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

Abstract

distribution and adaptive beamforming. Toward the realization of these active engineered structures various mechanisms have been utilized including mechanical reconfiguration, [4,5] photoswitching of dye molecules, [6] nonlinear optical effects, [7] thermal phase transitions, [8,9] and electrooptical field-effect modulation. [10][11][12][13][14][15][16][17][18] Among the aforementioned techniques, electro-optical controllable devices offer continuous tunability, shorter response time, and relatively wide tuning range comparing to thermal and mechanical tunable stimulations. Furthermore, the possibility of direct and independent electrical biasing of each inclusion within an optical platform makes this approach more favorable than all-optical tunability approaches. [19,20] Wide range of electrooptical materials have recently emerged like graphene, liquid crystals, [11] doped semiconductors (InSb and GaAs), [12,13] and transparent conducting oxides materials (TCOs) [14,15] including indium tin oxide (ITO), doped zinc oxide (ZnO), and aluminum-, gallium-, and indium-doped zinc-oxide (AZO, GZO, and IZO). In the mid-infrared and far-infrared spectra, the surface conductivity of graphene is widely tunable by the change of its electrochemical potential via applying an external gate voltage. Due to the extreme thinness, conformable to diverse patterning schemes, and broadband operation, it has been exploited in reconfigurable metadevices for manipulation of the surface plasmons and dynamical tuning of the geometrical resonances. [16][17][18] In the near-infrared (NIR) regime, TCOs are of particular interest due to the short response time (≈ns), fabrication feasibility, the controllable optical and electrical properties through the pre-and post-depositional processes, and large variation of complex refractive index (unity-order index change) in the charge accumulation/depletion regime. Also, the epsilon-near-zero (ENZ) property has been observed at the NIR regime and telecommunication frequency range when the carrier concentration of TCO is in the range of 10 20 -10 21 cm −3 . [21][22][23][24] ITO as the most well-known TCO has been exploited in the design of various optoelectronic devices. [25][26][27][28][29][30][31][32][33][34][35] Due to the fact that the ultrathin active layer of ITO has limited interaction length with the normal impinging wave, two approaches have been proposed to overcome the weak interaction between light and ITO. First, integration of ITO into a subwavelength grating A. Forouzmand, M. M. Salary, Dr.

Electrically tunable harmonics in time-modulated metasurfaces for wavefront engineering

“…However, the change in the carrier concentration is limited to a thin accumulation layer for ITO and to a two-dimensional surface for graphene. Due to this fact, these materials have been incorporated in resonant geometries which can enhance the light-matter interaction in the active regions and enable tunable modulation of phase over a wide range in reflection [19,20,[24][25][26][27] or transmission [28] through spectral shift of the resonance. Despite the fruitful progress that has been made toward electrically tunable modulation of light wavefront, all the proposed designs thus far suffer from a limited efficiency as they cannot cover the entire 2π span for phase modulation.…”

Tunable Metasurfaces Based on Active Materials

“…Therefore, the modulation depth could be limited. This problem can potentially be relieved through dual or even multiple gates, which can achieve phase tuning greater than 300° . Optical pump can be another solution to increase the modulation depth.…”

“…This problem can potentially be relieved through dual or even multiple gates, which can achieve phase tuning greater than 300°. [70,74] Optical pump can be another solution to increase the modulation depth. An ultrafast plasmonic modulator based on an ITO nanorod array is reported by Guo et al, whose structure is displayed in Figure 4d.…”

Progresses in the practical metasurface for holography and lens

“…In the case of the metaholograms so far, the phase mask recorded in the metasurface cannot be changed into other information once it has been fabricated. To address these limitations, some of the recent published studies have proposed dynamic metaholograms using various methods [60,[80][81][82][83]. When a meta-atom is designed using a material whose permittivity changes by external bias, the metasurface can contain more than one information without change of incident light properties.…”