Vortex beam generation using all dielectric metasurface

Abstract

Refractive and conventional optical elements such as prisms and lenses are heavy, large-sized and have limited performance in light-material interactions. Due to these severe constraints, new types of structures called metasurfaces, which are composed of subwavelength structural elements with subwavelength thicknesses, are used instead of conventional and refractive based optical elements. Metasurfaces enable unprecedented control of phase, polarization, amplitude and impedance of incident light. Thanks to these very effective features, metasurfaces have gathered remarkable attention in wavefront manipulation of photons for various applications. Earlier attempts have deployed plasmonic metasurfaces in the designs. However, the light coupled to plasmons suffers from great optical loss, which restricts high transmission efficiency, at visible wavelengths due to intrinsic heat dissipation. This problem can be overcome using all dielectric structures operating mainly in the transmission mode. Here, we numerically demonstrate vortex beam generation having donut-like intensity profile and 60% transmission efficiency. In this study, we use all dielectric metasurface that is composed of thick glass substrate and crystalline silicon which is shaped as trapezoid structure at 532 nm visible wavelength. The refractive indices of glass substrate and crystalline silicon are 1.46 and 4.15 with height of 220 nm, respectively at the designed wavelength. We have achieved 0-2? phase distribution by scaling trapezoid shaped silicon at fixed height. The interface of metasurface segmented 8 regions is filled with trapezoid shaped silicon with a ?/4 phase increment in an azimuthal pattern. The obtained vortex beam can be used in various applications such as light trapping, optical tweezers, and laser beam forming. © 2018 SPIE.