Controlling light with metadevices

Abstract

The development of metamaterials provides a new way to manipulate electromagnetic waves by sub-wavelength artificial structures, and hence brings new properties and functionalities that cannot be found with conventional materials. This leads to the possibility of previously unthought-of applications, including perfect lenses, invisibility cloaks, and perfect absorbers. However, several critical challenges need to be addressed before transiting from intriguing scientific findings to real-world usable devices. This dissertation deals with two challenges regarding the practical use of metamaterials. Firstly, fabrication of truly three-dimensional (3D) and large-scale metamaterials is needed to increase the degrees of freedom of the functionality for device level applications. Direct laser writing (DLW) technique is a potential choice to fabricate such materials with special design requirements. A hyperbolic metamaterial and a hollow waveguide with negative index metamaterial cladding that satisfy the vertical connectivity requirement are proposed, and hence they have the potential to be fabricated with DLW. Three different magnetic dipoles supported by the hyperbolic metamaterial are investigated and contribute to hyperbolic dispersion. In addition, the adverse effect of material absorption on the hollow waveguide with negative index cladding is studied, which leads to the second challenge: how to avoid losses. A loss compensation technique called the plasmon injection (Π) scheme is successfully applied to an experimental hyperlens and a magnifying superlens. The extension of this Π scheme to the hyperlens is analytically described and numerically implemented. The equivalent of the spatial filter with the Π scheme is demonstrated and the resolution enhancement is obtained for both the hyperlens and the magnifying superlens. In addition, this dissertation also provides a possible solution to meet the need for miniaturized devices. Metamaterials have potential advantages compared with conventional materials for compact design due to their sub-wavelength unit cells and arbitrary control of electromagnetic responses. An extremely sub-wavelength negative index metamaterial (NIM) working at radio frequency (RF) is proposed. The idea of improving the transparency of the metamaterial by reducing the diluted plasma frequency is investigated. Meanwhile, at optical frequencies, a metamaterial-based beam splitter is proposed and able to achieve polarizing, partially polarizing and non-polarizing properties by changing its geometry.