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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The design, synthesis, and characterization of polymethine dyes for all-optical signal processing applications

Matichak, Jonathan D. 13 April 2010 (has links)
Material development is necessary before all-optical signal processing (AOSP) can be realized. Traditional AOSP will require materials with a large magnitude of the real part of the third-order polarizability, while having a small imaginary magnitude of third-order polarizability. The aim of this thesis is to investigate the potential for polymethine dyes to be used for AOSP applications. The basic structure of a polymethine dye was synthetically modified in a variety of positions to observe the effects upon the linear and nonlinear optical properties. The modifications included variation in the terminal group, substituents in the polymethine bridge, and exchange of the counterion. The dyes were generally synthesized using the Vilsmeyer-Haack reaction to form simple polymethine precursors, and then complexity was added by performing the Knoevenagel condensation with various acceptors and the polymethine precursor. Ion metathesis was often employed to exchange the initial counterion for a counterion that provided increased solubility in common organic solvents. The third-order nonlinear optical polarizabilities were characterized by Dr. Joel Hales who used the open- and closed-aperture Z-scan technique at 1300 nm and non-degenerate two-photon absorption experiments to identify the position of the two-photon absorption bands.
2

Vers des métamatériaux intégrés à pertes compensées : modélisation / Towards integrated and loss-compensated metamaterials : modelling

Le Cunff, Loïc 24 November 2014 (has links)
Au cours des dernières décennies, les métamatériaux ont montré qu'ils pouvaient avoir des propriétés étonnantes, permettant d'imaginer et de réaliser des dispositifs tels que des lentilles à indice négatif, des dispositifs de camouflage ou des lentilles parfaitement plates. Aussi, font-ils aujourd'hui l'objet d'une intense recherche. Cette thèse, inscrite dans le projet ANR METAPHOTONIQUE, avait pour objectif principal d'étudier la possibilité d'utiliser des métamatériaux pour l'optique guidée à la longueur d'onde télécom. Ceci a requis une meilleure compréhension du comportement des métamatériaux, ce qui nous a orientés vers l'étude de modèles effectifs. La récupération des paramètres optiques effectifs a nécessité de pouvoir simuler la réponse des métamatériaux sous une illumination en incidence oblique, ce qui a requis l'implémentation de telles méthodes en FDTD. Aux cours de nos travaux, nous avons aussi mis en évidence un phénomène de rotation de la polarisation de modes guidés suite à leur interaction avec des métamatériaux asymétriques. Nous avons alors pu concevoir et caractériser un dispositif pour l'optique guidée destiné faire tourner la polarisation de la lumière sur une longueur deux fois plus courte que la longueur d'onde. Enfin, un objectif secondaire a été de déterminer si les pertes dues à la présence de nanostructures métalliques dans nos métamatériaux pouvaient être compensées grâce à l'utilisation de matériaux à gain. Un modèle permettant de décrire de tels matériaux en FDTD a donc été étudié et implémenté / Over the last decades, metamaterials have been shown to exhibit extraordinary properties. These properties could allow the design of new devices such as negative refractive index lenses, cloaking devices and perfectly flat lenses. This PhD is part of the ANR METAPHOTONIQUE project and its main objective was to study the potential of metamaterials for integrated photonics at telecommunication wavelengths. This required to first better understand the behavior of metamaterials, which led us to study effective index models. The retrieval of effective optical parameters required to be able to simulate the optical response of metamaterials under oblique incidence excitation. Due to this, we had to study and implement such methods for FDTD computations. Our work also showed that asymmetrical metamaterials possessed the ability to make the polarization of guided modes rotate. This allowed us to design and characterize a potential device for integrated photonics, which effectively converts the polarization of guided modes over lengths shorter than half the wavelength. A secondary goal of this PhD was to study the potential compensation of losses occuring within the metallic nanostructures of our metamaterials through the use of materials with gain. Thus, a model allowing us to simulate such materials in FDTD has been implemented

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