Pairing Toroidal and Magnetic Dipole Resonances in Elliptic Dielectric Rod Metasurfaces for Reconfigurable Wavefront Manipulation in Reflection

Abstract

A novel approach for reconfigurable wavefront manipulation with gradient metasurfaces based on permittivity‐modulated elliptic dielectric rods is proposed. It is shown that the required 2π phase span in the local electromagnetic response of the metasurface can be achieved by pairing the lowest magnetic dipole Mie resonance with a toroidal dipole Mie resonance, instead of using the lowest two Mie resonances corresponding to fundamental electric and magnetic dipole resonances as customarily exercised. This approach allows for the precise matching of both the resonance frequencies and quality factors. Moreover, the accurate matching is preserved if the rod permittivity is varied, allowing for constructing reconfigurable gradient metasurfaces by locally modulating the permittivity in each rod. Highly efficient tunable beam steering and beam focusing with ultrashort focal lengths are numerically demonstrated, highlighting the advantage of the low‐profile metasurfaces over bulky conventional lenses. Notably, despite using a matched pair of Mie resonances, the presence of an electric polarizability background allows to perform the wavefront shaping operations in reflection, rather than transmission. This has the advantage that any control circuitry necessary in an experimental realization can be accommodated behind the metasurface without affecting the electromagnetic response.

Error Analysis of Programmable Metasurfaces for Beam Steering

“…Metasurfaces are structures generally composed of an array of subwavelength resonators referred to as unit cells. The characteristics of these building blocks determine the metasurface response, this is, its absorption, reflection, and transmission characteristic [4], [39], [40].…”

On the calculation of the quality factor in contemporary photonic resonant structures

“…(13). The dielectric meta-atom examined in this section is commonly used as the fundamental unit cell for realizing all-dielectric metasurfaces, capable of purposefully manipulating light [40]. The correct estimation of the Q-factor in this case is equally important.…”

Toroidal Dipole Resonances in All‐Dielectric Oligomer Metasurfaces

“…[25][26][27] Nevertheless, after accounting for the feasibility of fabrication and optical measurements in realistic scenarios, we suggest that the frontal excitation utilized here might be more compatible with experimental designs and potential applications. Metamolecules (unit cells) are arranged periodically in xand ydirection with equal periodicity P, forming infinitely large metasurfaces in the xy-plane.…”