O presente trabalho tem como objetivo estudar a produção e caracterização de filmes finos do tipo GeO2-PbO (GP) produzidos por sputtering-RF com e sem nanopartículas (INPS) metálicas e codopados com íons de Er³+/Yb³+ para a produção de amplificadores ópticos. A incorporação dos íons de terras-raras (TR) foi verificada a partir dos espectros de emissão. Estudos relacionados ao tempo de decaimento radiativo do Er³+ também foram conduzidos. A susceptibilidade óptica não-linear de terceira ordem é reportada em 532 e 800nm. Os valores de índice de refração e absorção não-linear na presença de NPs metálicas é mais do que uma ordem de grandeza superior aos mesmos filmes sem as NPs metálicas. A produção de guias de onda do tipo rib e do tipo pedestal baseados nos filmes GP foi realizada a partir de litografia óptica seguida por processo de corrosão por plasma. A influência dos parâmetros dos processos usados em função das características dos guias também é reportada. Os guias ópticos foram caracterizados por Microscopia Eletrônica de Varredura (MEV), Microscopia de Força Atômica (AFM) e por medidas de perdas de propagação e ganho óptico. As perdas por propagação mínimas observadas foram de ~1,0dB/cm nos guias rib e de ~1,5dB/cm para os guias pedestal em 1050 nm. O ganho óptico nos guias de onda amplificadores codopados com Er³+/Yb³+ também foram obtidos. Ganhos de até 3,0dB/cm em 1530nm, sob bombeamento em 980nm foi obtido para os guias rib e de 4,0dB/cm para os guias tipo pedestal. A influência de um filme nanoestruturado de ouro depositado sobre os guias de onda foi avaliada. Aumentos na luminescência dos íons de Er³+, sob bombeamento em 980nm, de 260% na região do visível e de ~30% na região do infravermelho foram observados. O ganho óptico apresentado pelos guias rib também sofreu um aumento máximo de ~100% na presença de NPs metálicas. Guias de onda fabricados a partir da escrita por laser de femtosegundos também são estudadas em um vidro de GeO2-PbO-Ga2O3 dopadas com Er2O3. A mudança permanente do índice de refração foi obtida após o processo de escrita e guias de onda foram obtidas sob diferentes energias de pulso do laser e velocidades de varredura. O valor mínimo de perda por propagação foi de 4,8dB/cm em 1535nm. O valor de ganho óptico máximo apresentado foi de 2,7 dB/cm em 1535nm. Os resultados apresentados demonstram que guias de onda baseadas em germanatos, com ou sem NPs metálicas, são promissoras para aplicações em dispositivos fotônicos. / This work aims to study the production and characterization of GeO2-PbO (GP) thin films produced by RF-sputtering with and without metallic nanoparticles (NPs) and codoped with Er³+/Yb³+ ions for the production of optical amplifiers. The incorporation of the rare-earth ions was verified from the emission spectra. Studies related to the Er³+ radiative decay time were also performed. The third order optical nonlinear susceptibility at 532 and 800nm is reported. The nonlinear refractive index and absorption values in the presence of metallic NPs is more than one order of magnitude higher than in the films without metallic NPs. Rib and pedestal waveguides were obtained from GP thin films with optical lithography followed by reactive ion etching process. The influence of the process parameters on the waveguides characteristics is also reported. Waveguides were characterized with Scanning Electron Microscope, Atomic Force Microscope and by propagation loss and optical gain measurements. Minimum observed losses were ~1.0dB/cm for rib waveguides and ~1.5dB/cm for pedestal waveguides. Optical gain in the codoped Er³+/Yb³+ waveguide amplifiers was also obtained. The maximum optical gain in 1530nm, under 980nm pumping was 3.0dB/cm for rib waveguides and 4.0dB/cm for pedestal waveguides. The influence of a nanostructured gold thin film deposited over the waveguides was evaluated. Er³+ ions luminescence enhancement of 260% in the visible region and ~30% in the infrared region was observed, under 980 nm pumping. Optical gain was also ~100% higher in rib waveguides in the presence of gold thin film. Waveguides fabricated from direct fs laser writing are also studied, in an Er2O3 doped GeO2-PbO-Ga2O3 glass. Permanent refractive index change was obtained and waveguides were formed under different laser pulse energies and scan velocities. The minimum value of propagation loss was 4.8dB/cm at 1535nm. The sample showed a maximum optical amplification of 2.7dB/cm at 1535nm. The present results demonstrate that germanate waveguides, with or without metallic NPs are promising for applications in photonic devices.

No presente trabalho foram realizadas a síntese e caracterizações estruturais, ópticas e espectroscópicas de materiais nanocompósitos na forma de guias de onda planares e pós de (100-x)SiO2-xNb2O5 dopados com íons lantanídeos pelo método sol-gel, para aplicação em Fotônica. Foi observada separação de fase controlada e cristalização, com distribuição e tamanho de partículas, bem como a fase cristalina de Nb2O5 formada, dependentes da composição (%Nb) e temperatura de tratamento térmico. Caracterizações estruturais revelaram a formação de duas fases cristalinas de Nb2O5, ortorrômbica (fase T) e monoclínica (fase M), com distribuição de tamanhos de nanopartículas da ordem de 7 a 30 nm. Essas duas fases cristalinas apresentaram-se na forma de nanocristais dispersos em uma matriz amorfa, formando sistemas nanocompósitos transparentes. A formação dessas diferentes fases cristalinas influenciou diretamente nas propriedades luminescentes dos materiais que apresentaram uma intensa emissão na região do Infravermelho próximo (com máximo de emissão em 1530 nm) sob excitação em 980 nm, com valores de largura de banda variando de 48 a 84 nm. A dependência dos espectros de emissão (largura inomogênea e componentes Stark), valores de largura de banda e tempos de vida do estado excitado 4I13/2 em relação às diferentes fases cristalinas de Nb2O5 formadas, permitiram a conclusão de que os íons Er3+ estão ocupando preferencialmente ambientes de baixa energia de fônon à base de Nb2O5. Estudos espectroscópicos dos nanocompósitos dopados com íons Eu3+ possibilitaram maiores evidências da ocupação dos íons lantanídeos em diferentes sítios de simetria no Nb2O5. A co-dopagem dos nanocompósitos com íons Er3+ e Yb3+ permitiu uma intensificação na emissão na região do Infravermelho próximo, correspondente à transição 4I13/24I15/2, decorrente da maior seção de choque dos íons Yb3+ em 980 nm e um processo eficiente de transferência de energia entre os íons Yb3+ e os íons Er3+ distribuídos nas matrizes estudadas. Essa transferência de energia eficiente intensificou também as emissões tanto na região do verde como do vermelho, decorrente de processos de conversão ascendente. Um estudo detalhado da dinâmica do processo de conversão ascendente foi realizado para os pós e guias de onda. No presente trabalho também foram obtidos guias de onda planares (100-x)SiO2-xNb2O5 dopados com íons Er3+ e co-dopados com íons Er3+ e Yb3+, com excelentes propriedades estruturais, morfológicas, ópticas e espectroscópicas para aplicação como amplificadores ópticos, tais como, superfícies livres de trinca, distribuição uniforme dos valores de índice de refração através da superfície e em função da profundidade, baixa rugosidade, alta porcentagem de confinamento da luz, uma excelente transparência das matrizes no visível e infravermelho próximo, bem como emissão em região usada para transmissão de sinal óptico em telecomunicações. Os guias de onda apresentaram intensas emissões tanto na região do Infravermelho próximo quanto no visível, decorrente de processos de conversão ascendente, apresentando ainda uma interessante variação das cores verde e vermelha, dependendo-se da potência de excitação utilizada e da proporção em mol (%) de Nb adicionada. Após a constatação dos excelentes resultados obtidos nos guias dopados com íons Er3+ e Yb3+, foram preparados nanocompósitos co-dopados com Tm3+ e Yb3+ na forma de pós e guias de onda planares, que apresentaram uma largura de banda de 120 nm na região do infravermelho próximo (com máximo de emissão em 1650 nm) e emissões na região do azul (475 nm) e no infravermelho (785 nm), decorrentes de processos de conversão ascendente. Por fim, foi realizada inscrição bem sucedida de canais nos guias de onda planares utilizando um laser de Ti:safira de femtosegundos. Em suma, os materiais nanocompósitos (100-x)SiO2-xNb2O5 apresentam um grande potencial de aplicação, especialmente em fotônica como amplificadores ópticos (EDWA) em telecomunicações, em circuitos fotônicos, lasers na região do visível (explorando conversão ascendente de energia), marcadores ópticos, dependendo fundamentalmente dos íons lantanídeos utilizados na dopagem. No caso especifico de amplificadores ópticos para telecomunicações, pôde-se concluir que as propriedades mais adequadas foram observadas nos materiais nanocompósitos (100-x)SiO2-xNb2O5 guias de onda planares contendo as proporções 80Si-20Nb e 70Si-30Nb tratados termicamente a 900oC co-dopados com íons Er3+/Yb3+ e Tm3+/Yb3+ / In the present work are reported the synthesis and structural, optical and spectroscopic characterizations of lanthanide doped (100-x)SiO2-xNb2O5 nanocomposites materials as planar waveguides and powders prepared by the sol gel method for photonic applications. The controlled phase separation and crystallization observed, as well as the particle size and distribution depended on the composition (%Nb) and the annealing temperature. The structural characterization revealed the formation of two Nb2O5 crystalline phases, orthorhombic (T-phase) and monoclinic (M-phase), with nanoparticle size distribution from 7 to 30 nm. The two crystalline phases were observed as nanocrystals dispersed in an amorphous matrix, constituting transparent nanocomposite systems. The formation of the different crystalline phases affected directly the materials luminescent properties which showed an intense near infrared emission (with maximum peak at 1530 nm) under 980 nm excitation, with bandwidth values from 48 to 84 nm. The dependence of emission spectra (inhomogeneous broadening and Stark components), the bandwidth values and the 4I13/2 excited state lifetimes dependence upon the different Nb2O5 crystalline phases formation, led to the Er3+ ions preferential occupation on low phonon energy, Nb2O5-rich environment. Spectroscopic studies with Eu3+-doped nanocomposites provided additional evidences of the lanthanide occupation of different symmetry sites on the Nb2O5-rich environment. The nanocomposites co-doping with Er3+ and Yb3+ ions allowed intensification on the near infrared emission, corresponding to the 4I13/24I15/2 transition, which resulted from the higher cross section of Yb3+ ions at 980 nm and an efficient energy transfer process between the Yb3+ ions and the Er3+ ions. This efficient energy transfer process also intensified the emissions both in green and red range, deriving from upconversion processes. A detailed study on the upconversion processes was made for nanocomposites and waveguides. In the present work, Er3+-doped and Er3+ and Yb3+ co-doped planar waveguides (100-x)SiO2-xNb2O5 with excellent optical, morphological and spectroscopic properties were also obtained, such as, crack free surfaces, a uniform refractive index profile across the surface and the thickness, low rugosity, high light confinement, low optical losses, and an excellent infrared and visible range matrix transparency, as well as emission used on optical telecommunication transmission. The waveguides showed emission both on near infrared and visible range, resulting from upconversion processes, showing an interesting color tuning phenomena in the green and red ranges, dependent on the excitation power and Nb content (mol%). After the excellent results verified with Er3+ and Yb3+, Tm3+ and Yb3+ co-doped nanocomposites and planar waveguides were prepared, which showed a bandwidth of 120 nm in the infrared range (with maximum peak at 1650 nm) and blue (475 nm) and near infrared (785 nm) emissions deriving from upconversion processes. Finally, channel writing using a femtosecond Ti:sapphire laser was successfully performed on the planar waveguides. Therefore, the (100-x)SiO2-xNb2O5 nanocomposite materials have shown great potential application, especially in photonic, such as, optical amplifiers (EDWA), photonic circuits, visible range lasers (exploring upconversion processes), and optical markers, depending on the lanthanide doping. In the specific case of optical amplifiers for telecommunication application, it could be concluded that the most adequate properties were observed on the ions Er3+/Yb3+ and Tm3+/Yb3+ co-doped (100-x)SiO2-xNb2O5 nanocomposites at 80Si-20Nb and 70Si-30Nb ratios, annealed at 900°C

O presente trabalho tem como objetivo estudar a produção e caracterização de filmes finos do tipo GeO2-PbO (GP) produzidos por sputtering-RF com e sem nanopartículas (INPS) metálicas e codopados com íons de Er³+/Yb³+ para a produção de amplificadores ópticos. A incorporação dos íons de terras-raras (TR) foi verificada a partir dos espectros de emissão. Estudos relacionados ao tempo de decaimento radiativo do Er³+ também foram conduzidos. A susceptibilidade óptica não-linear de terceira ordem é reportada em 532 e 800nm. Os valores de índice de refração e absorção não-linear na presença de NPs metálicas é mais do que uma ordem de grandeza superior aos mesmos filmes sem as NPs metálicas. A produção de guias de onda do tipo rib e do tipo pedestal baseados nos filmes GP foi realizada a partir de litografia óptica seguida por processo de corrosão por plasma. A influência dos parâmetros dos processos usados em função das características dos guias também é reportada. Os guias ópticos foram caracterizados por Microscopia Eletrônica de Varredura (MEV), Microscopia de Força Atômica (AFM) e por medidas de perdas de propagação e ganho óptico. As perdas por propagação mínimas observadas foram de ~1,0dB/cm nos guias rib e de ~1,5dB/cm para os guias pedestal em 1050 nm. O ganho óptico nos guias de onda amplificadores codopados com Er³+/Yb³+ também foram obtidos. Ganhos de até 3,0dB/cm em 1530nm, sob bombeamento em 980nm foi obtido para os guias rib e de 4,0dB/cm para os guias tipo pedestal. A influência de um filme nanoestruturado de ouro depositado sobre os guias de onda foi avaliada. Aumentos na luminescência dos íons de Er³+, sob bombeamento em 980nm, de 260% na região do visível e de ~30% na região do infravermelho foram observados. O ganho óptico apresentado pelos guias rib também sofreu um aumento máximo de ~100% na presença de NPs metálicas. Guias de onda fabricados a partir da escrita por laser de femtosegundos também são estudadas em um vidro de GeO2-PbO-Ga2O3 dopadas com Er2O3. A mudança permanente do índice de refração foi obtida após o processo de escrita e guias de onda foram obtidas sob diferentes energias de pulso do laser e velocidades de varredura. O valor mínimo de perda por propagação foi de 4,8dB/cm em 1535nm. O valor de ganho óptico máximo apresentado foi de 2,7 dB/cm em 1535nm. Os resultados apresentados demonstram que guias de onda baseadas em germanatos, com ou sem NPs metálicas, são promissoras para aplicações em dispositivos fotônicos. / This work aims to study the production and characterization of GeO2-PbO (GP) thin films produced by RF-sputtering with and without metallic nanoparticles (NPs) and codoped with Er³+/Yb³+ ions for the production of optical amplifiers. The incorporation of the rare-earth ions was verified from the emission spectra. Studies related to the Er³+ radiative decay time were also performed. The third order optical nonlinear susceptibility at 532 and 800nm is reported. The nonlinear refractive index and absorption values in the presence of metallic NPs is more than one order of magnitude higher than in the films without metallic NPs. Rib and pedestal waveguides were obtained from GP thin films with optical lithography followed by reactive ion etching process. The influence of the process parameters on the waveguides characteristics is also reported. Waveguides were characterized with Scanning Electron Microscope, Atomic Force Microscope and by propagation loss and optical gain measurements. Minimum observed losses were ~1.0dB/cm for rib waveguides and ~1.5dB/cm for pedestal waveguides. Optical gain in the codoped Er³+/Yb³+ waveguide amplifiers was also obtained. The maximum optical gain in 1530nm, under 980nm pumping was 3.0dB/cm for rib waveguides and 4.0dB/cm for pedestal waveguides. The influence of a nanostructured gold thin film deposited over the waveguides was evaluated. Er³+ ions luminescence enhancement of 260% in the visible region and ~30% in the infrared region was observed, under 980 nm pumping. Optical gain was also ~100% higher in rib waveguides in the presence of gold thin film. Waveguides fabricated from direct fs laser writing are also studied, in an Er2O3 doped GeO2-PbO-Ga2O3 glass. Permanent refractive index change was obtained and waveguides were formed under different laser pulse energies and scan velocities. The minimum value of propagation loss was 4.8dB/cm at 1535nm. The sample showed a maximum optical amplification of 2.7dB/cm at 1535nm. The present results demonstrate that germanate waveguides, with or without metallic NPs are promising for applications in photonic devices.

Cette thèse est une contribution au domaine de recherche de la plasmonique nonlinéaire, domaine émergent de l'optique. L'objectif principal est de démontrer expérimentalement l'autofocalisation d'une onde plasmonique.L'étude débute avec la fabrication et la caractérisation de guides plans en verre de chalcogénure de composition Ge-Sb-Se. Une technique basée sur la formation de solitons spatiaux est développée afin d’estimer leurs non-linéarités Kerr. Les propriétés optiques linéaires et non linéaires de ces guides sont étudiées aux longueurs d’onde de 1200 nm et 1550 nm.Des structures plasmoniques sont ensuite conçues pour propager des ondes hybrides plasmon-solitons avec des pertes de propagation modérées. Elles sont constituées des guides précédents recouverts de nanocouches de silice et d'or.Les caractérisations optiques par couplage plasmon-soliton révèlent une forte autofocalisation subie par l’onde qui se propage à l'intérieur de la structure plasmonique. Comme prévu par la théorie, le comportement est présent uniquement pour une lumière polarisée TM. Des résultats expérimentaux détaillés de cette autofocalisation exaltée par effet plasmonique sont présentés pour différentes configurations. Des simulations confirment les résultats expérimentaux obtenus.Cette démonstration fondamentale vient confirmer le concept d’autofocalisation assistée par plasmon tout en révélant un effet nonlinéaire très efficace. Cela ouvre de nouvelles perspectives pour le développement de dispositifs photoniques non linéaires intégrés ainsi que de nouveaux phénomènes physiques. / This dissertation contributes to the research area of nonlinear plasmonics an emerging field of optics. The main goal is to demonstrate experimentally the spatial self-trapping of a plasmonic wave.The study begins with the fabrication and the characterization of slab Ge-Sb-Se chalcogenide waveguides. A technique based on the formation of spatial solitons is developed to estimate their Kerr nonlinearities. Linear and nonlinear optical properties of the waveguides are studied at the wavelengths of 1200 nm and 1550 nm.Plasmonic structures are then designed to propagate hybrid plasmon-soliton waves with moderate propagation losses. They are constituted of the previous waveguides covered with nanolayers of silica and gold.Optical characterizations reveal a giant self-focusing undergone by the wave that propagates inside the plasmonic structure. The behavior is present only for TM polarized light as expected from theory. Detailed experimental results of this plasmon enhanced nonlinear self-trapping corresponding to different configurations are presented. Simulations confirm the obtained experimental results.This fundamental demonstration confirms the concept of plasmon-assisted self-focusing while revealing a very efficient nonlinear effect. This opens new perspectives for the development of integrated nonlinear photonic devices as well as new physical phenomena.

Le projet de thèse est divisé en deux parties. D’une part, la génération directionnelle et singulière de plasmons de surface (SPPs) par des ouvertures nanométriques a été réalisé et optimisé par le biais de microscopie de fuites radiatives (LRM). Nous démontrons expéri- mentalement qu’une structure plasmonique composée de nano-ouvertures en forme de T et Λ permet de contrôler le couplage unidirectionnel et radialdes SPPs grâce au spin de la lumière incidente. Pour confirmer nos résultats expérimentaux, nous développons un modèle analytique qui décrit les coupleurs plasmoniques constitués de nano-ouvertures par représentation multidipolaire, permettant ainsi une explication théorique de la directionalité et de la formation de vortex plasmonique. L’optimisation des paramètres géométriques tels que l’angle au sommet des ouvertures en forme de Λ montre la possibilité de maximiser la directivité et le taux d’extinction à la fois pour le couplage directionnel et la génération des vortex dans le champ lointain. Parailleurs, notre méthode basée sur la détection LRM, permet une analyse quantitative et est avérée être une technique de caractérisation sophistiquée pour cartographier le champ plasmonique. Il fournit également plusieurs nouvelles possibilités pour la focalisation de SPP contrôlée en polarisation.D’autre part,le couplage spin-orbite de la lumière dans un guide et son effet réciproque sont réalisées et confirmées expérimentalement et théoriquement. Les coupleurs et découpleurs réseaux sur le guide d’ondes sont d’abord développés et étudiés. La sortie parfaite de la lumière confinée par le découpleur nous offre la possibilité de détecter les ondes guidées. La fluorescence des nanocristaux déposés sur la surface de l’échantillon montre une autre possibilité de visualiser directement la propagation de la lumière dans le guide d’onde. Le couplage directionnel contrôlé par spin est réalisé par des antennes en forme de Λ et est confirmé par des images en champ sombre avec des découpleurs et des images de fluorescence. En outre, l’effet réciproque est observé avec une imperfection de polarisation de sortie qui est expliqué théoriquement par le fait que les ordres de diffraction par les antennes en forme de Λ influent sur les états de polarisation finaux. Ainsi, l’effet réciproque est parfaitement réalisé par la sélection d’une région spécifique de diffraction dans le plan de Fourier. La caractérisation quantitative des interactions spin-orbite nous permet d’envisager le développement de nouveaux coupleurs directionnels dans le domaine de la nanophotonique tels que le traitement quantique de l’information. / In this project, two contributions are reported. Firstly, the directional and singular generation of Surface Plasmon Polaritons (SPPs) in the nanoapertures is investigated using the Leakage Radiation Microscopy (LRM). We demonstrate experimentally spin-driven directional coupling as well as singularity (inward) and vortex (outward radial coupling) of SPPs by nanostructures built with T-shaped and Λ-shaped apertures.To support our experimental findings, we develop an analytical model based on a multidipolar representation of Λ- andT-shaped aperture plasmonic couplers, allowing a theoretical explanation of both directionality and singular SPP formation. The optimal apex angle of Λ-shaped apertures shows the possibility to maximize the directiviy and extinction ratio for both directional coupling and singular SPP generation in the far field. Besides, our method based on LRM detection, allows quantitative analysis and is proven to be a sophisticated characterization technique for mapping the SPP vortex field.It also provides several new possibilities for polarization-controlled SPP sub-wavelength focusing.Secondly, the spin-orbit coupling of light into a photonic waveguide and its reciprocal effect are realized and confirmed both experimentally and theoretically. Coupler and decoupler gratings on the waveguide are firstly developed and investigated. The radiation of the confined light from the decoupler provides us a possibility to detect the guided waves. The fluorescence of nanocrystals deposited on the sample surface shows another possibility to directly visualize the light propagation in the waveguide. The spin-driven directional coupling is achieved by Λ-shaped antennas and is certified by the dark field images with decouplers and the fluorescence images. Furthermore, the reverse effect is observed with an imperfection of output polarization which is explained that the diffraction orders by the Λ-shaped apertures influence the final polarization states based on an analytical model. Thus, the reciprocal effect is realized by selecting the specific diffraction region on the Fourier plane. We believe that the quantitative characterization of spin-orbit interactions will pave the way for developing new directional couplers in the field of nanophotonics such as quantum information processing and so forth.

Many new applications are being proposed and developed for use in the terahertz (THz) frequency region. Similarly, many new materials are being characterized for possible use in this area. Nanostructured forms are of particular interest since they may yield desirable properties, but they remain especially challenging to characterize. This work focuses on the characterization of zinc oxide (ZnO) in bulk and nanowire form. A method for characterizing nanostructures at THz by use of a parallel-plate waveguide (PPWG) is presented. This method is novel in that it is simple, both in theory and practice, and does not require the use of complex measurement techniques such as differential and double modulated terahertz time-domain spectroscopy (THz-TDS). To enable easy evaluation of the quality of the result the maximum deviation in the material response measurement is presented. The dielectric properties of bulk and nanowire ZnO as determined by THz-TDS measurements are reported, and the electrical conductivity extracted from both are presented for comparison. Experimental results are compared to the well established pseudo-harmonic phonon dielectric model. Shortcomings in the pseudo-harmonic phonon model are resolved when coupled with a modified Drude model. This work will enable the determination of THz material properties from nano-scale and very-thin film materials with better reliability and practicality than what has been possible until now.

Kunststofflichtwellenleiter (POFs) stellen ein verhältnismäßig neues Medium zur optische Datenkommunikation über kurzen Strecken dar. Während ihrer Einsatzdauer unterliegen POFs unterschiedlichen Arten von Umweltbeanspruchungen, hauptsächlich durch hohe Temperatur, hohe Feuchtigkeit und mechanischen Belastungen. Zahlreiche experimentelle Forschungen beschäftigten sich mit der standardisierten Prüfung der Zuverlässigkeit von im Handel erhältlichen Fasern. Jedoch gab es bisher wenig Erfolg bei der Bemühung, zwei grundlegende optische Erscheinungen, Absorption und Streuung, die die Lichtausbreitung in Fasern stark beeinflussen, zu verstehen und praktisch zu modellieren: Diese beiden Effekte beschreiben nicht nur die Qualität neuer Fasern, sondern sie werden auch stark durch die Alterungsprozess beeinflusst.<br><br> Der Hauptzweck dieser Doktorarbeit war es, ein praktisch verwendbares und theoretisch gut fundiertes Modell der Lichtausbreitung in nicht gealterten und gealterten POFs zu entwickeln und es durch optische Experimente zu verifizieren. Dabei wurden anwendungsorientierte Aspekte mit theoretischer POF-Modellierung kombiniert. Die Arbeit enthält die erste bekannte Anwendung der Wellenanalyse zur Untersuchung der winkelabhängigen Eigenschaften der Streuung in Lichtwellenleitern.<br><br> Für die praktischen Experimente wurden mehrere POF-Proben unterschiedlicher Hersteller künstlich gealtert, indem sie bis 4500 Stunden bei 100 °C gelagert wurden (ohne Feuchtekontrolle). Die Parameter der jeweiligen Simulationen wurden mittels einer systematischen Optimierung an die gemessen optischen Eigenschaften der gealterten Proben angeglichen. Die Resultate deuten an, dass der Übertragungsverlust der gealterten Fasern in den ersten Tagen und Wochen der Alterung am stärksten durch eine wesentliche physikalische Verschlechterung der Kern-Mantel-Grenzfläche verursacht wird. Chemische Effekte des Alterungsprozesses scheinen im Faserkernmaterial zuerst nach einigen Monaten aufzutreten. / This thesis discusses theoretical and practical aspects of modelling of light propagation in non-aged and aged step-index polymer optical fibres (POFs). Special attention has been paid in describing optical characteristics of non-ideal fibres, scattering and attenuation, and in combining application-oriented and theoretical approaches. The precedence has been given to practical issues, but much effort has been also spent on the theoretical analysis of basic mechanisms governing light propagation in cylindrical waveguides.<br><br>As a result a practically usable general POF model based on the raytracing approach has been developed and implemented. A systematic numerical optimisation of its parameters has been performed to obtain the best fit between simulated and measured optical characteristics of numerous non-aged and aged fibre samples. The model was verified by providing good agreement, especially for the non-aged fibres. The relations found between aging time and optimal values of model parameters contribute to a better understanding of the aging mechanisms of POFs.

Kunststofflichtwellenleiter (POFs) stellen ein verhältnismäßig neues Medium zur optische Datenkommunikation über kurzen Strecken dar. Während ihrer Einsatzdauer unterliegen POFs unterschiedlichen Arten von Umweltbeanspruchungen, hauptsächlich durch hohe Temperatur, hohe Feuchtigkeit und mechanischen Belastungen. Zahlreiche experimentelle Forschungen beschäftigten sich mit der standardisierten Prüfung der Zuverlässigkeit von im Handel erhältlichen Fasern. Jedoch gab es bisher wenig Erfolg bei der Bemühung, zwei grundlegende optische Erscheinungen, Absorption und Streuung, die die Lichtausbreitung in Fasern stark beeinflussen, zu verstehen und praktisch zu modellieren: Diese beiden Effekte beschreiben nicht nur die Qualität neuer Fasern, sondern sie werden auch stark durch die Alterungsprozess beeinflusst. <br><br> Der Hauptzweck dieser Doktorarbeit war es, ein praktisch verwendbares und theoretisch gut fundiertes Modell der Lichtausbreitung in nicht gealterten und gealterten POFs zu entwickeln und es durch optische Experimente zu verifizieren. Dabei wurden anwendungsorientierte Aspekte mit theoretischer POF-Modellierung kombiniert. Die Arbeit enthält die erste bekannte Anwendung der Wellenanalyse zur Untersuchung der winkelabhängigen Eigenschaften der Streuung in Lichtwellenleitern. <br><br> Für die praktischen Experimente wurden mehrere POF-Proben unterschiedlicher Hersteller künstlich gealtert, indem sie bis 4500 Stunden bei 100 °C gelagert wurden (ohne Feuchtekontrolle). Die Parameter der jeweiligen Simulationen wurden mittels einer systematischen Optimierung an die gemessen optischen Eigenschaften der gealterten Proben angeglichen. Die Resultate deuten an, dass der Übertragungsverlust der gealterten Fasern in den ersten Tagen und Wochen der Alterung am stärksten durch eine wesentliche physikalische Verschlechterung der Kern-Mantel-Grenzfläche verursacht wird. Chemische Effekte des Alterungsprozesses scheinen im Faserkernmaterial zuerst nach einigen Monaten aufzutreten. / This thesis discusses theoretical and practical aspects of modelling of light propagation in non-aged and aged step-index polymer optical fibres (POFs). Special attention has been paid in describing optical characteristics of non-ideal fibres, scattering and attenuation, and in combining application-oriented and theoretical approaches. The precedence has been given to practical issues, but much effort has been also spent on the theoretical analysis of basic mechanisms governing light propagation in cylindrical waveguides. <br><br> As a result a practically usable general POF model based on the raytracing approach has been developed and implemented. A systematic numerical optimisation of its parameters has been performed to obtain the best fit between simulated and measured optical characteristics of numerous non-aged and aged fibre samples. The model was verified by providing good agreement, especially for the non-aged fibres. The relations found between aging time and optimal values of model parameters contribute to a better understanding of the aging mechanisms of POFs.<br><br>

The mid-infrared (MIR) spectral range (2-20 m) is particularly useful for chemical sensing due to the excitation of fundamental rotational and vibrational modes. In the fingerprint region (10-20 m), most organic analytes have unique absorption patterns; absorption measurements in this region provide molecule-specific information with high sensitivity. Quantum cascade lasers (QCLs) present an ideal light source for (MIR) chemical sensing due to their narrow linewidth, high spectral density, compact size, and ease of fabrication of nearly any MIR wavelength. As the emission wavelength is dependent on layer size within the heterostructure rather than material composition, various wavelengths in the MIR can be achieved through bandstructure engineering. High sensitivity measurements have been achieved in both gas and liquid phase by developing integrated sensing systems. The laser emission frequency is selected to match a strong absorption feature for the analyte of interest where no other interfering bands are located. A waveguide is then developed to fit the application and wavelength used. Gas sensing applications incorporate silica hollow waveguides (HWG) and an OmniGuide fiber (or photonic bandgap HWG). Analyte gas is injected into the hollow core allowing the HWG or OmniGuide to serve simultaneously as a waveguide and miniaturized gas cell. Sensitivities of parts per billion are achieved with a response time of 8 s and a sample volume of approximately 1 mL. Liquid sensing is achieved via evanescent wave measurements with planar waveguides of silver halide (AgX) and gallium arsenide (GaAs). GaAs waveguides developed in this work have a thickness on the order of the wavelength of light achieving single-mode waveguides, providing a significant improvement in evanescent field strength over conventional multimode fibers. Liquid samples of L volume at the waveguide surfaces are detected. QCLs have begun to be utilized as a light source in the MIR regime over the last decade. The next step in this field is the development of compact and highly integrated device platforms which take full advantage of this technology. The sensing demonstrations in this work advance the field towards finding key applications in medical, biological, environmental, and atmospheric measurements.

The incorporation of porosity in a material potentially results in the changes in electrical, mechanical and electrical properties and has generated much interest by researchers. The development of new techniques for inducing porosity in thin films may prove advantageous if they lead to a decrease in processing complexity, or an increase in the processing flexibility by widening the window of compatible physical conditions, or the improvement of the final properties of the porous materials. Two processing techniques were developed to produce porosity in thin dielectric films at temperatures below the glass transition temperature of the host matrix. These glassy-regime processing methods relied on the susceptibility of hydrogen silsesquioxane (HSQ) to gelation in the glassy regime when exposed to polar substances. Both of these glassy-regime processing methods relied on the susceptibility of hydrogen silsesquioxane (HSQ) towards gelation in the glassy regime when exposed to polar substances. The first processing method made use of co-solvent mixtures of polar non-protic organic solvent to serve both as gelation catalysts and pore-generators. HSQ films were soaked in the polar organic co-solvents, which penetrated the films and initiated crosslinking throughout the matrix. Afterwards the films were baked, volatilizing entrapped solvents and producing air pockets within the rigid matrix. The second porosity method used UV-radiation to initiate acid-catalyzed decomposition of polycarbonate sacrificial polymers after first using bases to catalyze the gelation of HSQ. The radiation-based (direct-write) decomposition of the porogen enabled the selective patterning of regions porosity via the use of a photomask, which resulted in the creation of refractive index profiles in the direct-written films. Porous films that were produced by these two glassy-state processing techniques were used to build slab waveguide structures. Optical characterization experiments showed that the fabricated waveguides had average propagation losses of 16 - 27 dB/cm for the first guided TE mode and about 36-40 dB/cm, for the second TE guided mode. It is believed that the large propagation loss values were caused by a combination of the Rayleigh scattering from the relatively large UV-induced pores produced in the direct-write layers as well as scattering induced by surface roughness.