Abstract
Optical metasurfaces consisting of single-layer nanostructures have immensely promising applications in wavefront control because they can be used to arbitrarily manipulate wave phase, and polarization. However, anomalous refraction and reflection waves have not yet been simultaneously and asymmetrically generated, and the limited efficiency and bandwidth of pre-existing single-layer metasurfaces hinder their practical applications. Here, a few-layer anisotropic metasurface is presented for simultaneously generating high-efficiency broadband asymmetric anomalous refraction and reflection waves. Moreover, the normal transmission and reflection waves are low and the anomalous waves are the predominant ones, which is quite beneficial for practical applications such as beam deflectors. Our work provides an effective method of enhancing the performance of anomalous wave generation, and the asymmetric performance of the proposed metasurface shows endless possibilities in wavefront control for nanophotonics device design and optical communication applications.
Highlights
The phase gradient dφ/dx of the cross polarized wave in Eqs (1) and (2) are opposite for LCP and RCP cross polarized waves with positive and negative signs, respectively. σ =±1 indicating the sign of the phase gradient corresponds to the helicity of left-handed circular polarization (LCP) and right-handed circular polarization (RCP) incident waves propagating along −zdirection
Because arbitrarily polarized incident waves can be decomposed into LCP and RCP components, such waves propagating from the forward or backward direction can simultaneously generate anomalous refraction and reflection waves with same polarization state and the polarization state of generated anomalous waves are orthogonally for these two opposite incident directions, as indicated by Fig. 6(a)
The simulation results are consistent with the theoretical prediction, and high-efficiency broadband asymmetric anomalous refraction and reflection waves are generated
Summary
Previous approaches in few-layer metasurfaces have dramatically enhanced the efficiency of anomalous light, high-efficiency broad-bandwidth anomalous refraction and reflection waves still have not been effectively generated simultaneously. We propose an anisotropic metasurface to simultaneously generate broadband high-efficiency asymmetric anomalous refraction and reflection waves for circularly polarized incident waves in the near-infrared range. Following the approach previously discussed[4], equal polarization conversion amplitudes and the corresponding 2π continuous phase gradient along the direction perpendicular to the wave propagation are necessary for anomalous wave generation. A 0–2π continuous phase gradient of circular polarized conversion waves can be achieved in metasurfaces by rotating the array of the unit-cell structures along the geometric axis parallel to the wave propagation direction from 0 to π. We consider the incoming plane waves propagating along the forward (+z) and backward (−z) directions, with the electric fields as[31,32,33]
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