Transformation optics

About: Transformation optics is a research topic. Over the lifetime, 2687 publications have been published within this topic receiving 102378 citations.

Information metamaterials and metasurfaces

Abstract: Traditionally, “metamaterials” have been described by effective medium parameters due to the subwavelength nature of unit particles. The continuous nature of medium parameters makes traditional metamaterials behave as analog metamaterials. Recently, the concept of coding metamaterials or “metasurfaces” has been proposed, in which metamaterials are characterized by digital coding particles of “0” and “1” with opposite phase responses. It has been demonstrated that electromagnetic waves can be manipulated by changing the coding sequences of “0” and “1”. The coding particles provide a link between the physical world and digital world, leading to digital metamaterials and even field programmable metamaterials, which can be used to control electromagnetic waves in real time. The digital coding representation of metamaterials or metasurfaces can also allow the concepts and signal processing methods in information science to be introduced to physical metamaterials, thereby realizing extreme control of electromagnetic waves. Such studies have set the foundation of information metamaterials and metasurfaces. In this review article, the coding, digital, and field programmable metamaterials and metasurfaces are systematically summarized and analyzed with particular emphases on the information and digital convolution aspects. The future trend of information metamaterial/metasurface is predicted, including software-defined metamaterials/metasurfaces and cognitive metamaterials/metasurfaces.

Plasmonic Luneburg and Eaton lenses

Abstract: Plasmonics takes advantage of the properties of surface plasmon polaritons, which are localized or propagating quasiparticles in which photons are coupled to the quasi-free electrons in metals. In particular, plasmonic devices can confine light in regions with dimensions that are smaller than the wavelength of the photons in free space, and this makes it possible to match the different length scales associated with photonics and electronics in a single nanoscale device. Broad applications of plasmonics that have been demonstrated to date include biological sensing, sub-diffraction-limit imaging, focusing and lithography and nano-optical circuitry. Plasmonics-based optical elements such as waveguides, lenses, beamsplitters and reflectors have been implemented by structuring metal surfaces or placing dielectric structures on metals to manipulate the two-dimensional surface plasmon waves. However, the abrupt discontinuities in the material properties or geometries of these elements lead to increased scattering of surface plasmon polaritons, which significantly reduces the efficiency of these components. Transformation optics provides an alternative approach to controlling the propagation of light by spatially varying the optical properties of a material. Here, motivated by this approach, we use grey-scale lithography to adiabatically tailor the topology of a dielectric layer adjacent to a metal surface to demonstrate a plasmonic Luneburg lens that can focus surface plasmon polaritons. We also make a plasmonic Eaton lens that can bend surface plasmon polaritons. Because the optical properties are changed gradually rather than abruptly in these lenses, losses due to scattering can be significantly reduced in comparison with previously reported plasmonic elements.

Cloaking Devices, Electromagnetic Wormholes, and Transformation Optics

Abstract: We describe recent theoretical and experimental progress on making objects invisible to detection by electromagnetic waves. Ideas for devices that would once have seemed fanciful may now be at least approximately implemented physically using a new class of artificially structured materials called metamaterials. Maxwell's equations have transformation laws that allow for the design of electromagnetic material parameters that steer light around a hidden region, returning it to its original path on the far side. Not only would observers be unaware of the contents of the hidden region, they would not even be aware that something was being hidden. An object contained in the hidden region, which would have no shadow, is said to be cloaked. Proposals for, and even experimental implementations of, such cloaking devices have received the most attention, but other designs having striking effects on wave propagation are possible. All of these designs are initially based on the transformation laws of the equations that govern wave propagation but, due to the singular parameters that give rise to the desired effects, care needs to be taken in formulating and analyzing physically meaningful solutions. We recount the recent history of the subject and discuss some of the mathematical and physical issues involved.

Negative Refractive Index Materials

Abstract: The main directions of studies of materials with negative index of refraction, also called left-handed or metamaterials, are reviewed. First, the physics of the phenomenon of negative refraction and the history of this scientific branch are outlined. Then recent results of studies of photonic crystals that exhibit negative refraction are discussed. In the third part numerical methods for the simulation of negative index material configurations and of metamaterials that exhibit negative index properties are presented. The advantages and the shortages of existing computer packages are analyzed. Finally, details of the fabrication of different kinds of metamaterials are given. This includes composite metamaterials, photonic crystals, and transmission line metamaterials for different wavelengths namely radio frequencies, microwaves, terahertz, infrared, and visible light. Furthermore, some examples of practical applications of metamaterials are presented.

Hyperbolic metamaterials: new physics behind a classical problem

Abstract: 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.