Thesis (M.Eng.)--University of Wollongong, 2006. / Typescript. Includes bibliographical references: leaf 101-106.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1997. / Vita. Abstract. Includes bibliographical references (leaves 148-155). Also available electronically via Internet.

Les éléments de diffraction sont largement utilisés aujourd'hui dans un nombre grandissant d'applications grâce à la progression des technologies de microstructuration dans le sillage de la micro-électronique. Pour un design optimal de ces éléments, des méthodes de modélisation précises sont nécessaires. Plusieurs méthodes ont été développées et sont utilisées avec succès pour des réseaux de diffraction unidimensionnel de différents types. Cependant, les méthodes existantes pour les réseaux deux dimensionnel ne couvrent pas tous types de structures possibles. En particulier, le calcul de l'efficacité de diffraction sur les réseaux métalliques à deux dimensionnel avec parois verticales représente encore une grosse difficulté pour les méthodes existantes. Le présent travail a pour objectif le développement d'une méthode exacte de calcul de l'efficacité de diffraction de tels réseaux qui puisse servir de référence. La méthode modale développée ici - dénommée ,,true-mode" en anglais - exprime le champ électromagnétique sur la base des vrais modes électromagnétiques satisfaisant les conditions limites de la structure 2D à la différence d'une méthode modale où les modes sont ceux d'une structure approchée obtenue, par exemple, par développement de Fourier. L'identification et la représentation de ces vrais modes à deux dimensions restait à faire et ce n'est pas le moindre des résultats du présent travail que d'y avoir conduit. Les expressions pour la construction du champ sont données avec des exemples de résultats concrets. Sont aussi fournies les équations pour le calcul des intégrales de recouvrement et des éléments de la matrice de diffusion / Diffractive elements are widely used in many applications now as the microstructuring technologies are making fast progresses in the wake of microelectronics. For the optimization of these elements accurate modeling methods are needed. There exists well-developed and widely used methods for one-dimensional diffraction gratings of different types. However, the methods available for solving two-dimensional periodic structures do not cover all possible grating types. The development of a method to calculate the diffraction efficiency of two dimensional metallic gratings represents the objective of this work. The one-dimensional true-mode method is based on the representation of the field inside the periodic element as a superposition of particular solutions, each one of them satisfying exactly the boundary conditions. In the developed method for the two-dimensional gratings the representation of the field within the grating in such way is used. In the present work, the existing modal methods for one-dimensional gratings can be used as the basis for the construction of the modal field distribution functions within two-dimensional gratings. The modal function distributions allow to calculate the overlap integrals of the fields outside the grating with those within the structure. The transition matrix coefficients are formed on the basis of these integrals. The final stage is the calculation of the scattering matrix based on two transition matrices. The equations for the field reconstruction are provided and accompanied by examples of results. Further equations used to calculate the overlap integrals and scattering matrix coefficients are provided

Les propriétés optiques des nanomatériaux, tels que les cristaux photoniques ou les métamatériaux, ont reçu beaucoup d’attention dans les dernières années [1–9]. La dérivation numérique de ces propriétés se révèle pourtant très compliquée, en particulier dans le cas des structures métallo-diélectriques, qui comportent des résonances plasmoniques. C’est pourquoi des méthodes numériques avancées et des modèles semi-analytiques sont nécessaires. Dans cette thèse, nous montrerons que le formalisme de la matrice de diffraction peut satisfaire ces deux aspects. La méthode de la matrice de diffraction est un concept très général en physique. Dans le cas des structures périodiques, on peut dériver la matrice de diffraction à l’aide de la méthode modale de Fourier [10]. Pour la description exacte des géométries planes, nous avons développé la méthode des coordonnées adaptées [11], qui nous donne un nouveau système de coordonnées, dans lequel les interfaces des matériaux sont des surfaces de coordonnées constantes. En combinaison avec la méthode de la résolution spatiale adaptative, la méthode des coordonnées adaptées permet d’améliorer considérablement la convergence de la méthode modale de Fourier, de telle sorte qu’on peut calculer des structures métalliques compliquées très efficacement. Si on utilise la matrice de diffraction, il est non seulement possible de dériver les propriétés optiques en illumination de champ lointain, comme la transmission, la réflexion, l’absorption, et le champ proche, mais aussi de décrire l’émission d’un objet à l’intérieur d’une structure et d’obtenir les résonances optiques d’un sytème. Dans cette thèse, nous présenterons une méthode efficace pour la dérivation des résonances optiques tridimensionnelles, utilisant directement la matrice de diffraction [14]. Si on connaît les résonances d’un système isolé, il est aussi possible d’obtenir une approximation des résonances dans le cas d’un système combiné à l’aide de notre méthode du couplage des résonances [15, 16]. Cette méthode permet de décrire le régime de couplage des champs lointain et proche, y compris le couplage fort avec les résonances Fabry-Perot, pour des systèmes qui se composent d’un empilement de deux structures planes et périodiques. Pour cette raison, on peut étudier efficacement le couplage de ces systèmes. Cette thèse est écrite de manière à donner une idée d’ensemble du formalisme de la matrice de diffraction et de la méthode modale de Fourier. En outre, nous décrivons notre généralisation de ces méthodes et nous montrons la validité de nos approches pour différents exemples. / The optical properties of nanostructures such as photonic crystals and metamaterials have drawn a lot of attention in recent years [1–9]. The numerical derivation of these properties, however, turned out to be quite complicated, especially in the case of metallo-dielectric structures with plasmonic resonances. Hence, advanced numerical methods as well as semi-analytical models are required. In this work, we will show that the scattering matrix formalism can provide both. The scattering matrix approach is a very general concept in physics. In the case of periodic grating structures, the scattering matrix can be derived by the Fourier modal method [10]. For an accurate description of non-trivial planar geometries, we have extended the Fourier modal method by the concept of matched coordinates [11], in which we introduce a new coordinate system that contains the material interfaces as surfaces of constant coordinates. In combination with adaptive spatial resolution [12,13], we can achieve a tremendously improved convergence behavior which allows us to calculate complex metallic shapes efficiently. Using the scattering matrix, it is not only possible to obtain the optical properties for far field incidence, such as transmission, reflection, absorption, and near field distributions, but also to solve the emission from objects inside a structure and to calculate the optical resonances of a system. In this work, we provide an efficient method for the ab initio derivation of three-dimensional optical resonances from the scattering matrix [14]. Knowing the resonances in a single system, it is in addition possible to obtain approximated resonance positions for stacked systems using our method of the resonant mode coupling [15, 16]. The method allows describing both near field and far field regime for stacked two-layer systems, including the strong coupling to Fabry-Perot resonances. Thus, we can study the mutual coupling in such systems efficiently. The work will provide the reader with a basic understanding of the scattering matrix formalism and the Fourier modal method. Furthermore, we will describe in detail our extensions to these methods and show their validity for several examples.

Ce travail de thèse porte sur l'étude des processus non-linéaires cohérents des semiconducteurs nanostructurés en microcavité. Cette étude montre la faisabilité d'une porte optique ultra-rapide et peu dissipative fonctionnant avec une faible énergie de commande (~µJ/cm²). Des études expérimentales en diffraction et en pompe-sonde dégénérées ont été réalisées sur des microcavités semiconductrices, à température ambiante. Elles ont permis de mettre en évidence une modulation ultra-rapide de la fonction diélectrique du semiconducteur lorsque l'on excite le matériau dans sa région de transparence. Un rendement de diffraction de 2% et une modulation de réflectivité d'un contraste 5:1 ont été mesuré pour une excitation de faible énergie (~µJ/cm²). Cette modulation ultra-rapide a été attribuée à l'effet Stark optique. L'insertion du matériau non-linéaire dans une microcavité Fabry-Pérot permet d'exalter l'interaction lumière/matière et ainsi d'abaisser l'intensité de commande. Une étude numérique d'une microcavité contenant un milieu absorbant a été réalisée. Nous avons montré que le minimum de réflectivité ne se produit pas forcément à la longueur d'onde de résonance lres attendue mais en une longueur d'onde dite de pseudo-résonance lps. Le décalage entre ces deux longueurs d'onde peut atteindre plusieurs nanomètres. En considérant cette étude, une modélisation du couplage de l'effet Stark optique avec le mode de la cavité a également été réalisée. Le modèle développé permet de rendre compte des résultats expérimentaux de modulation de réflectivité. L'utilisation de ce modèle permettrait d'étudier l'influence des paramètres d'élaboration de la cavité sur la modulation et ainsi de définir une structure adaptée à la modulation.

Orientador: Luís Eduardo Evangelista de Araujo / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-18T17:59:31Z (GMT). No. of bitstreams: 1 Carvalho_SilvaniaAlvesde_D.pdf: 4970692 bytes, checksum: f260af26ecacc7e92b1246968850ff9b (MD5) Previous issue date: 2011 / Resumo: Nesta tese apresentamos o estudo teórico de grades de difração induzidas em meios atômicos na condição de transparência induzida eletromagneticamente (EIT). As grades atômicas que serão descritas baseiam-se na não-linearidade Kerr gigante exibida pelos átomos sob EIT. No primeiro estudo realizado, a grade atômica é gerada a partir da modulação da não-linearidade Kerr através de uma onda estacionária. Neste estudo, aplicamos a teoria de ondas acopladas, desenvolvida originalmente para grades acústicas e holográficas, para a grade atômica de modo a obter uma expressão analítica para a eficiência de difração em primeira ordem. Altas eficiências de difração de um feixe de prova ressonante são previstas para incidência próxima ao ângulo de Bragg. Em um segundo estudo, descrevemos uma grade atômica do tipo ¿blazed¿ criada através da inserção de uma máscara de intensidade em um dos feixes responsáveis pela não-linearidade Kerr do meio. Eficiências de difração em primeira ordem para o feixe de prova próximas a 100% foram obtidas. Por último, discutimos uma grade de difração induzida na condição de coerência máxima entre os estados fundamentais de um átomo. Esta grade difrata não somente o feixe de prova incidente, mas também um segundo feixe gerado por mistura de quatro ondas. Apesar desta última grade apresentar eficiência de difração muito menor do que as duas grades anteriores, esta grade pode operar em vários comprimentos de onda diferentes, embora envolva sempre um feixe ressonante com alguma transição atômica. Além da contribuição teórica, trabalhos experimentais relacionados à área de aprisionamento e resfriamento de átomos foram realizados. Inicialmente, um experimento de espectrocopia de fotoassociação próximo ao limite de dissociação em uma amostra de 85Rb é apresentado. Em seguida, uma fonte de laser em 423 nm, formada por um laser de Ti-Sa com dobramento intracavidade através de um cristal LBO, que foi construída e estabilizada é descrita / Abstract: In this thesis we present a theoretical study on induced diffraction gratings in atomic media under electromagnetically induced transparency condition. The atomic gratings which will be described are based on the giant Kerr nonlinearity displayed by the atoms under EIT. In the first study, the atomic grating is generated from the modulation of the Kerr nonlinearity through a stationary wave. In this study, we apply coupled wave theory, originally developed for acoustic and holographic gratings, for an atomic grating in such a way that an analytical expression for the first order diffraction is obtained. High diffraction efficiencies of the resonant probe beam are predicted for incidence near Bragg angle. In a second study, we describe a blazed-type atomic grating created through the insertion of an intensity mask in one of the beam responsible for the Kerr nonlinearity of the medium. First order diffraction for the probe beam near 100% efficiency was observed. Finally, we discuss a diffraction grating induced under maximum coherence condition between the ground states of an atom. This grating diffracts not only the probe beam, but also a second beam generated by four wave mixing. Although this last grating shows a diffraction efficiency much smaller than the previous one, this grating can operate in several wavelengths, although involving a beam resonant with an atomic transition. Besides the theoretical contribution, experimental works related to the cooling and trapping of atoms were implemented. Initially, an experiment of photoassociation spectroscopy near the dissociation limit in a sample of cold rubidium atoms is presented. Following, a homebuilt laser source at 423 nm formed by a Ti-Sapphire laser with intracavity frequency doubling through a LBO crystal that was stabilized is described / Doutorado / Física Atômica e Molecular / Doutora em Ciências

Orientador: Jose Antonio Siqueira Dias / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-15T01:30:18Z (GMT). No. of bitstreams: 1 Costa_EduardoFerreirada_M.pdf: 6728170 bytes, checksum: 22e2ac4dad3b06f3f61e0ece70fa2f5d (MD5) Previous issue date: 2009 / Resumo: Por serem eletricamente passivos e imunes à interferência eletromagnética, os sensores a fibra óptica estão se tornando uma excelente escolha para o sensoreamento em várias aplicações, como aeroespacial, distribuição e geração de energia elétrica, transportes ferroviários, e equipamentos de segurança militares. Entre outras vantagens está o fato de que os sinais medidos podem ser transmitidos em distâncias muito grandes (da ordem de quilômetros), são compactos e leves. A técnica de medida convencional com sensor à FBG necessita de equipamentos de custo muito elevado, tornando-se inviável para aplicações de baixo custo. Neste trabalho apresenta-se uma nova técnica para medir temperatura com sensores a fibra óptica com grades de Bragg. Resultados experimentais de medidas feitas com a técnica desenvolvida mostram que é possível obter uma resolução de 0,5 mºC em medidas realizadas numa faixa de 30ºC. / Abstract: Due to the characteristic of being electrically passive and immune to electromagnetic interference, optical fiber sensors are becoming an excellent choice for several applications, as aerospace, distribution and generation of electrical energy, railway transports, and military equipment. Among other advantages, these sensors are compact, light and the measured signals can be transmitted for very long distances (in the order of kilometers). The existing techniques for temperature measurement using FBG sensors need expensive equipments, and therefore are not suitable for low cost applications. In this work a new technique to measure temperature with a extremely high resolution using FBG sensors is presented. Experimental results of measurements carried out with the proposed technique show that a resolution of 0.5 m°C was obtained for measurements performed over a 30 ºC temperature range. / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica

Orientadores: Hugo Enrique Hernandez Figueroa , Júlio César Rodrigues Fernandes de Oliveira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-26T03:17:30Z (GMT). No. of bitstreams: 1 Freitas_AlexandrePassos_M.pdf: 2935936 bytes, checksum: 2bf660b1a9d7a183bc552d3db9da1b97 (MD5) Previous issue date: 2014 / Resumo: O crescente aumento da demanda de tráfego de dados dos sistemas de comunicação ópticos em conjunto com a busca da integração e miniaturização cada vez maior dos componentes impulsionaram a fotônica integrada em silício como uma das tecnologias promissoras para a evolução das novas gerações de dispositivos ópticos. Esta tecnologia, além de possuir suas características de um alto contraste de índice de refração, capacidade de modulação óptica através de controle de temperatura ou por densidade de portadores, se utiliza da infra-estrutura de fabricação para a indústria de microeletrônica já desenvolvida nas últimas décadas. Neste cenário, este trabalho propõe o desenvolvimento de um modulador de fase fabricado com a tecnologia de fotônica integrada em silício para o formato de modulação DP-QPSK e que opere na banda C de comunicação óptica. Análises de simulações e experimentais foram realizadas para a validação do fluxo de desenvolvimento do circuito e de cada componentes utilizado individualmente / Abstract: The increasing demand for data in optical communication systems with a constant search for reduction of device dimensions boosted silicon photonics as a candidate technology to the following optical device generations. Besides having high refractive index contrast, modulation capabilities through thermal or by carrier density control, this technology takes advantage of the microelectronic infra-structure developed in the last decades to fabricate small optical components with high reliability. In this scenario, this dissertation proposes the design of a phase modulator in silicon photonic technology. This modulator is able to operate at C-band and make the DP-QPSK modulation. Simulation and experiment analysis were made to validate the design flow for the optical circuit and for each single component / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

Reliability and sensitive information protection are critical aspects of integrated circuits. A novel technique using near-field evanescent wave coupling from two subwavelength gratings (SWGs), with the input laser source delivered through an optical fiber is presented for tamper evidence of electronic components. The first grating of the pair of coupled subwavelength gratings (CSWGs) was milled directly on the output facet of the silica fiber using focused ion beam (FIB) etching. The second grating was patterned using e-beam lithography and etched into a glass substrate using reactive ion etching (RIE). The slightest intrusion attempt would separate the CSWGs and eliminate near-field coupling between the gratings. Tampering, therefore, would become evident. Computer simulations guided the design for optimal operation of the security solution. The physical dimensions of the SWGs, i.e. period and thickness, were optimized, for a 650 nm illuminating wavelength. The optimal dimensions resulted in a 560 nm grating period for the first grating etched in the silica optical fiber and 420 nm for the second grating etched in borosilicate glass. The incident light beam had a half-width at half-maximum (HWHM) of at least 7 µm to allow discernible higher transmission orders, and a HWHM of 28 µm for minimum noise. The minimum number of individual grating lines present on the optical fiber facet was identified as 15 lines. Grating rotation due to the cylindrical geometry of the fiber resulted in a rotation of the far-field pattern, corresponding to the rotation angle of moiré fringes. With the goal of later adding authentication to tamper evidence, the concept of CSWGs signature was also modeled by introducing random and planned variations in the glass grating. The fiber was placed on a stage supported by a nanomanipulator, which permitted three-dimensional displacement while maintaining the fiber tip normal to the surface of the glass substrate. A 650 nm diode laser was fixed to a translation mount that transmitted the light source through the optical fiber, and the output intensity was measured using a silicon photodiode. The evanescent wave coupling output results for the CSWGs were measured and compared to the simulation results.

In my research work, I study diffraction by planar periodic structures (diffraction grating). In the first chapter, I try to familiarize the importance of diffraction gratings in spectroscopy. The second chapter explains the basic principle of diffraction without involving difficult mathematical tools. In the third chapter, I deduce Fourier modal method from Maxwell equations, a modern mathematical approach used for calculating the electromagnetic response of diffraction. The most important part of my work consists of the fourth and fifth chapter. At first, I try to utilize Fourier modal method for deriving formulas involving just 0th and (-1)st diffraction orders. Because of the unreasonable difficulty of uncovered formulas, I decided to consider only a special case - so-called Littrow configuration, in which the solution can be superposed from symmetric and antisymmetric couples of rays. I further develop so-called Local modal method - very inaccurate, but mathematically fairly simple, and discuss its physical limitations. Whole work is finished by the sixth chapter, which compares accurate computations gained from simulation and derived analytical formulas for both methods.