Engineering Metamaterials and Photonic Crystals in the Microwave Regime: from Superlensing to Slow-Light
Savo, Salvatore (2009) Engineering Metamaterials and Photonic Crystals in the Microwave Regime: from Superlensing to Slow-Light. [Tesi di dottorato] (Inedito)
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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.
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