The use of composite materials in industrial applications such as aeronautical, aerospace or wind energy production has greatly increased in recent decades. Due to their inherent properties, these materials allow lighter, larger and more resistant structures. However, the use of composite materials for components or structures with highly stringent requirements, is hampered by the lack of knowledge of their reliability. In this thesis, some fundamental aspects about the use of fibre Bragg grating (FBG) sensors for internal strain measurements in composite laminates are discussed. In addition, a highly accurate method for locating the crack tip position in mixed-mode delamination growth has been presented. Finally, an experimental application of FBGs to dynamic measurements in mode I fatigue test has been performed / L’ús de materials compostos en aplicacions de caràcter industrial com per exemple l’aeronàutica, aeroespacial o la de producció d’energia eòlica, ha crescut exponencialment durant les últimes dècades. Degut a les seves extraordinàries propietats, l’ús d’aquests materials permet la construcció d’estructures més lleugeres, grans i resistents, tot i que el seu ús en components d’alta responsabilitat estructural està limitat per la manca de coneixement en relació a la seva fiabilitat estructural. En aquesta tesi es discuteixen alguns aspectes significants sobre l’ús de FBGs per a mesurar camps de deformació en l’interior de laminats de material compòsit, s’ha analitzat també la capacitat de localització de la punta d’una esquerda en creixement de mode mixt i per últim s’ha desenvolupat una aplicació pràctica dels FBG en temps real en assaigs a fatiga en mode I

<p>The main objectives of this thesis were to develop a lowtemperature PECVD process suitable for optoelectronicintegration, and to optimize silica glass composition forUV-induced modifications of a refractive index in PECVDfabricated planar devices. The most important achievement isthe successful development of a low temperature silicadeposition, which for the first time makes it is possible tofabricate good quality low loss integrated components whilekeeping the temperature below 250oC during the entirefabrication process. Two strong absorption peaks thatappear at1.5 mm communication window due to N-H and Si-H bonds have beencompletely eliminated by process optimization. This openspossibilities for monolithic integration with other,temperature sensitive devices, such as semiconductor lasers anddetectors, or polymer-based structures on the common siliconplatform. PECVD technology for low loss amorphous silicon inapplication to SiO2/Si based photonic crystal structures hasbeen also optimized to remove hydrogen incorporated during thedeposition process, responsible for the porosity of thedeposited material and creation of similar to silica absorptionbands.</p><p>Change of the refractive index of germanium doped silicaunder UV irradiation is commonly used for fabrication of UVinduced fiber Bragg gratings. Here we describe our achievementsin fabrication of fiber Bragg gratings and their application todistributed sensor systems. Recently we have built up a laserlab for UV treatment in application to planar technology. Wehave demonstrated the high photosensitivity of PECVD depositedGe-doped glasses (not thermally annealed) even without hydrogenloading, leading to a record transmission suppression of 47dBin a Bragg grating photoinduced in a straight buried channelwaveguide. We have also used a UV induced refractive indexchange to introduce other device modifications or functions,such as phase shift, wavelength trimming and control ofpolarization birefringence.The developed low temperature technology and the UVprocessing form a unique technology platform for development ofnovel integrated functional devices for optical communicationsystems.</p><p>A substantial part of the thesis has been devoted tostudying different plasma deposition parameters and theirinfluence on the optical characteristics of fabricatedwaveguides to find the processing window giving the besttrade-off between the deposition rate,chamber temperatureduring the process, optical losses and presence of absorptionbands within the interesting wavelength range. The optimalconditions identified in this study are low pressure (300-400mTorr), high dilution of silane in nitrous oxide and high totalflow (2000 sccm), low frequency (380 KHz) RF source and high RFpower levels (800-1000 W).</p><p>The thesis provides better understanding of the plasmareactions during the deposition process. RF Power is the keyparameter for increasing the rate of surface processes so as toaccommodate each atomic layer in the lowest energy statepossible. All the process conditions which favor a moreenergetic ion bombardment (i.e. low pressure, low frequency andhigh power) improve the quality of the material, making it moredense and similar to thermal oxide, but after a certain pointthe positive trend with increasing power saturates. As theenergy of the incoming ion increases, a competing effect setsin at the surface: ion induced damage and resputtering.</p><p>Finally, the developed technologies were applied for thefabrication of some test and new concept devices for opticalcommunication systems including multimode interference (MMI)-based couplers/splitters, state-of-the-art arrayed waveguidegrating-based multi/ demultiplexers, the first Bragg gratingassisted MMI-based add-drop multiplexer, as well as moreresearch oriented devices such as a Mach-Zehnder switch basedon silica poling and a Photonic Crystal-based coupler.</p><p><b>Keywords:</b>silica-on-silicon technology, PECVD, plasmadeposition, photonic integrated circuits, planar waveguidedevices, UV Bragg gratings, photosensitivity, arrayed waveguidegratings, multimode interference couplers, add-dropmultiplexers.</p>

The subject of this thesis is the exploration of new concepts for compact solid-state lasers in the visible and near-infrared spectral range using new components such as volume Bragg gratings for wavelength stabilisation and wavelength tuning. Also single-walled carbon nanotubes for mode-locking and Q-switching of lasers have been studied.We have developed a new method for the tuning of solid-state lasers by replacing a dielectric mirror with a transversally chirped volume Bragg grating, which allows smooth wavelength tuning without additional elements inside the laser cavity. The result is a more compact laser, since the tuning mechanism and output coupler are incorporated in one component. Another benefit is an increased efficiency, since additional elements inside the cavity will always add to the total loss of the laser. This has been demonstrated for a broadband ytterbium laser around 1 µm and a single-longitudinal-mode Nd:YVO4 laser around 1.06 µm. A volume Bragg grating has also been used to construct an efficient, narrow-linewidth ytterbium fiber laser and the employment of a volume Bragg gratingas the pump mirror of a solid-state laser for frequency-doubling has been investigated. Both lasers represent a practical solution, eliminating the use of additional intracavity elements. Second-harmonic generation is an efficient way to access the visible spectral range using diode-pumped solid-state lasers. However, these lasers can suffer from large amplitude fluctuations, which has been analyzed in more detail for an optically-pumped semiconductor disk-laser and a volume Bragg grating locked ytterbiumlaser. The control of those amplitude fluctuations is very important, since many applications like fluorescence microscopy require a laser with a constant output power and as little noise as possible. In addition to this, we have demonstrated, that saturable absorbers based on quan-tum dots and carbon nanotubes can be used to mode-lock compact laser at a wavelength around 1.03 µm. Those lasers have many interesting applications incommunications, clock generation, metrology and life sciences. / <p>QC 20130507</p>

SWIFTS (pour Stationary-Wave Integrated Fourier-Transform Spectrometer) est un concept de spectromètre s'appuyant sur l'optique intégrée pour proposer un système de mesure compact et de très haute résolution. Il combine une technique d'interférométrie développée par Gabriel Lippmann avec des technologies de microélectroniques actuelles. La technologie SWIFTS sera ici utilisée en tant qu'interrogateur de fibre de Bragg. En effet, combiner ce spectromètre avec des fibres de Bragg très sensibles, telle qu'une cavité Fabry-Perot à réseaux de Bragg (GFPC) d'une longueur de 20 mm, permettra de mesurer des variations de température et de déformation très précises. Les applications des fibres de Bragg sont nombreuses, particulièrement dans la surveillance de structure de génie civil ou dans la sureté nucléaire avec des précisions de l'ordre du microstrain. Cependant, les capteurs par fibres de Bragg n'ont jamais atteint la sensibilité nécessaire aux observations en science de la terre. Une précision de quelques dizaines de nanostrain serait pourtant d'un intérêt majeur dans l'étude des processus volcaniques et sismologiques. Je présente dans cette thèse la première utilisation d'un tel spectromètre de Fourier associé à des capteurs de Bragg pour mesurer des déformations dans différentes gammes allant du millistrain au nanostrain. Dans un premier temps, des déformations sur une petite structure en béton armé amenée jusqu'à l'état limite de fissuration permettront de qualifier différents capteurs à fibres de Bragg dans leur milieu d'usage. Dans un deuxième temps, des mesures de déformations liées au phénomène de la marrée terrestre sont proposées. Ces mesures, effectuées au Laboratoire Souterrain à Bas Bruit (LSBB) de Rustrel, donnent des précisions de l'ordre de 30 nanostrains sur une courte base et ouvrent la voie à d'autres mesures de phénomènes géophysiques pour cet instrument. / SWIFTS, or Stationary-Wave Integrated Fourier-Transform Spectrometer, is an extremely integrated very high resolution spectrometer. This spectroscopy technology represents a major advance in the field and will be used here as a Fiber Bragg Gratings interrogator. Combining such a spectrometer with very sensitive Bragg sensors, like grating Fabry-Perot cavity (GFPC) as long as 20 mm, will allow to measure high precision temperature or strain variation. Applications of Bragg sensors are numerous, especially in structure monitoring and nuclear power plants safety. Despite promising capabilities, Bragg sensors never reached the desired sensibility for earth-science observation purposes. Present applications are restricted to civil-engineering strain-gauge sensors with microstrain sensitivity. However, the ability to detect and record signals of the order of a few tens of nanostrain is of great interest to monitor and model the volcanic and seismological processes. I demonstrate in this thesis the first use of a Fourier-Transform spectrometer combined with Fiber Bragg Sensors in a field configuration to achieve extremely high precision measurement on earth's crustal deformation. Precisions of thirty nanostrains on a very short base were achieved in the Low-Noise Underground Laboratory (LSBB) at Rustrel. Crustal monitoring opens the way for numerous applications especially in geophysics. A second study presented in this thesis aims at benchmarking several strain sensors based on optical fiber Bragg grating. For this purpose, two reinforced concrete beams have been tested in three points bending up to ultimate limit state.

Neste trabalho foi estudada a aplicação das redes de Bragg em fibra óptica, como sensores no monitoramento e mapeamento térmico de um painel fotovoltaico instalado em ambiente aberto. Também foi analisada a capacidade desses sensores em detectar anomalias elétricas do painel, as quais são manifestadas pelas mudanças na temperatura. Devido ao fato de ser pioneiro no estudo da fibra óptica em painéis fotovoltaicos, o presente trabalho buscou comparar os resultados alcançados por esta tecnologia com os dados das demais técnicas de medição de temperatura, como por exemplo, o PT100 e câmera IR. Os ensaios foram realizados utilizando um painel fotovoltaico instalado em ambiente aberto, onde as suas variações de temperatura foram medidas por 27 sensores de fibra óptica instalados em sua superfície frontal. Durante todos os ensaios as condições ambientais de temperatura ambiente, nível de radiação solar e velocidade do vento foram monitorados. Os resultados demonstraram potencialidade de utilização das redes de Bragg em fibra óptica na detecção de variações térmicas ocasionadas por fatores ambientais ou aquecimento nas células. / This paper has been studying the applications of Bragg gratings in optical fibers, as sensors for thermal mapping and monitoring on photovoltaic panel surface which was installing in an open environment. We also analyzed the ability of optical fibers sensors to detect electrical anomalies in the panel, which are manifested by the changes in its temperature. Because it was pioneering in study of optical fiber application into photovoltaic panel, this paper's objective is compare the results between this technology and the other techniques for temperature measurements, for example when are used the PT100 sensors or infrared camera. Assays were performed using a photovoltaic panel that is installed in an open environment, its temperature changes were measured by a total of 27 optical fiber sensors installed on the front surface. During the tests, the environmental conditions of temperature, level of solar radiation and wind speed, were monitored. The results demonstrate the potential use of Bragg gratings in optical fiber for detecting thermal fluctuations caused by environmental factors or by heating the cells.

Sensores óticos baseados em redes de Bragg em fibras óticas estão se tornando uma tecnologia madura e ganhando espaço nas indústrias das mais diversas áreas. Para tal, essa tecnologia deve estar adaptada para ser integrada facilmente ao meio industrial. Com base nisso esta pesquisa apresenta o desenvolvimento de uma ferramenta computacional para duas tecnologias de interrogação de sensores baseados em Redes de Bragg em fibras óticas (FBGs). Além de adquirir os dados dos interrogadores a ferramenta computacional tem por objetivo processar os dados, para isso foi necessário o desenvolvimento de um algoritmo de detecção de picos. Este trabalho também apresenta os resultados obtidos de comparações entre as ferramentas comerciais para cada tecnologia de interrogação e a ferramenta desenvolvida durante esta pesquisa. / Optical sensors based on Fiber Bragg Gratings technologies are becoming a mature technology and starting to com now in the industrial area. To make this possible this technology need to be adapted to be easily integrated in the existing industrial systems. Based on this considerations, this research presents the development of a computational tool for two Fiber Bragg Gratings interrogation technologies. In addition to acquiring data from the interrogator the computational tool is intended to process the data, and this makes necessary to develop a peak detection algorithm. This work also presents the results obtained by comparing the commercial software’s of each interrogation system to the computational toll developed during this research.

Neste trabalho foi estudada a aplicação das redes de Bragg em fibra óptica, como sensores no monitoramento e mapeamento térmico de um painel fotovoltaico instalado em ambiente aberto. Também foi analisada a capacidade desses sensores em detectar anomalias elétricas do painel, as quais são manifestadas pelas mudanças na temperatura. Devido ao fato de ser pioneiro no estudo da fibra óptica em painéis fotovoltaicos, o presente trabalho buscou comparar os resultados alcançados por esta tecnologia com os dados das demais técnicas de medição de temperatura, como por exemplo, o PT100 e câmera IR. Os ensaios foram realizados utilizando um painel fotovoltaico instalado em ambiente aberto, onde as suas variações de temperatura foram medidas por 27 sensores de fibra óptica instalados em sua superfície frontal. Durante todos os ensaios as condições ambientais de temperatura ambiente, nível de radiação solar e velocidade do vento foram monitorados. Os resultados demonstraram potencialidade de utilização das redes de Bragg em fibra óptica na detecção de variações térmicas ocasionadas por fatores ambientais ou aquecimento nas células. / This paper has been studying the applications of Bragg gratings in optical fibers, as sensors for thermal mapping and monitoring on photovoltaic panel surface which was installing in an open environment. We also analyzed the ability of optical fibers sensors to detect electrical anomalies in the panel, which are manifested by the changes in its temperature. Because it was pioneering in study of optical fiber application into photovoltaic panel, this paper's objective is compare the results between this technology and the other techniques for temperature measurements, for example when are used the PT100 sensors or infrared camera. Assays were performed using a photovoltaic panel that is installed in an open environment, its temperature changes were measured by a total of 27 optical fiber sensors installed on the front surface. During the tests, the environmental conditions of temperature, level of solar radiation and wind speed, were monitored. The results demonstrate the potential use of Bragg gratings in optical fiber for detecting thermal fluctuations caused by environmental factors or by heating the cells.

Sensores óticos baseados em redes de Bragg em fibras óticas estão se tornando uma tecnologia madura e ganhando espaço nas indústrias das mais diversas áreas. Para tal, essa tecnologia deve estar adaptada para ser integrada facilmente ao meio industrial. Com base nisso esta pesquisa apresenta o desenvolvimento de uma ferramenta computacional para duas tecnologias de interrogação de sensores baseados em Redes de Bragg em fibras óticas (FBGs). Além de adquirir os dados dos interrogadores a ferramenta computacional tem por objetivo processar os dados, para isso foi necessário o desenvolvimento de um algoritmo de detecção de picos. Este trabalho também apresenta os resultados obtidos de comparações entre as ferramentas comerciais para cada tecnologia de interrogação e a ferramenta desenvolvida durante esta pesquisa. / Optical sensors based on Fiber Bragg Gratings technologies are becoming a mature technology and starting to com now in the industrial area. To make this possible this technology need to be adapted to be easily integrated in the existing industrial systems. Based on this considerations, this research presents the development of a computational tool for two Fiber Bragg Gratings interrogation technologies. In addition to acquiring data from the interrogator the computational tool is intended to process the data, and this makes necessary to develop a peak detection algorithm. This work also presents the results obtained by comparing the commercial software’s of each interrogation system to the computational toll developed during this research.

Sensors have become essential elements in human life for safe and comfortable existence in the ever demanding world. Various technologies over decades have contributed in their own way fulfilling innumerable sensing requirements. The discovery of optical sensor technologies has revolutionized the sensing field due to their inherent advantages. Among the large number of fiber optic sensor technologies, FBG based sensors have become widely known and popular within and outside the photonics community and has seen a prominent rise in their utilization. This thesis explores the use of FBG sensors for a wide range of applications scanning across a variety of engineering and medical applications, in the areas of civil engineering, biomechanical engineering, aerospace engineering, geoengineering, etc. It also deals with newer methods of packaging FBG sensors for the measurement of specific engineering parameters like strain, temperature, pressure, displacement and vibration. In the field of civil engineering, FBG sensors are employed for strain sensing on a prism and furthermore tested on a full size brick wallet. During this study, emphasis is made on substituting traditional sensors by specially packaged FBG sensors with the intent of either enhancing the sensing system’s performance or in merging/uniting the inherent advantages of FBG sensors. In the area of biomechanics, a novel sensor methodology using FBG sensors, for measuring surface strains generated on the skin of the calf muscle during various leg exercises is proposed. This methodology is used to address one of the most critical and life threatening issues in long distance air travel, namely the Deep Vein Thrombosis. Further, a FBG sensor based plantar sensing plate, is designed and developed, to measure plantar strain distribution in foot and also to analyze the postural stability. In the field of aerospace engineering, FBG sensors are used for addressing two of the most vital issues; Structural Health Monitoring (SHM) and direct measurement of pressure and temperature on the surface of an aircraft under hypersonic wind flow. Carbon Fiber Composite coupon level testing is carried out to obtain a generic strain calibration factor for the FBG sensor. Further, FBG sensors are exploited for the direct measurement of absolute temperature and pressure on the leeward surface of blunt cone at hypersonic wind speeds. In the domain of geoengineering, the feasibility studies have been undertaken to use a FBG as a seismic sensor and as a bore-well characterizing sensor. A novel FBG seismic sensor package is developed using a single FBG sensor to pick up the seismic waves propagating through the ground generated from earthquakes and ground tremors. Further, FBG sensors are used for measurement of temperature profiles in a bore-well to delineate and characterize the behavior of fractures during seasonal climatic changes. To summarize, the present thesis demonstrates a comprehensive experimental study which bring out the utility of FBG sensors in a variety of challenging applications.

[pt] Linhas de transmissão de energia são estruturas importantes em um sistema de energia elétrica. Devido à elevada energia transportada por essas redes, falhas em linhas de transmissão podem ter reflexos severos no fornecimento aos consumidores, não raro levando a apagões em áreas geograficamente extensas. Entre as possíveis origens de falhas está o rompimento dos cabos elétricos pela fadiga provocada pela vibração eólica. As grandes extensões territoriais percorridas pelas linhas de transmissão e a variedade de climas, relevos, vegetação e condições meteorológicas aos quais estão submetidas dificultam qualquer trabalho de previsão da ação do vento. A medição da vibração permite detectar de antemão a aproximação da falha, porém os instrumentos convencionais dependem de transdutores elétricos os quais, além de exigirem uma fonte de energia (normalmente não disponível junto a linhas de transmissão) para seu funcionamento, sofrem influência dos intensos campos elétricos e magnéticos existentes em torno dos cabos de energia. A imunidade das fibras ópticas a campos elétricos e magnéticos e a possibilidade de uso de sinal de entrada de baixa potência oferecem uma alternativa para a criação de instrumentos de medição usando a técnica das redes de Bragg. A presente dissertação contribui com o desenvolvimento de um acelerômetro biaxial a redes de Bragg para medição de vibração em cabos de linhas de transmissão de energia. Além dos aspectos teóricos e práticos envolvidos, são discutidos os resultados de ensaios de calibração de elevada exatidão e outros ensaios especiais que fundamentaram a avaliação metrológica e o estabelecemento da eficácia do referido instrumento. / [en] Overhead transmission lines play an important role on electric systems. Due to the high energy carried through those networks, failures on overhead lines can bring severe constraints on consumers supply, occasionally taking the form of blackouts in large geographic regions. Among the reasons of such failures is the breaking of electric cables caused by the fatigue originated from cyclic bending due to aeolian vibration. The large areas covered by overhead lines and the variety of climate, relief, vegetation and meteorological conditions under which they have to operate make it difficult to foresee the impact of wind Vibration measurements would allow anticipating the failure but conventional instruments depend upon electric transducers which, besides demanding a local source of energy (usually unavailable near overhead lines), suffer the influence of the high electric and magnetic fields around the energized cables. Optical fibers immunity against environments subjected to electrical and magnetic fields and the possibility of using low energy input signals offer the alternative of creating measuring instruments using Bragg gratings technique. This Master dissertation contributes with the development of a fiber Bragg grating biaxial accelerometer for measuring the vibration of overhead transmission line cables. Besides the theoretical and practical aspects related to the subject, the results of high precision calibration tests are discussed, together with other special tests which set the basis of the metrological evaluation and the establishment of the efficacy of the instrument.