We propose an approach to far-field optical imaging beyond the diffraction limit. The proposed system allows image magnification, is robust with respect to material losses and can be fabricated by adapting existing metamaterial technologies in a cylindrical geometry.

An optical metamaterial is a composite in which subwavelength features, rather than the constituent materials, control the macroscopic electromagnetic properties of the material. Recently, properly designed metamaterials have garnered much interest because of their unusual interaction with electromagnetic waves. Whereas nature seems to have limits on the type of materials that exist, newly invented metamaterials are not bound by such constraints. These newly accessible electromagnetic properties make these materials an excellent platform for demonstrating unusual optical phenomena and unique applications such as subwavelength imaging and planar lens design. 'Negative-index materials', as first proposed, required the permittivity, epsilon, and permeability, mu, to be simultaneously less than zero, but such materials face limitations. Here, we demonstrate a comparatively low-loss, three-dimensional, all-semiconductor metamaterial that exhibits negative refraction for all incidence angles in the long-wave infrared region and requires only an anisotropic dielectric function with a single resonance. Using reflection and transmission measurements and a comprehensive model of the material, we demonstrate that our material exhibits negative refraction. This is furthermore confirmed through a straightforward beam optics experiment. This work will influence future metamaterial designs and their incorporation into optical semiconductor devices.

We propose a system for far field optical imaging below the diffraction limit. As opposed to the "superlens" based on negative index materials, our approach allows image magnification and is robust with respect to material losses.OCIS codes: (110.0180) Microscopy; (160.1190) Anisotropic optical materials Diffraction limit of conventional optics prevents subwavelength spatial features of the object from contributing to a far field image. Such fine details are encoded in rapid spatial variations of electromagnetic fields which decay exponentially with distance and are thus only detectable in the near field via, e.g., near field scanning optical microscopy [1]. While successful in resolving subwavelength structures, this technique suffers from several drawbacks, including low throughput, the necessity for substantial post-processing of the scanning probe data, and inability to simultaneously observe different parts of the imaged object [1]. It is therefore highly desirable for many applications (e.g. biological microscopy) to use a system which would produce a direct optical far field image that includes subwavelength details.It is for this reason that the recently proposed "superlens" [2] (a device capable of subwavelength resolution that relies on materials with negative index of refraction [3]) received much attention [2][3][4][5][6]. However, subsequent studies demonstrated that subwavelength resolving power of most superlens implementations is severely curtailed by losses [6] or by the characteristic patterning scale of the negative index system. Furthermore, although a superlens amplifies evanescent modes, they still decay exponentially with distance away from the device. Finally, the planar structure of the system limits optical magnification to unity.Here we propose a device capable of forming a magnified optical image of a subwavelength object in the far field. The output of the system consists entirely of propagating waves, which can be processed by conventional optics. Furthermore, our simulations show that material losses do not appreciably degrade the performance of the proposed device.Our approach is based on metamaterials with strong dielectric anisotropy [7] which enable efficient coupling to evanescent fields [8]. If the dielectric constants in the two perpendicular directions are of opposite signs (which can be achieved e.g. in a system of interleaved metallic (ε < 0) and dielectric (ε > 0) layers [9]), the dispersion law for the corresponding bulk TM waves takes the hyperbolic form, , | | 2 2 2 || || 2 c k k ω ε ε = − ⊥ ⊥(1) Fig. 1 (a): Dispersion law for a conventional anisotropic material with ε || , ε ⊥ > 0 (blue curve) and for a material with ε || > 0, ε ⊥ < 0 (red curve); (b) a whispering gallery mode in a cylinder made of a regular dielectric; (c) a whispering gallery mode in a cylinder made of ε || > 0, ε ⊥ < 0 metamaterial (see also Fig. 2a) a2049_1.pdfQTuD3.pdf ©OSA 1-55752-834-9

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We describe a unique class of metamaterials that exhibit strong uniaxial anisotropy with epsilon-zero response along the optical axis and which optical properties depend strongly on polarization. In an example of array of silver nanowires grown in anodic alumina membrane, the proposed singular uniaxial metamaterial is shown to function as a polarizer and narrowband angular transmittance filter.