Controlling nanoscale optical transmission with dielectric metasurfaces at visible wavelengths

Recently, metasurfaces and metalenses have become an important subject in the domain of novel optical devices. Numerous nanostructures, with different fundamental principles, materials, and topologies, have been proposed, but general design rules for optimization of their efficiency are not well established yet. Particularly attractive are metasurfaces consisting of Huygens resonators since they offer precise control of the intensity and phase of the transmitted light. In this paper, we demonstrate a Huygens metasurface capable of focusing visible light. We study the impact of the layout of the lens on their efficiency by comparing two metalenses designs: concentric annular regions of equal width and constant phase, with concentric rings defined by individual nano-resonators. The latter provides a better approximation to the ideal phase profile and as a consequence, a high-efficiency lens. Metalenses with both designs were fabricated by e-beam lithography and characterized with a custom-built setup. Experimental results demonstrate that the design with fine discretization improves the lens efficiency by a factor of 2.6.