Engineering Metamaterials and Photonic Crystals in the Microwave Regime: from Superlensing to Slow-Light
Creators: name: Savo, Salvatore
Publisher: name: Università degli Studi di Napoli Federico II
Year: 2009

description: The following work involves the study of electromagnetic properties at the microwave
frequency range of a class of materials called Metamaterials. A metamaterial is an
artificial composite material that exhibits an electromagnetic response unlike any
that have been observed in nature or constituent materials themselves. Usually, the
response results from artificially fabricated, extrinsic or low dimensional inhomogeneities.
In the last decade, metamaterials have provided scientists with an alternative
and reliable way to experimentally study effects that could have never been
achieved using conventional materials. The most astonishing of these effects was
the concept of negative refraction, which was first theorized by the Russian scientist
Victor Veselago in 1968. Since then, the publications of milestone works by
Eli Yablonovitch and Sajeev John (in 1987), and Sir John Pendry (in 1999),
have triggered enormous interest in metamaterials research, and have resulted in a
tremendous number of theoretical and experimental works in field of metamaterials
worldwide.
This study focuses on how metamaterials can be integrated into the process of molding
the flow of light. This dissertation is divided into two main parts. It will begin
with an introduction to the world of metamaterials and their applications, and will
then branch out into two sections, with each section devoted to a specific type of
periodic metamaterial, Photonic Crystals (PCs), and Split Ring Resonators (SRRs).
The first part of the thesis will investigate Photonic Crystals. Photonic Crystals are
made of a periodic, or quasi-periodic, arrangement of dielectric elements that show
unique properties in a diffraction regime when a wavelength is comparable to the unit cell size. For this study, I will investigate, both numerically and experimentally,
the electrodynamic properties of photonic crystals, focusing the attention first, to the
anomalous diffraction phenomena of two-dimensional (2D) PCs proving at microwave
the Pendell¨osung effect, which is a physical effect of the Dynamical Diffraction Theory.
Positive agreement between the numerical simulations and measurements carried
out in a parallel plate waveguide have been found. Second, I will focus extensively
on the subwavelength properties of one-dimensional PCs made with slanted dielectric
bars by experimentally demonstrating, for the first time, the superlensing capabilities
of 1D structures in the microwave regime. Finally, I will numerically analyze the
improvement of the focusing capacity induced by the introduction of a proper surface
corrugation.
Part two of the dissertation will focus on Split Ring Resonators (SRRs) which are
made of arrays of metallic resonant elements that show their anomalous properties in
the effective regime when the wavelength is much larger than the unit cell dimension.
I will examine, from the numerical and experimental point of view, the electromagnetic
properties of metamaterial media made with split ring resonators, focusing the
attention on a full comprehension of their transmission properties. I will also discuss
the Slow Light properties of a planar waveguide made with a dielectric core, and a
single negative index cladding made with SRRs. Today, the concept of slowing light
is popular because of the potential benefits it could have on a variety of real life applications.
In fact, low group velocities control light propagation from microwave to
optical frequencies, and could lead to several more applications including delay line
filters and phase shifters. Moreover, the field of slow light, such as those belonging
to the properties of PCs used for manipulating light, is fundamental for the future of
integrated photonic chips.
All the experimental characterizations presented in this dissertation have been
done at microwave wavelengths by sandwiching the samples in a parallel plate waveguide.
The characterization of the metamaterials transmission properties was accomplished by using antennas connected to a Vector Network Analyzer that serviced in
measuring the phase and amplitude of the signal. Finally, the slow light properties
were analyzed by measuring the electromagnetic pulse delay using a Microwave Transition
Analyzer. The results outlined in the first part of this dissertation were carried
out at the University of Naples “Federico II” during the first year and a half of my
PhD studies, while the results from part two were made possible at the Electronic
Material Research Institute at Northeastern University in Boston, where I spent the
second half of my PhD. This dissertation is the result of a long term scientific collaboration
between the two above mentioned universities, which are both interested in
investigating the properties of metamaterials. As a result of this collaboration, the
scholarship that supported me during the three years of my PhD was cofunded by
both institutions.