Electrically Tunable Metamaterials Based on Multimaterial Nanowires Incorporating Transparent Conductive Oxides

Salary, Mohammad Mahdi; Mosallaei, Hossein

doi:10.1038/s41598-017-09523-4

Cited by 34 publications

(35 citation statements)

References 63 publications

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“…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.…”

Section: Introductionmentioning

confidence: 99%

Electrically tunable harmonics in time-modulated metasurfaces for wavefront engineering

2018

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Modulation of metasurfaces in time gives rise to several exotic space-time scattering phenomena by breaking the reciprocity constraint and generation of higher-order frequency harmonics. We introduce a new design paradigm for time-modulated metasurfaces, enabling tunable engineering of the generated frequency harmonics and their emerging wavefronts by electrically controlling the phase delay in modulation. It is demonstrated that the light acquires a dispersionless phase shift regardless of incident angle and polarization, upon undergoing frequency conversion in a timemodulated metasurface which is linearly proportional to the modulation phase delay and the order of generated frequency harmonic. The conversion efficiency to the frequency harmonics is independent of modulation phase delay and only depends on the modulation depth and resonant characteristics of the metasurface, with the highest efficiency occurring in the vicinity of resonance, and decreasing away from the resonant regime. The modulation-induced phase shift allows for creating tunable spatially varying phase discontinuities with 2π span in the wavefronts of generated frequency harmonics for a wide range of frequencies and incident angles. Specifically, we apply this approach to a time-modulated metasurface in the Teraherz regime consisted of graphene-wrapped silicon microwires. For this purpose, we use an accurate and efficient semi-analytical framework based on multipole scattering. We demonstrate the utility of the design rule for tunable beam steering and focusing of generated frequency harmonics giving rise to several intriguing effects such as spatial decomposition of harmonics, anomalous bending with full coverage of angles and dual-polarity lensing. Furthermore, we investigate the angular and spectral performance of the time-modulated metasurface in manipulation of generated frequency harmonics to verify its constant phase response versus incident wavelength and angle. The nonreciprocal response of the metasurface in wavefront engineering is also studied by establishing nonreciprocal links with large isolations via modulationinduced phase shift. The proposed design approach enables a new class of high-efficiency tunable metasurfaces with wide angular and frequency bandwidth, wavefront engineering capabilities, nonreciprocal response and multi-functionality.

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Section: Introductionmentioning

confidence: 99%

Electrically tunable harmonics in time-modulated metasurfaces for wavefront engineering

2018

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“…In this manuscript, n‐type silicon with the doping concentration of 5 × 10 16 cm −3 is assumed. It has been observed that applying different voltages directly to silicon will negligibly modify its optical characteristics like dissipative loss and frequency dispersion of dielectric constant . As shown in Figure e, an electrical bias can be applied across the top Si‐made nanodisk and the bottom gold back mirror.…”

Section: Resultsmentioning

confidence: 99%

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

Forouzmand

Salary

Inampudi

et al. 2018

Advanced Optical Materials

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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.

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“…4. The procedure for obtaining scattered fields in an aperiodic array is similar with the governing matrix equation being replaced with (19) and the scattered field being given by (15). Further details regarding technical implementation and assembling of matrices are given in the Supplemental Material 54 .…”

Section: E Scope Of the Methodsmentioning

confidence: 99%

“…In conventional designs of metamaterials, the gradient characteristics are achieved through geometrical variation of building blocks which makes their operation static, tying them to a specific application after fabrication. More recently, several efforts have been put into post-fabrication control of the metamaterials by exploiting mechanical reconfiguration 8,9 , thermal phase transitions 10,11 and electro-optical materials [12][13][14][15][16][17] in geometrically fixed platforms. Such tunable designs render more flexibility in the operation allowing for multifunctionality and on-demand manipulation of light.…”

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confidence: 99%

Time-varying metamaterials based on graphene-wrapped microwires: Modeling and potential applications

2018

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Electrically Tunable Metamaterials Based on Multimaterial Nanowires Incorporating Transparent Conductive Oxides

Cited by 34 publications

References 63 publications

Electrically tunable harmonics in time-modulated metasurfaces for wavefront engineering

Electrically tunable harmonics in time-modulated metasurfaces for wavefront engineering

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

Time-varying metamaterials based on graphene-wrapped microwires: Modeling and potential applications

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