title: Graded metascreens to enable a new degree of nanoscale light management.
abstract: Optical metasurfaces, typically referred to as two-dimensional metamaterials, are arrays of engineered subwavelength inclusions suitably designed to tailor the light properties, including amplitude, phase and polarization state, over deeply subwavelength scales. By exploiting anomalous localized interactions of surface elements with optical waves, metasurfaces can go beyond the functionalities offered by conventional diffractive optical gratings. The innate simplicity of implementation and the distinct underlying physics of their wave-matter interaction distinguish metasurfaces from three-dimensional metamaterials and provide a valuable means of moulding optical waves in the desired manner. Here, we introduce a general approach based on the electromagnetic equivalence principle to develop and synthesize graded, non-periodic metasurfaces to generate arbitrarily prescribed distributions of electromagnetic waves. Graded metasurfaces are realized with a single layer of spatially modulated, electrically polarizable nanoparticles, tailoring the scattering response of the surface with nanoscale resolutions. We discuss promising applications based on the proposed local wave management technique, including the design of ultrathin optical carpet cloaks, alignment-free polarization beam splitters and a novel approach to enable broadband light absorption enhancement in thin-film solar cells. This concept opens up a practical route towards efficient planarized optical structures with potential impact on the integrated nanophotonic technology.
authors.affiliation: Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78712, USA.
authors.forename: Nasim
authors.identifier: http://orcid.org/0000-0002-5408-4110
authors.initials: N
authors.lastname: Mohammadi Estakhri
authors.affiliation: Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588, USA.
authors.forename: Christos
authors.identifier: http://orcid.org/0000-0002-8481-8648
authors.initials: C
authors.lastname: Argyropoulos
authors.affiliation: Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78712, USA alu@mail.utexas.edu.
authors.forename: Andrea
authors.identifier: http://orcid.org/0000-0002-4297-5274
authors.initials: A
authors.lastname: Alù
keywords: cloaking; equivalence principle; integrated photonics; metamaterials and metasurfaces; plasmonics; wavefront shaping