UC Berkeley

Metamaterials, which are artificially engineered composites, have been shown to exhibit electromagnetic properties not attainable with naturally occurring materials. The use of such materials has been proposed for numerous applications including sub-diffraction limit imaging and electromagnetic cloaking. While these materials were first developed to work at microwave frequencies, scaling them to optical wavelengths has involved both fundamental and engineering challenges. Among these challenges, optical metamaterials tend to absorb a large amount of the incident light and furthermore, achieving devices with such materials has been difficult due to fabrication constraints associated with their nanoscale architectures. The objective of this dissertation is to describe the progress that I have made in overcoming these challenges in achieving low loss optical metamaterials and associated devices.

The first part of the dissertation details the development of the first bulk optical metamaterial with a negative index of refraction. This metamaterial is shown to overcome the problems of previous metamaterials by reducing the amount of light absorbed in the material. The increased thickness of the bulk metamaterial also allows the first direct experimental observation of negative refraction at optical frequencies. Next, I will describe the design and experimental realization of the first electromagnetic cloak operating at optical frequencies. The cloaking device is designed using quasi-conformal mapping which enables the use of an all dielectric, isotropic metamaterial, allowing the cloak to operate over large bandwidth with low absorption losses, overcoming the problems with previous cloaking proposals. This design methodology and metamaterial system is then extended to realize an optical `Janus' device. The device is designed and experimentally proven to have two different and independent optical functionalities in two separate spatial directions for use in integrated photonics architectures. The last section of the thesis describes several new directions I am pursuing in the field of metamaterials. The first is the experimental realization a photonic black hole. This device functions similar to a gravitational black hole in that it concentrates light into a small spatial area but is realized through a spatial varying index profile. The extension of transformation optics into plasmonic systems is then presented. Experimental work aimed at realizing a gradient index Luneburg lens is presented utilizing modulations of the surface plasmon mode index though height variations in a dielectric. Finally, a new method for achieving large scale, three dimensional, gradient index metamaterials is presented. Such a method could be employed for achieving large scale cloaks or gradient index lenses for use in photovoltaics.

The findings presented here represent some of the first metamaterial inspired devices at optical wavelengths. It is my hope that this work will help to inspire the next generation of metamaterials and devices with ever increasing functionality.