Gradient metasurfaces: a review of fundamentals and applications

Abstract

In the wake of intense research on metamaterials the two-dimensional analogue, known as metasurfaces, has attracted progressively increasing attention in recent years due to the ease of fabrication and smaller insertion losses, while enabling an unprecedented control over spatial distributions of transmitted and reflected optical fields. Metasurfaces represent optically thin planar arrays of resonant subwavelength elements that can be arranged in a strictly or quasi periodic fashion, or even in an aperiodic manner, depending on targeted optical wavefronts to be molded with their help. This paper reviews a broad subclass of metasurfaces, viz. gradient metasurfaces, which are devised to exhibit spatially varying optical responses resulting in spatially varying amplitudes, phases and polarizations of scattered fields. Starting with introducing the concept of gradient metasurfaces, we present classification of different metasurfaces from the viewpoint of their responses, differentiating electricaldipole, geometric, reflective and Huygens' metasurfaces. The fundamental building blocks essential for the realization of metasurfaces are then discussed in order to elucidate the underlying physics of various physical realizations of both plasmonic and purely dielectric metasurfaces. We then overview the main applications of gradient metasurfaces, including waveplates, flat lenses, spiral phase plates, broadband absorbers, color printing, holograms, polarimeters and surface wave couplers. The review is terminated with a short section on recently developed nonlinear metasurfaces, followed by the outlook presenting our view on possible future developments and perspectives for future applications.

Ultra-wideband manipulation of electromagnetic waves by bilayer scattering engineered gradient metasurface

“…MLRR provides a new idea for controlling electromagnetic waves, 10,11 where the degree of freedom to control the waves is enhanced by introducing the phase discontinuity over the scale of the wavelength. A smart method to introduce the achromatic phase discontinuity refers to the space-variant PancharatnamBerry (P-B) phase based on the photonic spin-orbit interaction (PSOI).…”

“…7,8 These landmark achievements could open a door for the optical engineering at the subwavelength scale, i.e., for Engineering Optics 2.0, 9 and provide alternatives to traditional approaches based on bulky optical components. [10][11][12][13][14][15][16][17][18] For example, distinct from the electromagnetic absorption in subwavelength structures, 19,20 scattering engineering based on metasurface offer an alternative method for low delectability, [21][22][23][24] which could be considered as a virtual shaping technology. 25 However, most existing metasurfaces suffer from a limited operation bandwidth.…”

Surface Electromagnetic Waves on the Interfaces of Gradient Dielectric Media: Visible Spectral Range

“…Note, that, unlike the traditional model of electromagnetic surface waves on the sharp boundaries of conducting media with free carriers, the phenomena in the gradient non-conducting low loss dielectrics are broadening essentially both the spectral range of surface waves and the list of materials, perspective for creation of new surface waves based devices. [28,39] the computations. All authors contributed to the interpreting the results and writing the manuscript.…”

Fano‐Enhanced Circular Dichroism in Deformable Stereo Metasurfaces

“…2D metasurfaces, endowed with intriguing capabilities for manipulating the behaviors of electromagnetic (EM) waves, represent one of the most striking research topics in photonics areas in the past decade . Compared with 3D optical metamaterials facing enormous challenges in stringent fabrication demands, 2D metasurfaces drastically simplify the fabrication procedures while retaining the exceptional abilities in controlling the propagation properties of optical waves only with deep‐subwavelength thickness .…”