Visible-frequency metasurfaces for broadband anomalous reflection and   high-efficiency spectrum splitting
  Ultrathin metasurfaces have recently emerged as promising materials to enable novel, flat optical components and surface-confined, miniature photonic devices. However, experimental realization of high-performance metasurfaces at visible frequencies has been a significant challenge due to high plasmonic losses and difficulties in high-uniformity nanofabrication. Here, we propose a highly-efficient yet simple metasurface design comprising of single gradient antenna as unit cell. We demonstrate visible broadband (450 - 850 nm) anomalous reflection and spectrum splitting with 85% conversion efficiency. Average power ratio of anomalous reflection to the strongest diffraction was calculated to be ~ 103 and measured to be ~ 10. The anomalous reflected photons and spectrum splitting performance have been visualized using CCD and characterized using angle-resolved measurement setup. Metasurface design proposed here is a clear departure from conventional metasurfaces utilizing multiple, anisotropic resonators, and could enable high-efficiency, broadband metasurfaces for achieving directional emitters, polarization/spectrum splitting surfaces for spectroscopy and photovoltaics. 
Zhongyang Li, Edgar Palacios, Serkan Butun and Koray Aydin
cond-mat.mes-hall physics.optics