Dual-Gated Active Metasurface at 1550 nm with Wide (>300°) Phase Tunability

Abstract

Active metasurfaces composed of electrically reconfigurable nanoscale subwavelength antenna arrays can enable real-time control of scattered light amplitude and phase. Achievement of widely tunable phase and amplitude in chip-based active metasurfaces operating at or near 1550 nm wavelength has considerable potential for active beam steering, dynamic hologram rendition, and realization of flat optics with reconfigurable focal lengths. Previously, electrically tunable conducting oxide-based reflectarray metasurfaces have demonstrated dynamic phase control of reflected light with a maximum phase shift of 184° ( Nano Lett. 2016 , 16 , 5319 ). Here, we introduce a dual-gated reflectarray metasurface architecture that enables much wider (>300°) phase tunability. We explore light-matter interactions with dual-gated metasurface elements that incorporate two independent voltage-controlled MOS field effect channels connected in series to form a single metasurface element that enables wider phase tunability. Using indium tin oxide (ITO) as the active metasurface material and a composite hafnia/alumina gate dielectric, we demonstrate a prototype dual-gated metasurface with a continuous phase shift from 0 to 303° and a relative reflectance modulation of 89% under applied voltage bias of 6.5 V.

Phase-only transmissive spatial light modulator based on tunable dielectric metasurface

“…While these are static optical components, for which the phase coverage can be achieved via arranging the constituent nanoantennas with different shapes, sizes, or orientations, for various applications it is also important to find ways to adaptively tune the phase brought to light by the nanoantennas during usage. [25][26][27][28][29][30][31][32][33][34][35] Ultimately, if each single nanoantenna element of a metasurface could be dynamically tuned by applying electrical voltages then it would act as an SLM device with a pixel size smaller than the wavelength of light.…”

Electrically tunable harmonics in time-modulated metasurfaces for wavefront engineering

“…Furthermore, unlike all-optical tunability, electrical tunability easily allows for realization of gradedpatterns through independent biasing of each element without requiring complex lens systems which makes it desirable for wavefront engineering. In particular, graphene and indium tin oxide (ITO) have attracted a lot of attention due to their compatibility with silicon technology, large scale fabrication feasibility and lowdimensionality of the active regions [19,20,24,25]. The carrier concentration in these materials can be tuned through electrostatic gating in parallel capacitor configurations which can be translated into the change in the optical constants of the material through carrier-dependent dispersion models in the infrared (IR) and Terahertz (THz) frequencies.…”

Gate-Tunable Near-Field Heat Transfer

“…The slight increase in integrated heat flux at point A, with respect to bulk SiC, in Fig. 4c, results from the large plasmonic losses (γ p ) in ITO, namely γ ITO = [200 − 263]γ SiC [41,58,59,61,62,66], for the range of carrier densities considered here. The ITO losses result in a slightlybroadened SPhP peak in spectral heat flux (dashed curve in panel (d)) with respect to bulk SiC (black curve in panel (d)), which, when integrated, results in a Q larger than Q SiC .…”

“…In the class of TCOs we investigate ITO, which is traditionally used as a contact electrode in photovoltaic cells due to its simultaneous conducting and transparent nature. ITO is an emerging plasmonic material with considerably lower losses compared to noble metals, while also having gate-tunable carrier density [58,59,[61][62][63][64][65].…”