Gate-Tunable Conducting Oxide Metasurfaces

TLDR

Metasurfaces composed of subwavelength planar arrays can manipulate light extraordinarily, enabling ultrathin optical components, yet their post‑fabrication tunability of reflected or transmitted amplitude and phase remains limited. This work experimentally demonstrates a gate‑tunable metasurface that allows dynamic electrical control of the reflected wave’s phase and amplitude. Tunability is achieved by field‑effect modulation of the complex refractive index of conducting‑oxide layers incorporated into reflectarray antenna elements. The device delivers a 180° phase shift and ~30% reflectance change at 2.5 V, supports modulation above 10 MHz, and switches ±1‑order diffracted beams, paving the way for reconfigurable ultrathin optical components such as beam‑steering devices and dynamic holograms.

Abstract

Metasurfaces composed of planar arrays of subwavelength artificial structures show promise for extraordinary light manipulation. They have yielded novel ultrathin optical components such as flat lenses, wave plates, holographic surfaces, and orbital angular momentum manipulation and detection over a broad range of the electromagnetic spectrum. However, the optical properties of metasurfaces developed to date do not allow for versatile tunability of reflected or transmitted wave amplitude and phase after their fabrication, thus limiting their use in a wide range of applications. Here, we experimentally demonstrate a gate-tunable metasurface that enables dynamic electrical control of the phase and amplitude of the plane wave reflected from the metasurface. Tunability arises from field-effect modulation of the complex refractive index of conducting oxide layers incorporated into metasurface antenna elements which are configured in reflectarray geometry. We measure a phase shift of 180° and ∼30% change in the reflectance by applying 2.5 V gate bias. Additionally, we demonstrate modulation at frequencies exceeding 10 MHz and electrical switching of ±1 order diffracted beams by electrical control over subgroups of metasurface elements, a basic requirement for electrically tunable beam-steering phased array metasurfaces. In principle, electrically gated phase and amplitude control allows for electrical addressability of individual metasurface elements and opens the path to applications in ultrathin optical components for imaging and sensing technologies, such as reconfigurable beam steering devices, dynamic holograms, tunable ultrathin lenses, nanoprojectors, and nanoscale spatial light modulators.