Highly Efficient Bifunctional Dielectric Metasurfaces at Visible Wavelength: Beam Focusing and Anomalous Refraction in High-Order Modes

Zhenyu Xu,Zhiwei Li,Yunbing Wei,Yanqing Tian,Fei Wu

doi:10.3389/fphy.2020.575824

Zhenyu Xu, Zhiwei Li + Show 3 more

Open Access

https://doi.org/10.3389/fphy.2020.575824

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Abstract

Metasurface is an artificially arranged sub-wavelength micro-structure array. Each structure can be regarded as an unit cell controlled by electromagnetic wave. Recently, bifunctional metasurfaces have aroused increasing interest and become excellent candidates for device miniaturization and integration. In this paper, we propose a highly efficient bifunctional metasurface, composed of silicon nanopillars, enabling anomalous beam deflection and focusing at visible wavelength. Based on the designed metasurface, the other two metasurfaces are presented successfully, demonstrating high-order anomalous beam deflection and focusing. This work will establish a positive prospect for the development of high-performance bifunctional metasurface.

Highlights

The complete control of electromagnetic waves has always been an emerging field of research
The meta-atom constituting the metasurface unit cell is made of rectangular silicon nanopillar, enduing polarization-selective phase shifts to realize the two functions. With regard to this purpose, we first discussed the relationship between the geometric parameters of the nanopillar and the polarization-dependent phase shifts, the results show that, upon the light with the designated polarizations in normal incidence, the metasurface exhibits a highly efficient and ignorable functional crosstalk beam anomalous refraction, and exhibits light focusing
For the proposed dielectric metasurface, it is believed that the Si nanopillar constituting the unit cell plays a role as a truncated waveguide and operates as a low-quality factor Fabry-Pérot resonance [20]

Summary

Introduction

The complete control of electromagnetic waves has always been an emerging field of research. Considering the fact that the conventional optical components rely on gradual phase shifts accumulated during light propagation to shape light beams [1], a three-dimensional metamaterial, exhibits peculiar material properties that do not exist in nature, provide a more flexible way in manipulating the wavefront of electromagnetic waves, which can be used to realize negative refractive index [2], perfect lens [3], and invisibility cloaking [4]. Three-dimensional metamaterials have many drawbacks, such as high inherent losses and manufacturing difficulties, which limit the miniaturization of the device in practice. With the development of nanotechnology, a metasurface, which is regarded as a two-dimensional metamaterial, has been proposed to cope with the drawbacks due to its ultrathin sub-wavelength structure, relatively easy to manufacture and conformal integration with systems [5, 6]. Based on the obvious features, various metasurfaces with different functions have been extensively studied, including beam deflectors [7,8,9,10], metalenses [11,12,13], waveplates [14, 15], and high-resolution holograms [16, 17]

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