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It is found that there exist composite media that exhibit strong spatial dispersion even in the very large wavelength limit. This follows from the study of lattices of ideally conducting parallel thin wires ͑wire media͒. In fact, our analysis reveals that the description of this medium by means of a local dispersive uniaxial dielectric tensor is not complete, leading to unphysical results for the propagation of electromagnetic waves at any frequencies. Since nonlocal constitutive relations have been usually considered in the past as a secondorder approximation, meaningful in the short-wavelength limit, the aforementioned result presents a relevant theoretical interest. In addition, since such wire media have been recently used as a constituent of some discrete artificial media ͑or metamaterials͒, the reported results open the question of the relevance of the spatial dispersion in the characterization of these artificial media. Causality imposes that all material media must be dispersive. In most cases this behavior results in local dispersive constitutive relations, i.e., in frequency-dependent constitutive permittivity and permeability tensors. Nonlocal dispersive behavior ͑i.e., spatial dispersion͒, which results in constitutive operators depending also on the spatial derivatives of the mean fields ͑or, for plane electromagnetic waves, on the wave-vector components͒, is usually considered as a small effect, meaningful in the short-wavelength limit. Specifically, spatial dispersion will always appear when the higher-order terms in the series expansion of the constitutive parameters in power series of the dimensionless parameter a/ (a is the lattice constant of the crystal and the wavelength inside the medium͒ are not neglected.

Original realization of a lens capable to transmit images with sub-wavelength resolution is proposed. The lens is formed by parallel conducting wires and effectively operates as a telegraph: it captures image at the front interface and the transmit it to the back interface without distortion. This regime of operation is called canalization and is inherent in flat lenses formed by electromagnetic crystals. The theoretical estimations are supported by numerical simulations and experimental verification. Sub-wavelength resolution of λ/15 and 18% bandwidth of operation are demonstrated at gigahertz frequencies. The proposed lens is capable to transport sub-wavelength images without distortion to nearly unlimited distances since the influence of losses to the lens operation is negligibly small.

The physics and applications of a broad class of artificial electromagnetic materials composed of lattices of aligned metal rods embedded in a dielectric matrix are reviewed. Such structures are here termed wire metamaterials. They appear in various settings and can operate from microwaves to THz and optical frequencies. An important group of these metamaterials is a wire medium possessing extreme optical anisotropy. The study of wire metamaterials has a long history, however, most of their important and useful properties have been revealed and understood only recently, especially in the THz and optical frequency ranges where the wire media correspond to the lattices of microwires and nanowires, respectively. Another group of wire metamaterials are arrays and lattices of nanorods of noble metals whose unusual properties are driven by plasmonic resonances.

Imaging with sub-wavelength resolution using a lens formed by periodic metal-dielectric layered structure is demonstrated. The lens operates in canalization regime as a transmission device and it does not involve negative refraction and amplification of evanescent modes. The thickness of the lens have to be an integer number of half-wavelengths and can be made as large as required for ceratin applications, in contrast to the other sub-wavelength lenses formed by metallic slabs which have to be much smaller than the wavelength. Resolution of λ/20 at 600 nm wavelength is confirmed by numerical simulation for a 300 nm thick structure formed by a periodic stack of 10 nm layers of glass with ǫ = 2 and 5 nm layers of metal-dielectric composite with ǫ = −1. Resolution of λ/60 is predicted for a structure with same thickness, period and operating frequency, but formed by 7.76 nm layers of silicon with ε = 15 and 7.24 nm layers of silver with ε = −14.PACS numbers: 78.20. Ci, 42.30.Wb,41.20.Jb The possibility of imaging with sub-wavelength resolution was first reported by Pendry in 2000 [1]. It was shown that the slab of left-handed material [2], a medium with both negative permittivity and permeability, can create images with nearly unlimited resolution. This idea impeached validity of classical restriction on resolution of imaging systems: diffraction limit and became a starting point for creation of new research area of metamaterials [3], artificial media possessing extraordinary electromagnetic properties usually not available in the natural materials. The idea of Pendry's perfect lens is based on such exotic phenomena observable in left-handed media as backward waves, negative refraction and amplification of evanescent waves. The far-field of a source is focused due to effects of backward waves and negative refraction. The near field of the source, which contains sub-wavelength details, is recovered in the image plane because of the amplification of evanescent modes in the slab. Currently, the samples of left-handed materials are created only in microwave region [4]. The creation of lefthanded materials at THz frequencies and in optical range meets with problems related to the difficulty in getting required magnetic properties [5,6] which have to be created artificially. In the absence of magnetic properties the lenses formed by materials with negative permittivity only (for example, silver at optical frequencies) are still capable to create images with sub-wavelength resolution, but the operation is restricted to p-polarization only and the lens has to be thin as compared to the wavelength [1]. This idea was confirmed by recent experimental results [7] which demonstrated the reality of sub-wavelength imaging using silver slabs in optical frequency range. The resolution of such lenses is restricted by losses in the silver, but this problem can be alleviated by cutting the slab into the multiple thin layers [8,9] and introduction of active materials [10]. Unfortunately, at the moment there is no recipe how to incre...

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We demonstrate that an array of metallic nanorods enables sub-wavelength (near-field) imaging at infrared frequencies. Using an homogenization approach, it is theoretically proved that under certain conditions the incoming radiation can be transmitted by the array of nanorods over a significant distance with fairly low attenuation. The propagation mechanism does not involve a resonance of material parameters and thus the resolution is not strongly affected by material losses and has wide bandwidth. The sub-wavelength imaging with λ/10 resolution by silver rods at 30 THz is demonstrated numerically using full-wave electromagnetic simulator.