposed metalens creates a small focal spot beyond diffraction limit, while maintaining high focusing efficiency. Our method of simple and anisotropic nanoantenna is used to realize wide phase tuning range offers a novel strategy to design braodband metalens, and our inetalens has widespread applications in compact camera, telescope, and microscope. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement