Ali Forouzmand

Tunable two dimensional optical beam steering with reconfigurable indium tin oxide plasmonic reflectarray metasurface

In this paper, an electrically tunable reflectarray metasurface for two dimensional (2D) beam steering is designed by integration of a thin layer of indium tin oxide (ITO) material into a metal-insulator-metal (MIM) plasmonic unit-cell. The reflectarray is composed of square-shaped patch nanoantennas placed on a stack of insulator-ITO-metallic ground plane. The resonant characteristic of unit-cell and the accumulation of carrier density at the interface of ITO-insulator play key roles in obtaining over 250° of phase agility at around 218 terahertz (THz), by electrically varying the bias voltage. An array of unit-cells with integrated ITO and 2D voltage biasing distribution (from the side) offer the possibility of designing a reconfigurable antenna in which the main beam can be steered to relatively large angles in both θ- and - planes at carefully selected operating frequency. The significant advantage of this design is the dynamically adjustable radiation pattern in both azimuth and elevation planes even after fabrication.

Real-Time Controllable and Multifunctional Metasurfaces Utilizing Indium Tin Oxide Materials: A Phased Array Perspective

In this paper, two electrically tunable dual-band reflectarray antennas are designed by the integration of a thin layer of indium tin oxide (ITO) into plasmonic multi-sized and multilayer unit cells. The presented geometries include two gold nanoribbons located next to each other with different widths and backed by a stack of alumina-ITO-metallic ground plane and two pairs of vertically stacked gold nanoribbon-alumina-ITO on a metallic ground plane. The double-resonance nature of the double metal-insulator-metal unit-cells is exploited to achieve two distinct operating frequencies in which the control over phase of the reflected beam is obtained via the tunable gate biasing of ITO. An in-depth phased array analysis is developed with emphasis on the accomplishment of a reconfigurable antenna with robust beam scanning and focusing characteristics. The proposed structures can be considered as dual-band bifunctional reflectarray antenna that can operate at two distinct frequencies in the near-infrared regime with two different functionalities as bending and focusing.

Manipulation of surface plasmon polariton propagation on isotropic and anisotropic two-dimensional materials coupled to boron nitride heterostructures

We present a comprehensive analysis of surface plasmonpolaritondispersioncharacteristics associated with isotropic and anisotropic two-dimensional atomically thin layered materials (2D sheets) coupled to h-BN heterostructures. A scattering matrix based approach is presented to compute the electromagnetic fields and related dispersioncharacteristics of stacked layered systems composed of anisotropic 2D sheets and uniaxial bulk materials. We analyze specifically the surface plasmonpolariton (SPP) dispersioncharacteristics in case of isolated and coupled two-dimensional layers with isotropic and anisotropic conductivities. An analysis based on residue theorem is utilized to identify optimum optical parameters (surface conductivity) and geometrical parameters (separation between layers) to maximize the SPP field at a given position. The effect of type and degree of anisotropy on the shapes of iso-frequency curves and propagation characteristics is discussed in detail. The analysis presented in this paper gives an insight to identify optimum setup to enhance the SPP field at a given position and in a given direction on the surface of two-dimensional materials.

A functional metasurface platform with unique building blocks: light manipulation and beam shaping

This paper presents an engineered metasurface which can serve functionalities such as anomalous bending, focusing, and beam shaping over the circularly polarized (CP) incident beam. The building block is a bilayer double split-loop resonators (DSLRs) where it can fully transmit the impinging light and control phase only by rotation of unit-cell and not by changing the structural parameters which can greatly facilitate the fabrication process. The mechanism behind this fascinating feature can be described as the conversion of an impinging CP incident beam into the opposite handedness and obtaining a geometrical phase shift equal to twice the rotating angle of DSLRs. It is illustrated that full transmission with 2π phase shift can be achieved with the proposed metasurface. Unique designs with helicity dependency to realize anomalous bending, bifunctional convergence/divergence, and flat-top beam creation with applying lossless beam shaping approach are presented.

Excitation of Discrete and Continuous Spectrum in Subdiffraction Wire-Medium Type Lenses

Subwavelength imaging of the near field of a magnetic line-source excitation is studied for several wire-medium (WM) lens topologies using complex-plane analysis of the radiation integral. Nonlocal homogenization is used for the wire medium, resulting in an analytical expression for the transfer function of the lens. It is shown that by evaluating the Sommerfeld integral of the transmitted field in terms of the discrete and continuous spectra provides a general framework for better understanding of electromagnetic phenomena involved with subwavelength imaging. Results are obtained for a WM slab, and for a wire medium loaded with graphene monolayers and periodic arrays of graphene patches, demonstrating the interplay of the discrete and continuous spectral components in different operating regimes of the lenses. The imaging with a stack of silver slabs is also considered for comparison purposes.

Multifunctional metasurfaces nanoantennas by gate-tunable materials

Here, advanced approaches based on the concept of gate-tunable materials are presented in order to implement and design novel real-time controllable and multifunctional metasurfaces of nanoantennas. A tunable dual-band bifunctional (bending/focusing) reflectarray antenna is implemented by the integration of a thin layer of indium tin oxide (ITO) into plasmonic double metal/insulator/metal nanoribbons (bi-MIM) unit-cells. The double-resonance nature of the unit-cell is employed to attain two distinct operating frequencies wherein the robust control over the phase of the reflected beam is achieved by the tunable gate biasing of ITO. The design is carried out based on the phased array principle and the desired phase profiles for bending and focusing are realized by proper tuning of one-dimensional (1D) biasing network. The plasmonic-based design suffers from the inherent high-level losses which degrade the reflection efficiency. To overcome this vulnerable imperfection, an electrically controlled all-dielectric nanostructured metasurface loaded with gate-tunable material is proposed which operates based on dielectric-type Mie resonance and can drastically improve the reflection performance.