Quantification of the Transmission Properties of Anisotropic Metasurfaces Illuminated by Finite-Size Beams

The aim of this paper is to present an analytical method to quantitatively address the influence of a focusing illumination on the optical response properties of a metasurface illuminated by a finite-size beam. Most theoretical and numerical studies are performed by considering an infinite periodic structure illuminated by a plane wave. In practice, one deals with a finite-size illumination and structure. The combination of the angular spectrum expansion with a monomodal modal method is used to determine the beam size needed to acquire efficient properties of a metasurface that behaves as an anisotropic plate. Interesting results show that the beam-size can be as small as 5 x 5 periods to recover the results of a plane wave. Other results also show that the beam-size can be used as an extrinsic parameter to enhance the anisotropic metasurface performance and to adjust its expected properties finely (birefringence and/or transmission coefficient). These findings are important for the design of real (finite) structures and can be adapted for experimental conditions to achieve optimized results and take full advantage of the metamaterial properties.