Transformation optics

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

Moulding the flow of surface plasmons using conformal and quasiconformal mappings

Abstract: In this paper, we analyze how transformation optics recipes can be applied to control the flow of surface plasmons on metal–dielectric interfaces. We study in detail five different examples: a cylindrical cloak, a beam shifter, a right-angle bend, a lens and a ground-plane cloak. First, we demonstrate that only the modification of the electric permittivity and magnetic permeability in the dielectric side can lead to almost perfect functionalities for surface plasmons. We also show that, thanks to the quasi two-dimensional (2D) character of surface plasmons and their inherent polarization, applying conformal and quasiconformal mapping techniques allows one to design plasmonic devices in which only the isotropic refractive index of the dielectric film needs to be engineered.

Ultrabroadband Terahertz Absorption by Uniaxial Anisotropic Nanowire Metamaterials

Abstract: Three-dimensional structure terahertz metamaterial absorbers with the properties of ultrabroadband and polarization-insensitive absorption were proposed. Different from the recent designs of the multilayer horizontal configurations, our design consists of the uniaxial anisotropic gold nanowire arrays that are filled in the frustum pyramid dielectric medium. The principle for the ultrabroadband absorption originates from the overlapping of the different but very closely positioned electromagnetic resonances. Each resonance frequency follows the equation of the odd multiple of the quarter wavelengths, which can be flexibly controlled by varying the height of the corresponding gold nanowires. In addition to the great prospect for the potential applications in terahertz, our design could also be easily extended to the other frequency regimes for a host of applications such as electromagnetic stealth, infrared detection, imaging, and solar cell.

Restoring in-phase emissions from non-planar radiating elements using a transformation optics based lens

Abstract: The broadband directive in-phase emission from an array of sources conformed cylindrically is numerically and experimentally reported. Such manipulation is achieved through the use of a lens designed by transformation optics concept. The all-dielectric lens prototype is realized through three-dimensional (3D) polyjet printing and presents a graded refractive index. A microstrip antenna array fabricated using standard lithography techniques and conformed on a cylindrical surface is used as TE-polarized wave launcher for the lens. To experimentally demonstrate the broadband focusing properties and in-phase directive emissions, both the far-field radiation patterns and the near-field distributions have been measured. Experimental measurements agreeing qualitatively with numerical simulations validate the proposed lens and open the way to inexpensive all-dielectric microwave lenses for beam forming and collimation.

Dispersion characteristics of silicon nanorod based carpet cloaks.

Abstract: A wide range of transformation media designed with conformal mapping are currently being studied extensively due to their favorable properties: isotropy, moderate index requirements, low loss and broad bandwidth. For optical frequency operation, the transformation media are commonly fabricated on high index semiconductor thin films. These 2D implementations, however, inevitably introduces waveguide dispersion, which affects the bandwidth and loss behavior. In this paper, for carpet cloaks implemented by a silicon nanorod array, we have confirmed that waveguide dispersion limits the bandwidth of the transformation medium by direct visualizing the cut-off conditions with near-field scanning optical microscopy (NSOM). Furthermore, we have experimentally demonstrated the extension of cut-off wavelength by depositing a conformal dielectric layer. This study illustrates the constraints on the 2D transformation media imposed by the waveguide dispersion and suggests a general technique to tune and modify their optical properties.

Perfect imaging in the optical domain using dielectric materials

Abstract: The promise of perfect imaging in the optical domain, where light can be imaged without aberrations and with ultra-high resolution, could revolutionize technology and nanofabrication [1, 2, 3, 4, 5, 6]. Recently it has been shown theoretically that perfect imaging can be achieved in a dielectric medium with spatially varying refractive index [7, 8]. The lens geometry is defined using transformation optics [9, 10, 11, 12, 13, 14, 15] for projecting a spherical space onto a real plane space, forming Maxwells fish eye [16, 17, 18, 19]. Most transformation optics demonstrations have been achieved for Euclidean spaces and in the microwave regime, due to ease of fabrication. Here we demonstrate a transformation to a non-Euclidean space [20] in the optical regime using silicon nanophotonic structures.