Dans les cellules solaires en couches minces de silicium, il est important de maximiser l'efficacité d'absorption, notamment afin d'atteindre une densité de courant de court-circuit (Jsc) suffisante. Pour atteindre cet objectif, nous avons développé des stratégies de piégeage de la lumière à base de cristaux photoniques (CP) simplement périodiques et des structures plus complexes, pseudo-désordonnées. Ce travail vise à intégrer de telles structures dans des cellules solaires en couches minces de silicium cristallin (c-Si). Tout d'abord, un CP à maille carrée de trous cylindriques ou de nano-pyramides inversées ont été intégrés dans cellules solaires à hétérojonction a-Si:H/c-Si en couches minces. L'absorption dans la seule couche absorbante (c-Si) est optimisée grâce à des simulations numériques utilisant la méthode de différences finies dans le domaine temporel. Le Jsc est augmenté de 56,4% (trous cylindriques) et 104,8% (nanopyramides inversées) par rapport au cas sans motif. Nous avons également examiné des structures plus élaborées, où plus un CP de trous cylindriques est introduit en face arrière. Deuxièmement, nous avons considéré des nanostructures complexes mais réalistes pseudo-désordonné, sur la base de supercellules périodiquement reproduites où les trous sont placés au hasard. Dans de telles structures l'absorption peut être augmentée par rapport à un réseau carré de trous optimisé, par augmentation de la densité spectrale de modes optiques. La simulation basée sur l'analyse rigoureuse couplée et la fabrication par lithographie par faisceau électronique et les technologies de gravure ionique réactive ont été effectués, conduisant à une augmentation de l'absorption nette d'environ 2,1% en théorie, et de 2,7% expérimentalement. Enfin, nous avons mis en place des structures pseudo-désordonnées avec supercellules de tailles différentes, dans les couches c-Si de plusieurs épaisseurs dans la gamme 1-8μm. Les mécanismes d'absorption dans ces structures ont été analysés, à la fois dans les espaces réel et réciproque, en vue de déterminer des critères de conception. En outre, la réponse angulaire de la structure pseudo-désordonnée optimisée est plus stable que celle du réseau carré optimisé, en particulier dans les grandes longueurs d'onde. / In thin film silicon solar cells, it is important to take control of the absorption efficiency, in order to reach a high enough short-circuit current density (Jsc). To reach this goal, we have developed light trapping strategies based on simply periodic photonic crystals (PC) and more complex pattern structures. This work aims at integrating such structures into thin film crystalline silicon (c-Si) solar cells. Firstly, a simply periodic square lattice PC structure of cylindrical holes or inverted nano-pyramids have been considered in a-Si:H/c-Si heterojunction thin film solar cells. The absorption in the sole absorbing layer (c-Si) is considered and optimized in numerical simulations based on the Finite Difference Time Domain method. The Jsc are increased by 56.4% (cylindrical holes) and 104.8% (inverted nano-pyramids) compared to the unpatterned case. We also considered more advanced structures where an additional cylindrical holes structure is introduced in the bottom. Secondly, we have considered complex but realistic “pseudo-disordered” nanostructures, based on periodically reproduced supercells where the holes are randomly shifted. In such structures the absorption could be increased compared with fully optimized square lattice of holes, by increasing the spectral density of optical modes. Simulation based on Rigorous Coupled Wave Analysis and fabrication by electronic beam lithography and reactive ion etching technologies have been performed, leading to a net absorption increase of about 2.1% theoretically, and 2.7% experimentally. Lastly, we have introduced pseudo-disordered structures with supercells of different size, in c-Si layers of several thicknesses in the 1-8μm range. The absorption mechanisms in such structures were analyzed, both in the real and reciprocal spaces, with a view to determine design guidelines. Moreover, the angular response of the optimized pseudo-disordered structure appears to be more stable than in the optimized square lattice of holes periodic case, especially in the long wavelength range.

Les nanocristaux de Silicium (SiNCs) de taille inférieure à 5 nm sont des matériaux qui présentent une intense photoluminescence (PL) et capables d’amplification optique. Cette dernière propriété est un pré-requis à l’obtention d’émission stimulée sous pompage optique. Atteindre l’émission stimulé (et l’effet laser) à partir de nanostructures basées sur Si est d’un intérêt particulier dans le domaine de la photonique à base de silicium. Le but de ce travail était (i) d’étudier les propriétés optiques fondamentales de SiNCs, (ii) de concevoir et de réaliser un cristal photonique présentant une efficacité d’extraction augmentée et (iii) d’explorer la possibilité d’améliorer l’amplification optique des émetteurs de lumière à base de SiNCs en les combinant avec un cristal photonique à deux dimensions. / Silicon nanocrystals (SiNCs) of sizes below approximately 5 nm are a material with an efficient room-temperature photoluminescence (PL) and optical gain. Optical gain is a prerequisite for obtaining stimulated emission from a pumped material, and the achievement of stimulated emission (and lasing) from Si-based nanostructures is of particular interest in the field of silicon photonics. The aim of this work was (i) to investigate fundamental optical properties of SiNCs, (ii) to design and prepare a photonic crystal with enhanced light extraction efficiency and (iii) to explore a possibility of enhancing optical gain of light-emitting SiNCs by combining them with a two-dimensional photonic crystal.

In this thesis, we present our original theoretical investigations of SiC microstruc-tures for extreme light control in the Reststrahlen band of Silicon Carbide (SiC), that occurs in the Mid-IR spectral regime. In this frequency regime, most of the light will be reflected from bulk SiC, due to the extreme permittivity response of SiC. However, we demonstrate that it is possible to control light to be absorbed or ultra refracted within the microstructures constructed from SiC in the Reststrahlen band of SiC. In particular, we show that this high reflective behaviour of SiC can be over-come via different mechanisms: by achieving a Photonic Crystal (PC) band-edge reflectionless condition in a SiC terminated one-dimensional (1D)-PC, by tailoring the effective phonon-polariton gap in SiC-based effective metamaterials, or by cou-pling to cavity modes in SiC structures made of rectangular-cross-section pillars. Furthermore, we demonstrate that by varying the thickness of SiC layers and filling ratio throughout SiC 1D-PC structures or by using SiC pillars of different size in a pyramid arrangement, we can achieve a broad absorption bandwidth with the SiC microstructures. This absorption control provides insight for the design of efficient thermal emitters, which can be used in thermal conversion devices. Moreover, us-ing the concept of Bloch impedance, we find that translucent spectral regions can exist in SiC 1D-PCs. This possibility is highly desirable for constructing optical components in the Mid-IR spectrum where suitable bulk highly refractive materials are rare. In addition, we also present a complete theory of propagation in lossy 1D-PCs, by systematically extending the comprehensive theory for lossless 1D-PCs. Relying on this theory, we report superbending of light, beyond 90 0 in a judiciously designed superprism constructed with a SiC 1D-PC. Since, the findings reported in this thesis are in principle applicable to any polar material, we believe that our work will inspire the design of a variety of absorptive/emissive and ultra-refractive devices across the THz/Mid-IR spectrum.

Natural precious opals consist of silica nanoparticles of uniform diameter organised in a periodic three-dimensional structure. The physical structure of the material produces the perceived colour by a process of light diffraction. The modification of light by the physical structure of the material is also known as structural colour. This is a different process from how most surface colours are produced where light is more usually absorbed by dye and/or pigment molecules. Desirable aesthetic qualities could be achieved if the structural colours produced by natural opals could be replicated in the form of a film or a coating on textile substrates. The work presented investigates how to produce structurally coloured textiles using surface applications of uniform spherical silica nanoparticles (USSNPs). A novel one-step solvent varying (SV) technique has been developed to synthesise USSNPs with particle diameters in a controlled size range. Using suspensions containing USSNPs, structurally coloured artificial opal (AO) films have been fabricated by self-assembly using a process of natural gravity sedimentation. The sedimentation of a particular particle size range of USSNPs (from which a coloured film was produced), onto the surface of fabrics, produced a structurally coloured fabric. By controlling the mean particle diameter a wide range of spectral colours from red to blue was obtained. The light fastness properties of the coloured textiles were investigated. A further surface modification of USSNPs was performed by adding vinyl functional groups to improve the mechanical strength of the structural colour. This work suggested a novel approach to colouring textile materials without using traditional dyes and/or pigments.

The majority of colours in the natural world are produced via the wavelength selective absorption of light by pigmentation. Some species of both flora and fauna, however, are particularly eye-catching and visually remarkable as a result of the sub-micron, light-manipulating architecture of their outer-integument material. This thesis describes detailed investigations of a range of previously unstudied photonic structures that underpin the creation of the interesting visual appearances of several such species of flora and fauna. These structures were examined using a variety of methods, including optical microscopy, scanning and transmission electron microscopy, focused ion-beam milling and atomic force microscopy. This enabled detailed characterisation of the species’ photonic systems. The degree of order discerned in the species’ photonic structures ranged from: ‘ordered’ systems, where multiple layers of two materials produces metallic and often mirror-like reflections; to ‘quasi-ordered’ systems, where an average periodicity of the structure in all directions gives rise to diffuse, coloured scatter; to disordered systems, where no discernible order is observed, which results in a diffuse, broad-band, white appearance. In addition to this, the range of systems also encompassed: periodicities in one-dimension in the form of multilayering; ‘quasi-two-dimensional’ structures in the form of aligned fibres; and three-dimensional structures formed from arrangements of spherical particles. Alongside this experimental characterisation, an in-depth series of supporting theoretical analyses were undertaken. For the one-dimensional systems studied here, the models’ theoretical reflectance was calculated using analytical methods. For other systems, with more complex structural-geometries, theoretical simulations of their electromagnetic response to incident radiation were carried out using finite-difference-time-domain and finite-element-method numerical modelling approaches. Theoretical modelling results were compared to experimental measurements of each sample's optical properties. These were primarily reflectance measurements, which were taken using a range of techniques appropriate for each specific investigation. In addition to this, a synthetic sample, mimicking the white-appearance and remarkable polarisation-dependant reflectance of one insect’s photonic structure, was created using polymer electrospinning. Using these experimental measurements and theoretical simulation predictions, the structural colour production mechanisms adopted by several species of flora and fauna were elucidated.

Au cours de ces 20 dernières années, une attention particulièrement soutenue a été donnée à l'étude et à la fabrication de matériaux nano-structurés permettant le contrôle de la lumière. Cependant, les propriétés de non-linéarité optique de ces nouveaux matériaux n'ont que très peu été explorées. Partant de ce constat, cette thèse se propose de pourvoir cette insuffisance. L'accent est mis en particulier sur le processus de génération de seconde harmonique à travers deux aspects fondamentaux: (i) le contrôle de l'émission de seconde harmonique pour des matériaux nano-structurés non-linéaires et (ii) l'augmentation de conversion dans des dispositifs photoniques intégrés. Nous présentons un nouveau phénomène de localisation non-linéaire qui a lieu dans des matériaux main-gauche et qui implique un accord de phase isotrope. Nous démontrons analytiquement le processus de localisation dans un milieu homogène main-gauche, avant de mettre en évidence un tel effet dans des cristaux photoniques non-linéaires à l'aide de simulations numériques. L'effet de localisation contra-propagative du second harmonique est utilisé pour le design d'une lentille de second-harmonique. Ce résultat théorique a été démontré numériquement pour une structure réalisable fonctionnant aux fréquences optiques. L'augmentation de génération de seconde harmonique constitue l'aspect complémentaire. En tirant parti de la forte localisation de lumière dans une chaîne de nano-tiges de dimension finie, nous montrons que, pris ensemble, le confinement transverse sub-longueur d'onde et la condition de résonance d'accord de phase contribuent de manière importante à l'augmentation de la génération de seconde harmonique. Les capacités de guidage sub-longueur d'onde de chaînes de nano-tiges sont mis en évidence en examinant leurs propriétés de propagation linéaire. Pour finir, nous nous penchons sur la condition d'accord de phase assurant l'interaction non-linéaire optimale. / The past twenty years have been exceptionally rich on the study and fabrication of nanostructured materials to control light, but no much attention was given to nonlinear optical properties of these novel materials. In this context, the present thesis would partially address this gap. In particular, we focus on the second-harmonic generation process, by considering two fundamental aspects: the second-harmonic emission control by means of nanostructured nonlinear materials and the conversion enhancement in integrated photonic devices. A novel nonlinear localization phenomenon occurring in left-handed materials and involving isotropic phase-matching is presented. We analytically demonstrate the localization process in a homogenous left-handed material and by numerical simulation we show the effect for nonlinear photonic crystals. The backward second-harmonic localization effect is used to design a second-harmonic lens. This interesting theoretical result is numerically shown for a feasible structure working at optical frequencies. The second-harmonic generation enhancement is the complementary aspect. By taking advantage of the strong light localization achieved in finite size dielectric nonlinear nanorod chains, we show that sub-wavelength transversal confinement, together with the resonant phase-matching condition, adds an important property to the second-harmonic generation enhancement. A study of linear propagation properties of nanorod chain structures first evidences its sub-wavelength guiding capabilities. Finally, the phase-matching condition that assures the maximal nonlinear interaction in this kind of structure is presented.

Dans la perspective d’un contrôle ultime de la lumière, les arrivées récentes des cristaux photoniques et des métamatériaux constituent des avancées majeures. Ces matériaux nano-structurés présentant des propriétés optiques inédites nous ouvrent tout un champ de possibilités encore inexploré. En particulier, des milieux d’indice effectif négatif sont rendus concevables. L’objectif de cette thèse est d’étudier d’un point de vue électromagnétique, à l’aide d’outils analytiques et numériques, le comportement de la lumière dans ces structures exotiques. Nous nous penchons sur les boucles de lumières, qui sont des modes localisés d’une structure multi-couches, émergeant du couplage contra-directionnel entre deux guides distincts. Une analyse physique est proposée et un modèle basé sur la théorie des modes couplés est développé. Cela nous permet de décrire avec précision l’excitation d’une boucle de lumière par une source lumineuse, et d’envisager des applications pour la mise en forme de faisceau. Dans une seconde partie, nous étudions des cristaux photoniques unidimensionnels formés par une alternance de milieux d’indices positif et négatif. Lorsque l’indice moyen est nul, une bande interdite aux propriétés nouvelles apparait. Nous montrons que le caractère dispersif des milieux transforme des pics étroits de transmission en larges bandes. Pour caractériser la propagation d’un faisceau dans un tel cristal, nous développons et validons alors un modèle qui nous permet de démontrer le potentiel en matière de mise en forme de faisceau (auto-collimation, focalisation). / In the perspective of an ultimate control of light, the recent arrivals of photonic crystals and metamaterials are major advances. These nano-structured materials with unusual optical properties are opening a whole range of possibilities still unexplored. In particular, negative index media have became conceivable. The aim of this thesis is to study, with an electromagnetic point of view, the behavior of light in these exotic structures, using analytical and numerical tools. We study the light wheels, which are localized modes of a multi-layer structure, emerging from the contra-directional coupling between two separate waveguides. A physical analysis is proposed and a model, based on the coupled mode theory, is developed. This allows us to accurately describe the excitation of a light wheel by a source, and to consider applications for beam shaping. In a second part, we study one-dimensional photonic crystals combining positive and negative index layers whose the average index is equal to zero. A band gap, called zero-n gap, appears and presents new properties that we detail. Index dispersion is shown to broaden the resonant frequencies creating then a conduction band lying inside the zero-n gap. Self-collimation and focusing effects are in addition demonstrated in zero-average index crystals supporting defect modes. This beam shaping is explained in the framework of a beam propagation model by introducing an harmonic average index parameter.

Orientador: Hugo Enrique Hernández Figueroa / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-26T15:57:35Z (GMT). No. of bitstreams: 1 ArrietaConcha_JoseLuis_M.pdf: 2860251 bytes, checksum: a9513ec6b0227b83e8ccdb097adfef27 (MD5) Previous issue date: 2014 / Resumo: Redes de comunicação ópticas são parte da sociedade de informação de hoje, em que as fibras ópticas têm um papel muito importante, uma vez que são amplamente utilizados em redes de comunicação e outros sistemas de comunicação atuais. No entanto, o uso de dispositivos eletrônicos em várias redes eletro-ópticas representam um grande engarrafamento para a utilização ideal da grande largura de banda e as taxas de dados de alta velocidade permitida por fibras ópticas. A fim de evitar tal congestionamento de tráfego da rede, dispositivos baseados em tecnologias fotônicas são uma das soluções propostas, porque eles fornecem a capacidade de manter altas velocidades de transmissão com taxas elevadas de dados e baixas perdas. Por isso, tais dispositivos fotônicos são continuamente pesquisados, a fim de melhorar a sua eficácia, a obtenção do maior confinamento e encaminhamento do sinal óptico, e melhorar a perda de inserção quando ele é integrado com outros dispositivos. Para alcançar uma maior compreensão dos dispositivos fotônicos, o trabalho apresentado aqui permite uma compreensão pedagógica e ainda completa de cristais fotônicos e efeitos magnéticos. Esta abordagem pedagógica permite uma experiência em mãos para os estudantes e pesquisadores sobre um tema complexo, um tipo de implementação experimental que normalmente exige sofisticados recursos de fabricação fotônicos. A abordagem em micro-ondas permite construir protótipos conceitualmente equivalentes e manipuláveis. Aqui, apresentamos um estudo teórico, análise numérica, modelagem de computador e simulações eletromagnéticas para um circulador de ferrita de 3 portas em uma estrutura de grade fotônico construído para a faixa de micro-ondas de 2,3GHz - 2,9GHz / Abstract: Optical communication networks are part of today¿s information based society, in which optical fibers play a very important role, since they are widely used in such communication networks and other state of the art communication systems. However, the use of electronic devices in various electronic-optical networks represent a major bottleneck for the optimal utilization of the large bandwidth and high speed data rates allowed by optical fibers. In order to avoid such congestion of network traffic, devices based on photonic technologies are one of the proposed solutions, because they provide the capability to maintain transmission speeds with both high data rates and low losses. That is why such photonic devices are continuously being researched in order to improve their effectiveness, obtain greater confinement and guiding of the optical signal, as well as to reduce the insertion loss when it is integrated with other devices. To achieve a greater understanding of photonic devices, the work presented in this paper allow for a pedagogical and yet thorough understanding of photonic crystals and magnetic effects. This pedagogical approach permits a hands-on experience for students and researchers on a complex subject, a kind of experimental implementation that usually demands sophisticated photonic fabrication resources. The microwave approach allows one to construct conceptually equivalent but hand-manipulable prototypes. Here, we present the theoretical study, numerical analysis, computer modeling and electromagnetic simulations for a 3-port ferrite circulator in a photonic grid structure built for the 2.3 GHz to 2.9 GHz microwave range. For a photonic device operating in the optical communication range, we may expect a qualitative analogous behavior / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

Les cristaux photoniques (CP) 3D sont des matériaux périodiques dont l’indice de réfraction varie périodiquement à l’échelle de la longueur d’onde. Cette propriété optique permet d’élaborer des composants optiques spécifiques comme des miroirs pour les lasers de puissance. Ces structures doivent présenter une meilleure tenue au flux laser (TFL) en régime sub-nanoseconde, comparés aux revêtements miroirs multidiélectriques actuels. Cette propriété est attendue car un unique matériau présentant une bonne TFL est utilisé pour leur élaboration, la silice. Cette étude présente donc le développement de cristaux photoniques colloïdaux 3D en utilisant la technique de Langmuir-Blodgett. Ces CP sont constitués de particules de silice avec une distribution en taille étroite, synthétisées par voie sol-gel. Différentes synthèses ont donc été développées et comparées afin d’obtenir les meilleures propriétés réfléchissantes. Une modélisation a aussi été effectuée en incluant des défauts dans une structure parfaite pour just ifier certains résultats expérimentaux. / Three-dimensional photonic crystals (PCs) are periodic materials with a modulated refractive index on a length scale close to the light wavelength. This optical property allows the preparation of specific optical components like highly reflective mirrors. Moreover, these structured materials might have a high laser-induced damage threshold (LIDT) in the sub-nanosecond range compared to multi-layered dielectric mirrors. This property is obtained because only one high LIDT material (silica) is used. In this work, we present the development of 3D PCs with narrow-sized colloidal silica particles, prepared by sol-gel process and deposited with Langmuir- Blodgett technique. Different syntheses routes have been investigated and compared regarding the optical properties of the PCs. A numerical model based on an ideal opal network including defect influence is used to explain these experimental results.

Silicon nanocrystals (SiNCs) of sizes below approximately 5 nm are a material with an efficient room-temperature photoluminescence (PL) and optical gain. Optical gain is a pre- requisite for obtaining stimulated emission from a pumped material, and the achievement of stimulated emission (and lasing) from Si-based nanostructures is of particular interest of the field of silicon photonics. The aim of this work was (i) to investigate fundamental optical properties of SiNCs, (ii) to design and prepare a photonic crystal with enhanced light ex- traction efficiency and (iii) to explore a possibility of enhancing optical gain of light-emitting SiNCs by combining them with a two-dimensional photonic crystal. First, free-standing oxide (SiOx/SiO2)-passivated SiNCs were prepared by electrochemical etching of a Si wafer. Their optical properties were studied by employing time-resolved spectroscopy, also at cryogenic temperatures. The fast blue-green emission band of these SiNCs was linked with the quasi- direct recombination of hot electrons and holes in the vicinity of the Γ-point. Furthermore, the spectral shift of the slow orange-red band (of these SiNCs) as a function of temperature was explained on the basis of an interplay between tensile strain and bulk Si temperature-induced indirect bandgap shift. The...