Super-resolution imaging using a three-dimensional metamaterials nanolens

Abstract

Super-resolution imaging beyond Abbe's diffraction limit can be achieved by utilizing an optical medium or "metamaterial" that can either amplify or transport the decaying near-field evanescent waves that carry subwavelength features of objects. Earlier approaches at optical frequencies mostly utilized the amplification of evanescent waves in thin metallic films or metal-dielectric multilayers, but were restricted to very small thicknesses ͑Ӷ , wavelength͒ and accordingly short object-image distances, due to losses in the material. Here, we present an experimental demonstration of super-resolution imaging by a low-loss three-dimensional metamaterial nanolens consisting of aligned gold nanowires embedded in a porous alumina matrix. This composite medium possesses strongly anisotropic optical properties with negative permittivity in the nanowire axis direction, which enables the transport of both far-field and near-field components with low-loss over significant distances ͑Ͼ6 ͒, and over a broad spectral range. We demonstrate the imaging of large objects, having subwavelength features, with a resolution of at least / 4 at near-infrared wavelengths. The results are in good agreement with a theoretical model of wave propagation in anisotropic media.

Hyperlenses and metalenses for far-field super-resolution imaging

“…Experimental demonstrations, however, were limited to subwavelength imaging in the near field using metallic wires grown in dielectric templates 45,46 . The tapered nanorod array with a magnification mechanism for far-field imaging still suffers critical challenges in achieving accurate growth at tapered angles and introducing gaps between the arrays 47 .…”

Past achievements and future challenges in the development of three-dimensional photonic metamaterials

“…22,24,28,[30][31][32] , (b) "stereo-" or chiral metamaterials (see also Fig. 3) via stacked electron-beam lithography 12,[35][36][37][38][39][44][45] , (c) chiral metamaterials made via direct-laser writing and electroplating 46 , (d) hyperbolic (or indefinite) metamaterial 51,[53][54][55][56][57][58] that can be made by electroplating of hexagonal-hole-array templates 57 , (e) metaldielectric layered metamaterial composed of coupled plasmonic waveguides enabling angle-independent negative refraction for particular frequencies 52,53 , (f) split-ring resonators oriented in all three dimensions accessible via membrane projection lithography 59 , (g) wide-angle visible negative-index metamaterial based on a coaxial design 97 , (h) blueprint for a connected cubic-symmetry negative-index metamaterial structure amenable to direct laser writing 60 , (i) blueprint for a metal cluster-of-clusters visible-frequency magnetic metamaterial amenable to large-area selfassembly 61 , and (j) blueprint for an all-dielectric negative-index metamaterial composed of two sets of high-refractiveindex dielectric spheres arranged on a simple-cubic lattice [62][63][64][65]75 .…”

“…The notion "hyperbolic metamaterial" stems from the resulting hyperbolic shape of the iso-frequency surfaces in wave-vector space 51 . These anisotropic systems can be used to achieve broadband all-angle negative refraction and super lens imaging [51][52][53][54][55][56][57][58] , for example. Corresponding experiments (negative refraction and subwavelength imaging) have been published at microwave 54 , infrared 52,55 , and visible wavelengths 57 .…”

3D THz metamaterials from micro/nanomanufacturing

“…An array of aligned gold nanowires embedded in a porous alumina matrix was used for the fabrication of superlenses [48]. Such porous alumina matrices can be obtained by anodizing of aluminium.…”

“…Process materials like substrates, resists, and sputter targets should be readily available. State-of-the-art experimental devices were made primarily from -primary pattern generation including direct writing by means of electron, laser, and ion beams [13,41] -UV or X-ray lithography (LIGA) [11,13,15,16,19] -Nanoimprint lithography [50] -Interferometric lithography enhanced by other process steps [14,51] -direct laser writing exploiting two-photon-absorption in resist [44][45][46] -directional evaporation and deposition [47] -electroplating in porous alumina templates [48] -self-rolling of strained layers [52]. Furthermore, Moser et al proposed plastic molding of metamaterials, in particular, of the meta-foil [53].…”