EMET researches from the Universitat Politècnica de València have demonstrated experimentally a multilayer double-negative metamaterial working in the visible range. In collaboration with researchers from the King's College London, our team has built a three-layers fishnet metamaterial that exploits a second-order magnetic resonance to reach the visible regime. The low-loss nature of the employed magnetic resonance, together with the effect of the interacting adjacent layers, results in a figure of merit as high as 3.34. A wide spectral range of negative index is achieved, covering the wavelength region between 620 and 806 nm with only two different designs. This result has been published in Physical Review Letters.
(a) Schematic of a fishnet metamaterial made up of three unit cells in the propagation direction. The overall number of layers is 7 (4 metal layers and 3 dielectric layers).
(b) Top-view SEM image of the fabricated 3-unit-cell fishnet structure 3 (see Table I).
(c) Detail of image in (b).
(d) Detail of the fabricated 3-unit-cell fishnet structure 4.
Moreover, this result has been recognized as a milestone in optical metamaterials in a review written by Costas M. Soukoulis and Martin Wegener which is accepted for publication in Nature Photonics.
 C. García-Meca, J. Hurtado, J. Martí, A.Martínez, W. Dickson and A. V. Zayats “Low-Loss Multilayered Metamaterial Exhibiting a Negative Index of Refraction at Visible Wavelengths”, Physical Review Letters 106, 067402(1)-067402(2) (2011).
Project EMET researchers have developed a novel negative-index metamaterial  based on an array of plasmonic waveguides exhibiting backward modes. The metamaterial is unique in that it uses a fundamentally different approach to the usual resonant-based method of achieving negative index, by using the intrinsic backward properties of plasmonic waveguides which exist under certain conditions. The metamaterial operates throughout a big bandwidth within the visible spectrum, is polarization independent, and is subwavelength in all directions. An extension to 3D is also suggested. Recently, two papers have appeared in Optics Express  and Nature Materials  which confirm the results.
 F. J. Rodríguez-Fortuño, C. García-Meca, R. Ortuño, J. Martí, and A. Martínez, “Coaxial plasmonic waveguide array as a negative-index metamaterial”, Opt. Lett. 34, 3325-3327 (2009)
 René de Waele, Stanley P. Burgos, Harry A. Atwater, and Albert Polman, “Negative refractive index in coaxial plasmon waveguides”, Opt. Express 18, 12770-12778 (2010)
 Stanley P. Burgos, René de Waele, Albert Polman and Harry A. Atwater, “A single-layer wide-angle negative-index metamaterial at visible frequencies”, Nature Materials 9, 407 - 412 (2010)
Project EMET researchers design a metamaterial that could exhibit negative refractive index in the visible spectrum for arbitrary light polarization. This metamaterial is based on a high-order plasmonic resonance present in the so-called fishnet structure and overcomes the challenge of achieving a low-loss polarization-independent medium in the visible spectrum. It could find applications in superlensing and in the fabrication of certain cloaking devices, among other things.
 C. García-Meca, R. Ortuño, F. J. Rodríguez-Fortuño, J. Martí, and A. Martínez, “Double-negative polarization-independent fishnet metamaterial in the visible spectrum”, Optics Letters, Vol. 34, No. 10, pp. 1603-1605 (2009).