A Tunable Multigate Indium-Tin-Oxide-Assisted All-Dielectric Metasurface

In this paper, an optically active reflective metasurface with tunable phase performance is designed which operates based on the excitation of both electric and magnetic resonances in a silicon-made nanoantenna element and the use of layered indium tin oxide (ITO)-alumina under the influence of external multigate biasing. The capability of achieving robust control over the reflection characteristics of two closely spaced electric and magnetic resonances is investigated. Adopting the multigate biasing enables relatively high reflection amplitude of 0.4 over the entire phase-change coverage (approximate to 180 degrees) in the near-infrared regime by exploiting the constructive interference between the geometrical resonances. The physical mechanism behind this ITO-assisted metal-insulator-semiconductor building block can be described as the strong confinement of electromagnetic fields at the vicinity of ITO layers and the possibility of modulating the carrier concentrations of the integrated active materials by electrically varying the bias voltage. The uniformity of reflection magnitude for all reflection phase coverage, relatively high reflectivity, and electro-optical tunability is leveraged to design three multifunctional devices with step-by-step increase in complexity of biasing network including ultrathin reconfigurable linear/circular polarizer (simple identical biasing), dynamical beam steering platform (two-state biasing), and tunable metalens with controllable on- and off-axes focusing pattern in real-time (advanced element-by-element biasing).