Ultra-thin, planar, Babinet-inverted plasmonic metalenses

Abstract

We experimentally demonstrate the focusing of visible light with ultra-thin, planar metasurfaces made of concentrically perforated, 30-nm-thick gold films. The perforated nano-voids-Babinet-inverted (complementary) nano-antennas-create discrete phase shifts and form a desired wavefront of cross-polarized, scattered light. The signal-to-noise ratio in our complementary nano-antenna design is at least one order of magnitude higher than in previous metallic nano-antenna designs. We first study our proof-of-concept 'metalens' with extremely strong focusing ability: focusing at a distance of only 2.5 mm is achieved experimentally with a 4-mm-diameter lens for light at a wavelength of 676 nm. We then extend our work with one of these 'metalenses' and achieve a wavelength-controllable focal length. Optical characterization of the lens confirms that switching the incident wavelength from 676 to 476 nm changes the focal length from 7 to 10 mm, which opens up new opportunities for tuning and spatially separating light at different wavelengths within small, micrometer-scale areas. All the proposed designs can be embedded on-chip or at the end of an optical fiber. The designs also all work for two orthogonal, linear polarizations of incident light.

Light concentration using hetero-junctions of anisotropic low permittivity metamaterials

“…This result even significantly outperforms (by an order of magnitude) the recently demonstrated extreme short focusing using transmitarrays of optical antennas, 39,40 which reported a best case of f/D50.625 (2.5 mm/4 mm) at l 0 5676 nm. 40 There are several parameters that determine the operation of the device, primarily the effective permittivity z' , x' f g, the tilt angle a and the thickness. These parameters determine the location of the focal spot with respect to the exit facet as well as the strength of the focus.…”

“…It is shown that such a device can in fact outperform thick lenses with very low f/D ratios, to create areas of high power concentration very close to the exit facet of the device, i.e., at short focal distances. It also outperforms the recently reported flat and thin lenses realized using arrays of optical antennas 39,40 in terms of their f/D ratios. The proposed focusing hetero-junction device is an alternative method for extremely close power concentration under normal incidence.…”

“…Light concentration using hetero-junctions of anisotropic low permittivity metamaterials M Memarian and GV Eleftheriades 7 order of several wavelengths. 40 The f/D ratio for the range of devices in Figure 6a is 0.02-0.2, for instance, f/D50.075 for the l 0 thick case. Figure 6b shows a half-wavelength thick lossy focusing device realized with Ag/glass, which is still able to achieve concentration at a distance of about l 0 /4.…”

Microwave Tunable Metasurfaces Implemented With Ferroelectric Materials and Periodical Copper Wires

“…Metasurfaces have also been proposed to implement metalenses working in different bands [7][8][9][10]. Near-infrared metalenses and axicons have been proposed at λ ∼ 1.5 µm [7,8] and 1 THz [10].…”

“…Metasurfaces comprised of nanoantenna phased-array have been investigated for holography, quarter-waveplate, metalenses, and meta-mirrors [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17].…”