Man-made Media Research Articles

Hyperbolic metamaterials: production, properties, applications, and prospects

Manmade media (MMMs) consisting of uniaxial photonic crystals with inserts of layers (films) or cylinders embedded in a periodic way into a dielectric substrate with dielectric permeability (DP) are considered. Approximate model-based and accurate electrodynamic methods for describing such MMMs, which are referred to in the case of metal (conductive) or ferrite (metaatom) inserts as a ‘hyperbolic metamaterial’ (HMM), are analyzed. Homogenization methods, the role of dissipation, spatial dispersion (SD), and slow plasmon-polaritons are reviewed. The feasibility of obtaining the hyperbolic dispersion law in a macroscopic description of DP of inserts using the Drude–Lorentz model is studied. In the general case with dissipation and SD, the surface of the Fresnel-equation isofrequencies is shown to differ from a rotation hyperboloid and to be bounded. The ambiguity of a description based on effective material parameters, the effect of dissipation and SD on hyperbolicity, currently observable and possible physical phenomena, and HMM applications are discussed.

Terahertz Artificial Dielectric Lens.

We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices.

Spectral and polarization properties of stochastic electromagnetic beams propagating in gain or absorbing media

Based on the generalized Huygens–Fresnel diffraction principle and on the unified theory of coherence and polarization of light, the analytical expressions for the cross-spectral density matrix of a class of stochastic electromagnetic beams in linear, deterministic media with gain or absorption, in which the wave number is generally complex, has been derived. In particular, through numerical examples based on our analytical formulas the behavior of the spectral density, and of the degree of polarization of the Electromagnetic Gaussian Schell-model is analyzed. It is demonstrated how these statistical properties of the beam propagating in such media depend on the properties of the source and on the wave number of the medium. Numerical examples relate to two model sources: with uncorrelated and partially correlated mutually orthogonal transverse components of the electric field. The results will impact potential applications involving natural absorbing media, such as oceanic waters, and man-made media such as active lasers, for instance.

Artifical chiral materials

In 1898 Acharya J C Bose, a researcher from Calcutta, India, wrote in the Proceedings of the Royal Society of London: 'In order to imitate the rotation by liquids like sugar solutions, I made elements of molecules of twisted jute, of two varieties, one kind being twisted to the right (positive) and the other twisted to the left (negative).... The twisted structure produces an optical twist of the plane of polarization'. This paper[1], published 111 years ago and reporting experimental microwave tests on the optical activity of the artificial chiral medium, was the first publication on what has now become a flourishing and dynamic field of metamaterials - man-made media with all sorts of unusual functionalities that can be achieved by artificial structuring smaller than the wavelength scale of the external stimulus. An increasing number of researchers are currently designing, fabricating and studying artificial metamaterials composed of tailored chiral building blocks that may be viewed as 'artificial chiral molecules'. This special section is devoted to this vibrant and emerging research direction and has a special emphasis on the theory of light interactions with artificial chiral media.