Abstract
Luneburg lenses and Maxwell fisheye lenses possess distinct properties of focusing, well beyond conventional lenses made of uniform materials. In this paper, a planar broadband bifunctional Luneburg-fisheye lens synthesized by gradient anisotropic metasurface is proposed. The proposed anisotropic metasurface is formed by non-resonant anisotropic cells, so that it can independently realize the equivalent gradient refractive indexes of Luneburg lens and Maxwell fisheye lens along orthogonal directions in a broad band, respectively. To verify the performance of the bifunctional lens, a prototype associated with a feeding log-periodic dipole antenna has been fabricated. Experimental results show that the proposed lens functions well over a wide frequency range with high efficiency and low profile, which coincides well with theoretical predictions and simulated results. It is expected that the proposed design will facilitate the applications of multifunctional metadevices in microwave and optical ranges.
Highlights
Among the gradient refractive index (GRIN) lenses, Luneburg lens and Maxwell Fisheye lens have come into prominence recently and become more and more indispensable in collimating lights, wide-angle cameras, and communication systems due to their distinct properties of focusing[21]
Despite the ease of fabrication and superior performance, most of the Luneburg lenses or Maxwell fisheye lenses designed previously by metamaterials still suffer from bulk configurations[22–26]
We will discuss the feasibility of realizing a Luneburg-fisheye lens with anisotropic metasurface (AM)
Summary
Metasurfaces, by virtue of their fantastic physical characteristics associated with ultrathin configurations, have attracted an extensive interest in the fields of microwave, optics, and even a coustics[1–3]. As alternatives to conventional lenses, gradient refractive index (GRIN) lenses constructed by inhomogeneous artificially structured metasurfaces can achieve significant reductions in volume and weight, facilitating the integration with other microwave or optical d evices[15]. Maxwell Fisheye lens is a spherically symmetric GRIN lens as well, whose refractive index decreases radially from 2 at the center to 1 on the perimeter in general. It can focus the radiation emitted from a point source to a diametrically opposite point on the lens rim. Most of the flat metalenses in contemporary works could hardly adjust the distributions of the refractive index along two polarization directions independently[27–32], namely that most of them are isotropic and serving as single-function devices. Lenses mentioned above are extremely restricted because of the intrinsic resonance characteristics of the AMs and the coupling between adjacent cells
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