Optical metasurfaces are periodic or graded pattern arrays of ultra-thin plasmonic and/or dielectric nanostructures, which are intended to scatter light in manners that cannot be achieved with conventional stratified media. Recent advancements in the theoretical knowledge and fabrication methods of two-dimensional materials, such as graphene, have provided the opportunity to scale down the principles of metasurfaces to atomic dimensions and to offer graded pattern meta-sheets. We present here engineered nanostructures to tailor the beaming pattern of light scattered through such meta-sheets. We obtain designs to precisely control both the in-plane scattering of surface waves associated with the sheets and also out-of-plane scattered far-field beams into a desired direction. We then determine a set of conductivity-balancing conditions to completely confine the surface waves to the meta-sheets at highly scattering sites and demonstrate that under such criterion the propagation of guided surface waves can be described simply using Fresnel equations of plane waves. Furthermore, we cascade three sinusoidally modulated reactance surfaces to realize a broad-beam leaky-wave antenna to completely scatter the surface waves to far-field and also control the steering direction. In addition, conformal patterned 2D sheets will be explored for the first time and how to successfully design and manipulate the light wavefront. For fast and accurate designs of the flat and conformal meta-sheets, we take advantage of our superior auxiliary differential equation finite-difference time-domain (ADE-FDTD) method. Also, an integral equations (IE) model will be applied for large-area system platforms design investigation.
A dual-band multilayer shared aperture antenna (SAA) is presented, which can recognize anomalous two-dimensional beam steering simultaneously at two distinct operating wavelengths lie in near-infrared (NIR) (λ1=1055 nm) and visible (λ2=700 nm) spectra. The supercell consists of one large cross-shaped resonator antenna (top layer) and a 2×2 square-shaped patches (bottom layer). This compact bifunctional dual-band reflectarray SAA can steer the main beam toward relatively large angles (≈40 deg) in both θ- and ϕ-planes at dual-frequency bands. The state-of-the-art techniques in antenna design are exploited to attain the minimized aperture size and negligible coupling among NIR and visible arrays. The overall height of the antenna is 275 nm (≈0.25λ1). The presented structure is customizable in form and can easily be scaled to other frequency ratios.
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.