Label-free plasmonic biosensors rely either on surface plasmon polaritons or on localized surface plasmons on continuous or nanostructured noble-metal surfaces to detect molecular-binding events. Despite undisputed advantages, including spectral tunability, strong enhancement of the local electric field and much better adaptability to modern nanobiotechnology architectures, localized plasmons demonstrate orders of magnitude lower sensitivity compared with their guided counterparts. Here, we demonstrate an improvement in biosensing technology using a plasmonic metamaterial that is capable of supporting a guided mode in a porous nanorod layer. Benefiting from a substantial overlap between the probing field and the active biological substance incorporated between the nanorods and a strong plasmon-mediated energy confinement inside the layer, this metamaterial provides an enhanced sensitivity to refractive-index variations of the medium between the rods (more than 30,000 nm per refractive-index unit). We demonstrate the feasibility of our approach using a standard streptavidin-biotin affinity model and record considerable improvement in the detection limit of small analytes compared with conventional label-free plasmonic devices.

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.

All-optical signal processing enables modulation and transmission speeds not achievable using electronics alone. However, its practical applications are limited by the inherently weak nonlinear effects that govern photon-photon interactions in conventional materials, particularly at high switching rates. Here, we show that the recently discovered nonlocal optical behaviour of plasmonic nanorod metamaterials enables an enhanced, ultrafast, nonlinear optical response. We observe a large (80%) change of transmission through a subwavelength thick slab of metamaterial subjected to a low control light fluence of 7 mJ cm(-2), with switching frequencies in the terahertz range. We show that both the response time and the nonlinearity can be engineered by appropriate design of the metamaterial nanostructure. The use of nonlocality to enhance the nonlinear optical response of metamaterials, demonstrated here in plasmonic nanorod composites, could lead to ultrafast, low-power all-optical information processing in subwavelength-scale devices.

We analyze the optical properties of plasmonic nanorod metamaterials in the epsilon-near-zero regime and show, both theoretically and experimentally, that the performance of these composites is strongly affected by nonlocal response of the effective permittivity tensor. We provide the evidence of interference between main and additional waves propagating in the room-temperature nanorod metamaterials and develop an analytical description of this phenomenon. Additional waves are present in the majority of low-loss epsilon-near-zero structures and should be explicitly considered when designing applications of epsilon-near-zero composites, as they represent a separate communication channel.

Hyperbolic materials enable numerous surprising applications that include far-field subwavelength imaging, nanolithography, and emission engineering. The wavevector of a plane wave in these media follows the surface of a hyperboloid in contrast to an ellipsoid for conventional anisotropic dielectric. The consequences of hyperbolic dispersion were first studied in the 50's pertaining to the problems of electromagnetic wave propagation in the Earth's ionosphere and in the stratified artificial materials of transmission lines. Recent years have brought explosive growth in optics and photonics of hyperbolic media based on metamaterials across the optical spectrum. Here we summarize earlier theories in the Clemmow's prescription for transformation of the electromagnetic field in hyperbolic media and provide a review of recent developments in this active research area. "Far-field imaging device: planar hyperlens with magnification using multi-layer metamaterial," Opt. Express 16(25), 21142-21148 (2008). 18. Y. Xiong, Z. Liu, and X. Zhang, "A simple design of flat hyperlens for lithography and imaging with half-pitch resolution down to 20 nm," Appl. Phys. Lett. 94(20), 203108 (2009). 19. S. Thongrattanasiri and V. A. Podolskiy, "Hypergratings: nanophotonics in planar anisotropic metamaterials,"Opt. Lett. 34(7), 890-892 (2009). 20. L. Verslegers, P. B. Catrysse, Z. Yu, and S. Fan, "Deep-subwavelength focusing and steering of light in an aperiodic metallic waveguide array," Phys. using a hyperbolic medium with a single slit," Appl. Opt. 50(31), G27-G30 (2011). 24. S. Ishii, A. V. Kildishev, E. Narimanov, V. Shalaev, and V. P. Drachev, "Sub-wavelength interference pattern from volume plasmon polaritons in a hyperbolic medium," Laser Photonics Rev. 7(2), 265-271 (2013). 25. J. Kim, V. P. Drachev, Z. Jacob, G. V. Naik, A. Boltasseva, E. E. Narimanov, and V. M. Shalaev, "Improving the radiative decay rate for dye molecules with hyperbolic metamaterials," Opt. Express 20(7), 8100-8116 (2012). 26. G. V. Naik, J. Liu, A. V. Kildishev, V. M. Shalaev, and A. Boltasseva, "Demonstration of Al:ZnO as a plasmonic component for near-infrared metamaterials," "Negative refraction in semiconductor metamaterials," Nat. Mater. 6(12), 946-950 (2007). 28.

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We have observed laserlike emission of surface plasmon polaritons (SPPs) decoupled to the glass prism in an attenuated total reflection setup. SPPs were excited by optically pumped molecules in a polymeric film deposited on the top of a silver film. Stimulated emission was characterized by a distinct threshold in the input-output dependence and narrowing of the emission spectrum. The observed stimulated emission and corresponding compensation of the metallic absorption loss by gain enables many applications of metamaterials and nanoplasmonic devices.

We study perspectives of nanowire metamaterials for negative-refraction waveguides, highperformance polarizers, and polarization-sensitive biosensors. We demonstrate that the behavior of these composites is strongly influenced by the concentration, distribution, and geometry of the nanowires, derive an analytical description of electromagnetism in anisotropic nanowire-based metamaterials, and explore the limitations of our approach via three-dimensional numerical simulations. Finally, we illustrate the developed approach on the examples of nanowire-based high energy-density waveguides and non-magnetic negative index imaging systems with far-field resolution of one-sixth of vacuum wavelength.The anisotropy of effective dielectric permittivity is widely used in optical, infrared (IR), THz and GHz sensing, spectroscopy, and microscopy 1,2,3,4 . Strongly anisotropic optical materials can be utilized in nonmagnetic, non-resonant optical media with negative index of refraction, and have the potential to perform subdiffraction imaging and to compress the radiation to subwavelength areas 2,5,6,7 . The performance of these polarization-sensitive applications can be related to the relative difference of the dielectric constant along the different directions. In the majority of natural anisotropic crystals this parameter is below 30% 8 . While it may be sufficient for some applications, a number of exciting phenomena ranging from high-performance polarization control 4 to subwavelength light guiding 2,5,6 to planar imaging 7 require different components of a permittivity tensor to be of different signs.In this Letter we study the perspectives of using nanowire composites as meta-materials with extreme optical anisotropy. We demonstrate that even 10% stretching/compression of the nanowire structures may dramatically affect the electromagnetic properties of these systems and change the sign of components of the permittivity tensor. We present an analytical description of wave propagation in anisotropic nanowire composites -Generalized Maxwell-Garnett approach (GMG), and verify our technique via three-dimensional (3D) numerical simulations. Finally, we illustrate our approach on the examples of several nanowire-based systems for light compression below the diffraction limit and negative refractionimaging with far-field resolution of λ 0 /6 (with λ 0 being free-space wavelength).The use of metallic wire mesh as anisotropic lowfrequency plasma has been proposed in 9 and experimentally realized for normal light incidence in 4,10 . However, the applicability of these nanowire-based materials for any non-trivial geometry involving oblique light incidence or wave-guiding is still considered to be questionable due to strong nonlocal interactions 11 , that may potentially result in positive components of the permittivity tensor. Furthermore, the majority of existing effective-medium theories (EMTs) 11,12,13,14 are limited to the optical response of nanowires that are isotropically distributed in the host material. The predicted respo...