A compact polarization insensitive all-dielectric metasurface lens for Gaussian to tophat beam shaping in sub-terahertz regime

Abstract

In this paper, we present a Gaussian to tophat beam shaper (GTBS) based on an all-dielectric metasurface lens for sub terahertz (sub-THz) applications. In order to calculate the required phase profile of the GTBS, we use an analytical procedure based on the geometrical transformation technique. The calculated phase profile is then realized by a silicon (Si) metasurface lens consisting of rectangular-shaped pillars of subwavelength dimensions. Because of large solution domain relative to the operation wavelength, we combined the beam envelope and the finite element methods to simulate the structure with a high precision. By designing an anti-reflection metasurface made up of periodically arranged Si pillars of subwavelength dimensions at the back surface of the beam shaper, we reduced the reflection from the lens surface considerably. The proposed idea is firstly investigated in a two-dimensional (2D) structure composed of an array grooves in a Si substrate and then is extended to three dimensions (3D) by considering a 2D array of subwavelength pillars or holes. The 3D structure is shown to be polarization insensitive. The compactness, ease of fabrication, low transmission loss, polarization independence, and straightforward design of the proposed metasurface beam shaper lens make it a promising choice for the implementation of sub-THz quasi-optical elements especially for standoff imaging systems.