This thesis is concerned with the development and application of laser induced thermal grating spectroscopy (LITGS) as a tool for thermometry in reacting and non-reacting flows. LITGS signals, which require resonant excitation of an absorbing species in the measurement region to produce a thermal grating, are acquired for systematic measurements of temperature in high pressure flames using OH and NO as target absorbing species in the burned gas. The signal obtained in LITGS measurements appears in the form of a time-based signal with a characteristic frequency proportional to the value or the sound speed of the local medium. With knowledge of the gas composition, the temperature can be derived from the speed of sound measurement. LITGS thermometry using resonant excitation of OH in the burned gas region of in oxygen enriched CH4/O2/N2 and CH4/air laminar flames was performed at elevated pressure (0.5 MPa) for a range of conditions. Measurements were acquired in oxygen enriched flames to provide an environment in which to demonstrate LITGS thermometry under high temperature conditions (up to 2900 K). The primary parameters that influence the quality of LITGS signal were also investigated. The signal contrast, which acts as a marker for the strength of the frequency oscillations, is shown to increase with an increase in the burnt gas density at the measurement point. LITGS employing resonant excitation of NO is also demonstrated for quantitative measurements of temperature in three environments – a static pressure cell at ambient temperature, a non-reacting heated jet at ambient pressure and a laminar premixed CH4/NH3/air flame operating at 0.5 MPa. Flame temperature measurements were acquired at various locations in the burned gas close to a water-cooled stagnation plate, demonstrating the capability of NO-LITGS thermometry for measuring the spatial distribution of temperature in combustion environments. In addition, the parameters that in influence the local temperature rise due to LITGS were also investigated in continuous vapour flows of acetone/air and toluene/air mixtures at atmospheric conditions. Acetone and toluene are commonly targeted species in previous LITGS measurements due to their favourable absorption characteristics. Results indicate that LITGS has the potential to produce accurate and precise measurements of temperature in non-reacting flows, but that the product of the pump intensity at the probe volume and the absorber concentration must remain relatively low to avoid significant localised heating of the measurement region.

[pt] As redes ópticas passivas de nova geração 2 (NG-PON2) estão estudando e considerando o WDM-PON (Wavelength-Division-Multiplexed Passive Optical Networks) como a nova arquitetura para as redes de acesso, é provável que esta arquitetura seja adotada num futuro como o padrão. No entanto, algumas instalações já foram realizadas em todo o mundo, a maior parte delas na Coréia do Sul. Com o objetivo de reduzir os custos de operação (OPEX) e garantir a qualidade do serviço (QoS) um sistema de supervisão e localização de falhas é necessário. Neste trabalho é proposto e demonstrado um OTDR sintonizável (Optical Time-Domain Reflectometer) para realizar o monitoramento de redes WDMPON em serviço. O método apresentado é provado para diferentes fontes laser sintonizáveis CW (Continuous Wave) e utiliza um amplificador óptico semicondutor (SOA) como comutador para o sinal de prova. O sistema de monitoramento é provado experimentalmente numa rede WDM-PON simulada no laboratório a qual utiliza um AWG (Arrayed Waveguide Grating) como distribuidor. Os resultados foram melhorados utilizando diferentes métodos para mitigar os efeitos de interferência. / [en] The Next Generation Passive Optical Network 2 (NG-PON2) is considering and studying wavelength-division-multiplexed passive optical networks (WDM-PONs) as the new architecture for access networks, this architecture is likely to be adopted in near future as standard. However some deployments have been achieved worldwide, most of them in South Korea. In order to lower the operational expenditure (OPEX) and guarantee quality-of-service (QoS) an in-service monitoring and fault localization system is required. We propose and demonstrate a tunable optical time-domain reflectometer (T-OTDR) for in-service monitoring of (WDM-PONs). The proposed method is proved for different continuous wave tunable laser sources (CW TLS), and uses semiconductor optical amplifier (SOA) as a switch for the probe signal. This monitoring system is experimentally proved in a simulated WDMPON employing a cyclic AWG (Arrayed Waveguide Grating) as wavelength distributor. We improve the results using different methods to mitigate the interference effects.

Le sujet de cette thèse est l'interférométrie X à réseaux: une technique d’imagerie développée pour la première fois il y a quelques années et qui donne des images de phase et de diffusion (small angle X-ray scattering) de haute sensibilité. Cette technique a un potentiel considérable pour la visualisation du structures qui absorbent faiblement les rayons X, et pour la détection de détails plus petits que la résolution du détecteur, par exemple les fissures et les fibres. Des structures de ce type ne peuvent pas être visualisées avec l’imagerie conventionnelle à rayons X en absorption. Dans le cadre des travaux sur cette thèse, un interféromètre à réseau à rayons X pour radiographie et tomographie multimodale a été installé à la ligne de lumière ID19 de l‘European Synchrotron Radiation Facility à Grenoble, France. L’excellente performance de cet instrument a été démontrée sur une grande variété d'échantillons de tissus biologiques mous, sur des échantillons paléontologiques, et sur des tissus osseux. Une autre partie des ce travail porte sur des améliorations de la technique d’imagerie elle-même. La première des ces améliorations consiste en un développement de méthodes avancées pour la tomographie avec réseaux. Ces méthodes peuvent réduire considérablement la dose livrée à l’échantillon durant les mesures nécessaires pour la reconstruction tomographique tout en préservant la qualité d’image. Un autre résultat majeur dans le cadre de ce travail est la conception, la mise en oeuvre et la démonstration d’un interféromètre à réseau à deux dimensions (2D). Cet appareil utilise des réseaux bidimentionnels au lieu de réseaux linéaires. L’interféromètre 2D produit des cartes d'angles de réfraction et des images de type champ sombre dans plusieurs directions du plan d’image et améliore considérablement la qualité des radiographies à réseau. Le champ d’application de l’interféromètre 2D n’est pas limité à l'imagerie par rayons X, puisque le nouveau dispositif peut aussi être particulièrement utile pour la caractérisation de composantes optiques de haute précision, tel que démontré par des expériences de métrologie à la longueur d'onde d'utilisationsur des lentilles réfractives pour rayons X. / The subject of this thesis is X-ray grating interferometry: an imaging technique first demonstrated a few years ago, which yields high-sensitivity phase and dark-field (small angle X-ray scattering) images of the investigated specimen. It bears tremendous potential for the visualization of low-absorbing features, and for the detection of details smaller than the resolution of the imaging system, such as cracks and fibers. Structures of this type cannot be visualized with conventional absorption X-ray imaging. As a part of this thesis work, an X-ray grating interferometer for multimodal radiography and tomography was installed at the beamline ID19 of the European Synchrotron Radiation Facility in Grenoble, France. The excellent performance of this instrument has been demonstrated on a large variety of soft-tissue biological samples, on paleontological specimens, and on osseous tissues. Another part of the present work concerns improvements of the imaging technique itself. The first of these improvements consists in the development of advanced schemes for grating-based tomography. These schemes can substantially reduce the dose delivered to the sample during a grating-based tomography scan, while preserving the image quality. Another major achievement of this thesis is the design, implementation and demonstration of a two-dimensional (2D) grating interferometer. This device uses gratings structured in two dimensions rather than line gratings. The 2D interferometer gives refraction angle and dark-field signals in multiple directions of the image plane and significantly improves the quality of the grating-based radiographies. The application range of the 2D interferometer is not restricted to X-ray imaging; the new device may also be particularly useful for high-precision optics characterization, as is shown by in-situ at-wavelength investigations of X-ray refractive lenses.

[pt] O aumento dos custos relacionados aos processos de manutenção em estruturas como aeronaves, aliadas à crescente demanda das mesmas, alimentam a necessidade de investimentos em técnicas inovadoras de monitoramento estrutural. Dessa forma, o trabalho realizado nesta tese, busca o desenvolvimento de uma técnica de monitoramento ativo, visando o acompanhamento de parâmetros da estrutura analisada, a fim de identificar e caracterizar processos de dano não visíveis, tais como corrosão e delaminação. A metodologia empregada, teve como base a análise dos padrões de deformação superficial, obtidos com o uso de grades de sensores à fibra óptica baseadas em redes de Bragg (FBG). Inicialmente, tais padrões foram provocados por carregamentos estáticos (tração), e posteriormente por atuadores PTZ fixados à estrutura. Estes últimos são submetidos a uma voltagem alternada e frequência fixa. Esta técnica apresenta todas as vantagens dos sensores FBG (massa e dimensões reduzidas, imunidade eletromagnética, elevado poder de multiplexação e alta sensibilidade entre outras), alem de permitir a visualização de alterações nos padrões de deformação, provocados por danos, através da variação da frequência de excitação. Com relação à interpretação dos resultados, a estratégia empregada consistiu em separar o problema de detecção e caracterização dos danos. Dessa forma, a detecção é realizada comparando a energia das deformações superficiais dos corpos de prova nos casos com e sem defeito, enquanto a caracterização é obtida através a utilização de redes neurais artificiais (RNA), por meio de rotinas de reconhecimento de padrões. / [en] The higher costs related to maintenance processes in structures such as aircraft, coupled with the growing demand of them, fueling the need for investment in innovative techniques for structural monitoring. Thus, the work done in this thesis seeks to develop a technique of active monitoring, aiming at monitoring of structure parameters analyzed in order to identify and characterize processes of hidden damage such as corrosion and delamination. The maid methodology was based on the analysis of patterns of surface deformation, obtained with the use of nets of optical fiber sensors based on fiber Bragg gratings ( FBG ). Initially, these patterns were caused by static loads (tension ), and later by PTZ actuators fixed to the frame, who are subjected to an AC voltage and fixed frequency. This technique has all the advantages of the FBG s sensors (mass and small dimensions, electromagnetic immunity, high multiplexing s power and high sensitivity among others), in addition to allowing visualization of changes in the patterns of deformation caused by damage, by varying the frequency excitation. With respect to the interpretation of the results, the strategy employed was to separate the problem of detection and characterization of damage. Thus, the detection is performed by comparing the deformation energy of the surface of the specimens in the cases with and without defect, whereas the characterization is obtained through the use of artificial neural networks (ANN) by means of pattern recognition routines.

Dielectric elastomer actuators (DEAs) have been used for artificial muscles for years. Recently the DEA-based deformable surfaces have demonstrated controllable microscale roughness, ease of operation, fast response, and possibilities for programmable control. DEA muscles used in bioinspired robotic arms for large deformation and strong force also become desirable for their efficiency, low manufacturing cost, high force-to-weight ratio, and noiseless operation. The DEA-based responsive surfaces in microscale roughness control, however, exhibit limited durability due to irreversible dielectric breakdown. Lowering device voltage to avoid this issue is hindered by an inadequate understanding of the electrically-induced wrinkling deformation as a function of the deformable dielectric film thickness. Also, the programmable control and geometric analysis of the structured surface deformation have not yet been fully explored. Current methods to generate anisotropic wrinkles rely on mechanical pre-loading such as stretching or bending, which complicates the fabrication and operation of the devices. With a fixed mechanical pre-loading, the device can only switch between the flat state and the preset wrinkling state. In this thesis, we overcome these shortcomings by demonstrating a simple method for fabricating fault-tolerant electro-responsive surfaces and for controlling surface wrinkling patterns. The DEA-based system can produce different reversible surface topographies (craters, irregular wrinkles, structured wrinkles) upon the geometrical design of electrode and application of voltage. It remains functional due to its ability to self-insulate breakdown faults even after multiple high voltage breakdowns, and the induced breakdown punctures can be used for amplification of local electric fields for wrinkle formation at lower applied voltages. We enhance fundamental understanding of the system by using different analytical models combined with numerical simulation to discuss the mechanism and critical conditions for wrinkle formation, and compare it with the experimental results from surface topography, critical field to induce wrinkles in films of different thickness, and wrinkling patterns quantitatively analysed by different disorder metrics. Based on the results, we demonstrate its wide applicability in adjustable transparency films, dynamic light-grating filter, molding for static surface patterns, and multi-stable mirror-diffusor-diffraction grating device. For DEAs used for macroscopic-scale deformation in robotic arms, the main issue that undermines the performance of DEA muscles is the trade-off between strong force and large displacement, which limits the durability and range of potential robotic and automation applications of DEA-driven devices. In this thesis, this challenge is tackled by using DEAs in loudspeaker configuration for independent scaling-up of force and displacement, developing a theoretical prediction to optimise the operation of such DEAs in bioinspired antagonistic system to maximise speed and power of the robotic arm, and designing a clutch-gear-shaft mechanical system collaborating with the muscles to decouple the displacement and output force. Therefore, the trade-off between force and displacement in traditional DEA muscles can be resolved. The mechanical system can also convert the short linear spurt to an unlimited rotary motion. Combining these advantages, continuous movement with high output force can be accomplished.

Améliorer la sécurité routière passe par une meilleure compréhension des causes d'accidents. Il est donc nécessaire de développer des observatoires discrets pour étudier la manière de conduire de tous les automobilistes. Une partie de cette analyse implique l'utilisation de capteurs mesurant les trajectoires des véhicules sur une portion de route. Deux capteurs innovants ont été crées pour pallier au manque de capteurs suffisamment précis pour ces travaux de recherche : le premier est un capteur à fibres optiques présentant une succession de réseaux de Bragg et le second, protégé par un brevet, est fondé sur une technologie résistive. Le premier repère la déformation locale de fibres optiques noyées à moins d'un centimètre sous la surface de la chaussée. Il utilise la variation de longueurs d'onde engendré par l'extension de la fibre à la zone de contact roue - sol. En utilisant un algorithme adéquat, il est insensible à la température. Le second est constitué de deux conducteurs dont un est résistif. Le poids du véhicule engendre un contact électrique entre les deux conducteurs, transformant la résistance électrique de l'ensemble. Les modèles développés, électrique ainsi que de variation thermique, permettent sa meilleure utilisation. Ils ont été soumis à une expérimentation sur une route départementale. Le capteur optique s'avère plus performant mais coûteux. Le deuxième n'est pas assez robuste mais présente des perspectives intéressantes. / This action stake is not technology for itself. It is a great help the development of new safety functions, e.g. the estimation of driver’s behaviour based uponthe vehicle’s trajectory. This trajectory is determined via two sensors we developed. This system must not disturb the driver and should therefore remain invisible to him. The first one is a fiber Bragg grating (FBG) sensor. It detects local strain due to the vehicle weight. The fiber is embedded in the road thanks to resin used in other traffic sensors. The vehicle location is spotted according to the variations of Bragg wavelengths. The fiber extension located under the ground - wheel contact zone changes the step of the Bragg grating. The second one is based upon two conductors. One of them has a grater electrical resistance. The vehicle’s weight creates a link between the two conductors. The resulting electrical resistance provides a lateral position estimation of the vehicle. Electrical and thermic models and simulation even increase the sensor reliability. A caveat is lodged. Both of them were tested on a secondary road. To put in a nutshell, the FBG sensor gives better results but is very expensive (sensors and interrogator too). The resistance sensor is not much raw nevertheless it has interesting perspectives.

A slab-coupled optical fiber sensor (SCOS) falls into a narrow class of all-dielectric optical fiber electric field sensors, which makes it a perfect candidate for measurements of high electric fields in environments where presence of conductors is highly perturbing to the system under test. Its nonlinear response to high fields requires a new nonlinear calibration technique. A nonlinear calibration method is explained and demonstrated to successfully measure high electric fields, as well as high voltages with dynamic range up to 50 dB. Furthermore, a SCOS can be fitted into narrow spaces and make highly localized measurements due to its small size. This allows a SCOS to be integrated inside a standard high voltage coaxial cable, such as RG-218. Effects of partial discharge and arcing is minimized by development of a fabrication method to avoid introduction of impurities, especially air-bubbles, into the cable during SCOS insertion. Low perturbation of the measured voltage is shown by simulating the introduced voltage reflections to be on the order of –50 dB. It is also shown that a SCOS can be inserted into other cables without significant perturbation to the voltage. A complete high voltage and high electric field measurement system is built based on the high-voltage modifications of the SCOS technology. The coaxial SCOS is enhanced for robustness. Enhancements include packaging a SCOS into stronger ceramic trough, strengthening the fiber with kevlar reinforced furcation tubing and protecting the sensor with metal braces and protective shells. The interrogator is protected from electromagnetic interference with an RF-shielded box. Reduction in power losses introduced by the new PANDA-SCOS technology allows interrogator bandwidths to be increased up to 1.2 GHz. The whole measurement process is streamlined with dedicated software, developed specifically for high voltage and electric field measurements with support for the nonlinear calibration.

A slab-coupled optical fiber sensor (SCOS) falls into a narrow class of all-dielectric optical fiber electric field sensors, which makes it a perfect candidate for measurements of high electric fields in environments where presence of conductors is highly perturbing to the system under test. Its nonlinear response to high fields requires a new nonlinear calibration technique. A nonlinear calibration method is explained and demonstrated to successfully measure high electric fields, as well as high voltages with dynamic range up to 50 dB. Furthermore, a SCOS can be fitted into narrow spaces and make highly localized measurements due to its small size. This allows a SCOS to be integrated inside a standard high voltage coaxial cable, such as RG-218. Effects of partial discharge and arcing is minimized by development of a fabrication method to avoid introduction of impurities, especially air-bubbles, into the cable during SCOS insertion. Low perturbation of the measured voltage is shown by simulating the introduced voltage reflections to be on the order of −50 dB. It is also shown that a SCOS can be inserted into other cables without significant perturbation to the voltage.A complete high voltage and high electric field measurement system is built based on the high-voltage modifications of the SCOS technology. The coaxial SCOS is enhanced for robustness. Enhancements include packaging a SCOS into stronger ceramic trough, strengthening the fiber with kevlar reinforced furcation tubing and protecting the sensor with metal braces and protective shells. The interrogator is protected from electromagnetic interference with an RF-shielded box. Reduction in power losses introduced by the new PANDA-SCOS technology allows interrogator bandwidths to be increased up to 1.2 GHz. The whole measurement process is streamlined with dedicated software, developed specifically for high voltage and electric field measurements with support for the nonlinear calibration.

Ces travaux de thèse sont une contribution au projet de réalisation de matrices actives photoniques dans le cadre de la confection de lunettes à réalité augmentée. Un état de l’art des dispositifs actuels nous a permis de montrer l’encombrement engendré par l’utilisation d’un projecteur situé sur la monture. Pour s’en abstenir, l’utilisation du verre de lunette comme source d’image est limitée par la transparence des matrices actives classiques adressant un signal électrique avec des matériaux métalliques. L’utilisation de la photonique pour adresser chacun des pixels avec un signal optique guidée dans des matériaux diélectriques pourrait permettre d’en optimiser la transmission. Dans ce contexte, nos travaux concernent l’étude et la réalisation expérimentale de dispositifs incluant un guide d’onde et un système d’extraction activable. L'objectif est, d'une part, de sélectionner les matériaux et procédés technologiques adaptés pour former des lignes d'adressage photoniques et, d'autre part, d'associer les composants réalisés avec des éléments actifs permettant d’initier ou non l’extraction d’un guide d’onde. Le dispositif doit être transparent dans le visible afin de respecter les contraintes liées au secteur de l'optique ophtalmique. Dans un premier axe de recherche, des réseaux de diffraction micrométriques sont réalisés grâce au développement d’un procédé de photolithographie sur verre avant d’être imprégnés de cristaux liquides via la formation de cellules. La caractérisation, en transmission, des dispositifs formés permet d’étudier la capacité des molécules de cristal liquide à moduler l'intensité de diffraction pour passer d’un état diffractant à un état non diffractant. Une extinction de la diffraction de 90 à 99,9% selon l'épaisseur des structures est finalement mesurée avec l’application d’un champ électrique dans la cellule. La comparaison de ces résultats avec des calculs numériques permet de confirmer l’alignement des molécules à l’intérieur de la structure ainsi que leurs mobilités sous l’effet d’un champ électrique. Ce principe est, dans un second temps, étudié avec des composants photoniques et la réalisation de GMRF (Guided Mode Resonance Filter), association d'un guide d'onde et d'un réseau de diffraction. Des matériaux issus de la chimie sol-gel sont utilisés pour former des guides d'onde planaires et le développement d’un procédé de lithographie par nano-impression nous a permis d’obtenir les structures nanométriques requises. Divers bancs de caractérisation optique sont alors mis en place pour aboutir à plusieurs méthodes de couplage permettant d’obtenir une onde guidée dans le visible. Finalement, nous avons mesuré une modulation de 90% de l’intensité extraite par le GMRF via l’activation des cristaux liquides. / Ces travaux de thèse sont une contribution au projet de réalisation de matrices actives photoniques dans le cadre de la confection de lunettes à réalité augmentée. Un état de l’art des dispositifs actuels nous a permis de montrer l’encombrement engendré par l’utilisation d’un projecteur situé sur la monture. Pour s’en abstenir, l’utilisation du verre de lunette comme source d’image est limitée par la transparence des matrices actives classiques adressant un signal électrique avec des matériaux métalliques. L’utilisation de la photonique pour adresser chacun des pixels avec un signal optique guidée dans des matériaux diélectriques pourrait permettre d’en optimiser la transmission. Dans ce contexte, nos travaux concernent l’étude et la réalisation expérimentale de dispositifs incluant un guide d’onde et un système d’extraction activable. L'objectif est, d'une part, de sélectionner les matériaux et procédés technologiques adaptés pour former des lignes d'adressage photoniques et, d'autre part, d'associer les composants réalisés avec des éléments actifs permettant d’initier ou non l’extraction d’un guide d’onde. Le dispositif doit être transparent dans le visible afin de respecter les contraintes liées au secteur de l'optique ophtalmique. Dans un premier axe de recherche, des réseaux de diffraction micrométriques sont réalisés grâce au développement d’un procédé de photolithographie sur verre avant d’être imprégnés de cristaux liquides via la formation de cellules. La caractérisation, en transmission, des dispositifs formés permet d’étudier la capacité des molécules de cristal liquide à moduler l'intensité de diffraction pour passer d’un état diffractant à un état non diffractant. Une extinction de la diffraction de 90 à 99,9% selon l'épaisseur des structures est finalement mesurée avec l’application d’un champ électrique dans la cellule. La comparaison de ces résultats avec des calculs numériques permet de confirmer l’alignement des molécules à l’intérieur de la structure ainsi que leurs mobilités sous l’effet d’un champ électrique. Ce principe est, dans un second temps, étudié avec des composants photoniques et la réalisation de GMRF (Guided Mode Resonance Filter), association d'un guide d'onde et d'un réseau de diffraction. Des matériaux issus de la chimie sol-gel sont utilisés pour former des guides d'onde planaires et le développement d’un procédé de lithographie par nano-impression nous a permis d’obtenir les structures nanométriques requises. Divers bancs de caractérisation optique sont alors mis en place pour aboutir à plusieurs méthodes de couplage permettant d’obtenir une onde guidée dans le visible. Finalement, nous avons mesuré une modulation de 90% de l’intensité extraite par le GMRF via l’activation des cristaux liquides.

<p>The task of the project was to evaluate a differential phase shift keying demodulation technique by replacing a Mach-Zehnder interferometer receiver with an optical filter (Fiber Bragg Grating). Computer simulations were made with single optical transmission, multi channel systems and transmission with combined angle/intensity modulated optical signals. The simulations showed good results at both 10 and 40 Gbit/s. Laboratory experiments were made at 10 Gbit/s to verify the simulation results. It was found that the demodulation technique worked, but not with satisfactory experimental results. The work was performed at Eindhoven University of Technology, Holland, within the framework of the STOLAS project at the department of Electro-optical communication.</p>