<p>The fiber-to-the-x (FTTX) has been widely investigated as a leading access technology to meet the ever growing demand for bandwidth in the last mile. The passive optical network (PON) provides a cost-effective and durable solution. In this thesis, we investigate different aspects of the PON, in the search for cost-effective and high-performance designs of link system and devices.</p> <p>In Chapter 2, we propose a novel upstream link scheme for optical orthogonal frequency division multiplexing (OOFDM)-PON. The colorless laser diodes are used at the optical network units (ONUs), and the overlapped channel spectrum of orthogonal subcarrier multiplexing provides high spectral efficiency. At the optical line terminal (OLT), optical switch and all optical fast Fourier transform (OFFT) are adopted for high speed demultiplexing. The deterioration caused by the laser perturbation is also investigated.</p> <p>In Chapter 3, we design a novel polarization beam splitter (PBS), which is one of the most important components in polarization-controlled optical systems, e.g. the next-generation PON utilizing polarization multiplexing. Our PBS is built on a slab waveguide platform where the light is vertically confined. Planar lenses are formed to collimate and refocus light beam by converting the phase front of the beam. A planar subwavelength grating of a wedge shape induces the form birefringence, where the transverse electric (TE) and transverse magnetic (TM) waves have different effective refractive indices, and are steered to distinct directions. This design provides low insertion loss (< 0.9 dB) and low crosstalk (< -30 dB) for a bandwidth of 100 nm in a compact size, and can be realized by different material systems for easy fabrication and/or monolithic integration with other optical components.</p> <p>In Chapter 4, we study the mode partition noise (MPN) characteristics of the Fabry-Perot (FP) laser diode using the time-domain simulation of noise-driven multi-mode laser rate equation. FP laser is cheaper than the widely used distributed feedback (DFB) laser diode in PON, but its MPN is the major limiting factor in an optical transmission system. We calculate the probability density functions for each longitudinal mode. We also investigate the k-factor, which is a simple yet important measure of MPN. The sources of the k-factor are studied with simulation, including the intrinsic source of the laser Langevin noise, and the extrinsic source of the bit pattern.</p> / Doctor of Philosophy (PhD)

Les isolateurs optiques sont des composants non-réciproques très important dans les systèmes de télécommunication optique. Actuellement les composants commercialisés sont tous discrets, à cause de la difficulté d’intégration des matériaux magnéto-optiques avec les technologies de l’optique intégrée. L’objectif de ma thèse était d’ouvrir une nouvelle voie technologique pour aboutir à une telle intégration. Pour cela nous avons développé une approche basée sur l’utilisation d’un matériau magnéto-optique composite complètement compatible avec la technologie d’échange d’ions sur verre. Ce matériau est élaboré par la voie sol-gel organique-inorganique et dopé par des nanoparticules magnétiques de ferrite de Cobalt (CoFe204). Il a montré des potentialités très prometteuses, illustré par une rotation Faraday spécifique de 420°/cm (@1550nm). Ce composite est déposé par la méthode dip-coating sur un guide fait par échange ionique d’Ar+/Na+, avec des extrémités enterrées par la méthode d’enterrage sélective pour faciliter le couplage-découplage de la lumière dans la structure hybride. Enfin, un traitement thermique (<100°C) et un traitement UV compatibles avec le procédé d’échange d’ions sur verre sont appliqués sur le dispositif pour finaliser la couche magnéto-optique. La caractérisation optique de notre dispositif a montré une bonne distribution de la lumière entre la couche magnéto-optique et le guide fait par échange d’ions (un bon confinement latéral). De plus, l’application d’un champ magnétique longitudinal au composant a permis de démontrer une valeur de conversion de mode TE-TM qui correspond bien à la quantité de la lumière confinée dans la couche magnéto-optique et la biréfringence modale de la structure. Donc, le but principal de la thèse est atteint, et ces résultats montrent la faisabilité d’un convertisseur de mode TE-TM compatible avec la technologie d’optique intégrée sur verre / Optical isolators are essential nonreciprocal devices used in optical communication systems. Currently, these components are commercially available but only in bulk form, due to the difficulties to embed magneto-optical materials with integrated classical technologies. To overcome this problem, our group has developed a new approach based on composite magneto-optical matrix that is fully compatible with ion-exchanged glass waveguide technology. This material is developed by organic inorganic sol-gel process and doped by magnetic nanoparticles (CoFe2O4). Such a magneto-optical composite matrix has shown promising potentialities illustrated by a specific Faraday rotation of 420°/cm (@1550nm). Using dip-coating technique, a composite layer was coated on a glass substrate containing straight channel waveguide made by a silver/sodium ion exchange. The extremities of the guides were previously buried using selective buried method in order to facilitate coupling-decoupling of light in hybrid structure. Last, a soft annealing (<100°C) and UV treatment, both compatible with the ion-exchanged process, have been implemented to finalize the magneto-optical film. Optical characterization demonstrated a good distribution of light between the magneto-optical thin film and the ion-exchanged waveguide (good lateral confinement). Furthermore TE to TM mode conversion has been observed when a longitudinal magnetic field is applied to the device. The amount of this conversion is in good agreement with the distribution of light between the layer and the guide obtained by numerical calculations, and the modal birefringence of the structure. So, the aim of my thesis is achieved and the results demonstrate the feasibility of TE to TM mode converter fully compatible with glass integrated optics

We have developed a new modulation calorimetry technique using RF-Field heating. This technique eliminates temperature gradients across the sample leading to a higher precision in evaluating the heat capacity compared to the previous techniques. A frequency scan was carried out on a 8CB+aerosil sample showing a wide plateau indicating the region of frequency independent heat capacity. A temperature scan was then performed through the first-order nematic to isotropic and second order smectic-A to nematic transitions and was shown to be consistent with the previous work. The amplitude of the RF heating power applied to the sample depends on the permittivity and the loss factor of the sample. Since the permittivity of a dielectric material has a strong temperature dependence in liquid crystals, new information is obtained. The heat capacity measurements have a relative resolution of better than 0.06%, and the phase shift a resolution of 0.03%, were shown to be significant improvements over traditional heating methods. We then applied this new RF calorimetry on bulk and aerosil 8CB dispersions. For the bulk 8CB, the step-like character of smectic-A to nematic transition, and first order nematic to isotropic transitions indicated the strong dominance of the permittivity and the loss factor of the material. For the 8CB+aerosil samples at different silica density, our data were consistent with the previous work and provides clear evidence for the coupling between the smectic-A and nematic phases. We have undertaken a combined T-dependent optical and calorimetric investigation of CCN47+aerosil samples through the I-N transition over a range of silica densities displaying the double I-N transition peak. This work offers compelling evidence that the I-N transition with weak quenched random disorder proceeds via a two-step process in which random-dilution is followed by random-field interactions on cooling from the isotropic phase, a previously unrecognized phenomena.

Microstructured optical fibres (MOFs), also commonly called photonic crystal fibres or holey fibres, describe a type of optical fibre in which continuous channels of (typically) air run their entire length. These `holes' serve to both confine electromagnetic waves within the core of the fibre and to tailor its transmission properties. In order to understand and quantify both of these functions, a new computational algorithm was developed and implemented. It solves for the eigenvalues of Maxwell's wave equations in the two-dimensional waveguide cross-section, with radiating boundary conditions imposed outside the microstructure. This yields the leaky modes supported by the fibre. The boundary conditions are achieved exactly using a novel refinement scheme called the Adjustable Boundary Condition (ABC) method. Two implementations are programmed and their computational efficiencies are compared. Both use an azimuthal Fourier decomposition, but radially, a finite difference scheme is shown to be more efficient than a basis function expansion. The properties of the ABC method are then predicted theoretically using an original approach. It shows that the method is highly efficient, robust, automated and generally applicable to any implementation or to other radiating problems. A theoretical framework for the properties of modes in MOFs is also presented. It includes the use of the Bloch-Floquet theorem to provide a simpler and more efficient way to exploit microstructure symmetry. A new, but brief study of the modal birefringence properties in straight and spun fibres is also included. The theoretical and numerical tools are then applied to the study of polymer MOFs. Three types of fibres are numerically studied, fabricated and characterised. Each is of contemporary interest. Firstly, fabrication of the first MOFs with uniformly oriented elliptical holes is presented. A high degree of hole ellipticity is achieved using a simple technique relying on hole deformation during fibre draw. Both form and stress-optic birefringence are characterized over a broad scaled-wavelength range, which shows excellent agreement with numerical modelling. Secondly, an analysis of leaky modes in real air core MOFs, fabricated specifically for photonic band gap guidance, is then used to identify alternative guiding mechanisms. The supported leaky modes exhibit properties closely matching a simple hollow waveguide, weakly influenced by the surrounding microstructure. The analysis gives a quantitative determination of the wavelength dependent confinement loss of these modes and illustrates a mechanism not photonic band gap in origin by which colouration can be observed in such fibres. Finally, highly multimode MOFs (also called `air-clad' fibres) that have much wider light acceptance angles than conventional fibres are studied. An original and accurate method is presented for determining the numerical aperture of such fibres using leaky modes. The dependence on length, wavelength and various microstructure dimensions are evaluated for the first time for a class of fibres. These results show excellent agreement with published measurements on similar fibres and verify that bridge thicknesses much smaller than the wavelength are required for exceptionally high numerical apertures. The influence of multiple layers of holes on the numerical aperture and capture efficiency are then presented. It shows that a substantial increase in both these parameters can be achieved for some bridge thicknesses. Simple heuristic expressions for these quantities are given, which are based on the physical insight provided by the full numerical models. The work is then supported by the first fabrication attempts of large-core polymer MOFs with thin supporting bridges. These fibres exhibit relatively high numerical apertures and show good agreement with theoretical expectations over a very wide scaled-wavelength range.

Microstructured optical fibres (MOFs), also commonly called photonic crystal fibres or holey fibres, describe a type of optical fibre in which continuous channels of (typically) air run their entire length. These `holes' serve to both confine electromagnetic waves within the core of the fibre and to tailor its transmission properties. In order to understand and quantify both of these functions, a new computational algorithm was developed and implemented. It solves for the eigenvalues of Maxwell's wave equations in the two-dimensional waveguide cross-section, with radiating boundary conditions imposed outside the microstructure. This yields the leaky modes supported by the fibre. The boundary conditions are achieved exactly using a novel refinement scheme called the Adjustable Boundary Condition (ABC) method. Two implementations are programmed and their computational efficiencies are compared. Both use an azimuthal Fourier decomposition, but radially, a finite difference scheme is shown to be more efficient than a basis function expansion. The properties of the ABC method are then predicted theoretically using an original approach. It shows that the method is highly efficient, robust, automated and generally applicable to any implementation or to other radiating problems. A theoretical framework for the properties of modes in MOFs is also presented. It includes the use of the Bloch-Floquet theorem to provide a simpler and more efficient way to exploit microstructure symmetry. A new, but brief study of the modal birefringence properties in straight and spun fibres is also included. The theoretical and numerical tools are then applied to the study of polymer MOFs. Three types of fibres are numerically studied, fabricated and characterised. Each is of contemporary interest. Firstly, fabrication of the first MOFs with uniformly oriented elliptical holes is presented. A high degree of hole ellipticity is achieved using a simple technique relying on hole deformation during fibre draw. Both form and stress-optic birefringence are characterized over a broad scaled-wavelength range, which shows excellent agreement with numerical modelling. Secondly, an analysis of leaky modes in real air core MOFs, fabricated specifically for photonic band gap guidance, is then used to identify alternative guiding mechanisms. The supported leaky modes exhibit properties closely matching a simple hollow waveguide, weakly influenced by the surrounding microstructure. The analysis gives a quantitative determination of the wavelength dependent confinement loss of these modes and illustrates a mechanism not photonic band gap in origin by which colouration can be observed in such fibres. Finally, highly multimode MOFs (also called `air-clad' fibres) that have much wider light acceptance angles than conventional fibres are studied. An original and accurate method is presented for determining the numerical aperture of such fibres using leaky modes. The dependence on length, wavelength and various microstructure dimensions are evaluated for the first time for a class of fibres. These results show excellent agreement with published measurements on similar fibres and verify that bridge thicknesses much smaller than the wavelength are required for exceptionally high numerical apertures. The influence of multiple layers of holes on the numerical aperture and capture efficiency are then presented. It shows that a substantial increase in both these parameters can be achieved for some bridge thicknesses. Simple heuristic expressions for these quantities are given, which are based on the physical insight provided by the full numerical models. The work is then supported by the first fabrication attempts of large-core polymer MOFs with thin supporting bridges. These fibres exhibit relatively high numerical apertures and show good agreement with theoretical expectations over a very wide scaled-wavelength range.

Made available in DSpace on 2016-06-02T20:16:51Z (GMT). No. of bitstreams: 1 5339.pdf: 3033412 bytes, checksum: 3e684081236853aacfacccef70bd4635 (MD5) Previous issue date: 2009-10-02 / Financiadora de Estudos e Projetos / Lead titanate zirconate modified with lanthanum, or PLZT, is one the most ferroelectric compounds utilized in electronic devices, due to its versatility and low production costs in comparison with single-crystalline materials. When adequately prepared, this system presents good optical (high optical transmission) properties, in the visible and near infrared range, and can be electro-optically characterized. Recently, in the end of 90 s, it was verified its high potential as host of photoluminescent ions, as the lanthanide (rare-earth) family. The possibility to use its electro-optic properties (due to its ferroelectric characteristics) and its photoluminescent properties (achieved by the doping process) together ,enlarges the range of application of this system. In this way, the electro-optical characterization of doped PLZT ceramics becomes essential, besides the photonic characterization. In this work, the Senarmont compensator method for electro-optical characterization, or dynamic method, was instrumented, and the values of the induced (due to the quadratic electrooptic effect, Kerr) and permanent (due to the linear electro-optic effect, Pockels) birefringence were determined as a function of the temperature, wave-length and electric-field frequency, of the rare-earth (Nd2O3, Ho2O3, Er2O3, Tm2O3 e Yb2O3) doped PLZT, with La/Zr/Ti=9/65/35, ceramics. The results shown a relationship between of the electro-optic (electro-optic coefficients, or birefringence values) and the dielectric, ferroelectric and structural properties (studied in others works) of the ceramics, that were related with the site occupancy and the structural defects due to the aliovalent dopant. It also can be identified two distinct birefringence dependence as a function of the electric field, for the same electro-optic effect (Kerr, or Pockels), identified as a function of the doping process. In the case of electro-optical characterizations in function of the variable frequency, was observed an agreement with the characterization ferroelectric results made in other works in GCFerr, being evidenced the reduction of electro-optical properties with increasing frequency, where if it observed the occurrence of anomalies in the Pockels response with direct influence on the response Kerr. The characterization as a function of wavelength showed the occurrence of two types of behavior depending on the dopant ion used, being one of them the reduction of the values of birefringence with increasing wavelength (the samples pure and doped ions neodymium (Nd) and ytterbium (Yb)), with a tendency to expected behavior in the literature, however, in the second was seen irregular increase birefringence with increase wavelength (for samples doped with ions holmio ( Ho), erbium (Er) and thulium (Tm),not existing relation with to the theoretical models adopted. In relation the characterization as a function of temperature, this was carried through in a temperature interval that understood the characteristic temperatures of systems relaxores (freezing temperature (TF), the maximum dielectric permittivity (TM (e)) and Burns (TB)), except for the sample doped with neodymium ions, whose freezing temperature is below interval worked. By the curve of birefringence (&#916;&#61472;n) as a function of temperature was possible to determine the temperature of maximum birefringence for each of the samples, correlated them with each other. Through the curve (d &#916;&#61472;n / dt) vs. T was possible to identify a relationship between the maximum variations, positive and negative birefringence with the temperature characteristics TF and TB. / Entre os sistemas ferroelétricos, o sistema titanato zirconato de chumbo modificado com lantânio (PLZT) é um dos mais amplamente utilizados em dispositivos eletrônicos, dada sua versatilidade em aplicações e relação de custo quando comparado aos materiais monocristalinos utilizados nessa mesma área. Quando preparado pelo devido método de síntese, apresenta excelentes propriedades óticas (altos valores de transmissão ótica) desde a região do visível ao infravermelho próximo, possibilitando uma adequada caracterização de suas propriedades óticas e eletro-óticas. Recentemente, a partir do final da década de 90, foi verificada sua alta potencialidade como matriz hospedeira para íons fotoluminescentes, como os da família dos lantanídeos (ou terras-raras). A possibilidade do uso conjunto das propriedades eletro-óticas (dado seu caráter ferroelétrico) e de suas propriedades luminescentes (devido à incorporação de dopantes laser-ativos) aumentou ainda mais a possibilidade de aplicação desses materiais. Desse modo, a caracterização eletro-ótica das cerâmicas de PLZT dopado torna-se indispensável, além de sua caracterização fotônica. Sendo assim, neste trabalho foi instrumentado um sistema de caracterização eletro-ótica, utilizando o método do compensador Senarmont, também conhecido como método dinâmico, para determinar os valores da birrefringência induzida (devido ao efeito eletro-ótico quadrático, Kerr) e a permanente (devido ao efeito eletro-ótico linear, Pockels) em função da temperatura, comprimento de onda e frequência do campo elétrico de prova para composições cerâmicas de PLZT na razão La/Zr/Ti=9/65/35, dopadas com os óxidos terras-raras Nd2O3, Ho2O3, Er2O3, Tm2O3 e Yb2O3, na quantidade de 1,0% em peso. Os resultados mostraram que há uma relação entre as propriedades eletro-óticas encontradas (seja na forma de valores dos coeficientes eletro-óticos, ou na variação da birrefringência) com as propriedades dielétricas, ferroelétricas e estruturais (já observadas em outros trabalhos do grupo de pesquisa no qual esta dissertação foi realizada) das cerâmicas que, por sua vez, foram relacionadas com o tipo de ocupação e de defeitos gerados devido à incorporação dos dopantes. Além disso, foi possível observar que para uma mesma composição pode ocorrer a presença dos dois tipos de efeitos eletro-óticos - Kerr e Pockels - com proporções distintas em função do tipo de dopante. Através desse método, para esse conjunto de amostras, também foi possível identificar dois tipos distintos de variações da birrefringência em função do campo elétrico para um mesmo efeito eletro-ótico (Kerr, ou Pockels), que também puderam ser associados com o tipo de ocupação dos dopantes. Em se tratando das caracterizações eletro-óticas em função da variável frequência, foi observada uma concordância com os resultados da caracterização ferroelétrica, realizada em outros trabalhos no GCFErr, sendo evidenciada a redução das propriedades eletro-óticas com o aumento da frequência, em que se observou a ocorrência de anomalias na resposta Pockels com influência direta na resposta Kerr. A caracterização como uma função do comprimento de onda mostrou a ocorrência de dois tipos de comportamentos, dependendo do íon dopante utilizado, sendo um deles a redução dos valores da birrefringência com o aumento do comprimento de onda (caso das amostras pura e dopadas com os íons neodímio (Nd) e itérbio (Yb)), havendo certa tendência ao comportamento previsto em literatura, no entanto, no segundo caso foi constatado o aumento irregular da birrefringência com o aumento do comprimento de onda (caso das amostras dopadas com os íons holmio (Ho), érbio (Er) e túlio (Tm), não havendo relação com os modelos teóricos adotados. Quanto à caracterização em função da temperatura, esta foi realizada em um range de que compreendeu as temperaturas características de sistemas relaxores (de freezing (TF(e)), máxima permissividade dielétrica (TM(e)) e Burns (TB(e))), exceto para a amostra dopada com o íon neodímio, cuja TF(e) estava abaixo do intervalo considerado. Através da curva de birrefringência (&#916;n) em função da temperatura foi possível determinar a temperatura de máxima birrefringência para cada uma das amostras, correlacionado-as entre si. Através da curva de (d&#916;n/dt) vs. T, foi possível constatar uma relação entre as máximas variações, positiva e negativa, da birrefringência com as temperaturas características TF e TB.

Les céramiques transparentes élaborées par cristallisation complète du verre constituent une nouvelle famille de matériaux de qualité photonique en compétition avec la technologie des monocristaux pour les applications optiques. Cette approche verrière offre des avantages considérables par rapport aux monocristaux et aux céramiques polycristallines frittées : un coût réduit, la possibilité d’une production à grande échelle, une large gamme de compositions chimiques accessibles, une mise en forme plus souple et un taux de dopage élevé. Dans le cadre de ce travail, nous avons synthétisé des céramiques polycristallines transparentes de Sr3Al2O6 et Sr3Ga2O6 (structures cubiques) par cristallisation complète du verre de même composition. Les verres d'aluminate de strontium (75SrO-25Al2O3) et de gallate de strontium (75SrO-25Ga2O3) sont élaborés par lévitation aérodynamique couplée à un dispositif de chauffage laser. La transparence de la céramique de Sr3Al2O6 obtenue s’explique par son isotropie optique, ses joints de grains très fins et sa structure totalement dense (non poreuse). Nous avons également développé une nouvelle famille de céramiques transparentes Sr1+x/2Al2+xSi2-xO8 (0<x≤0.4) obtenues par cristallisation complète et congruente du verre. La transmission exceptionnelle de plus de 90% dans la gamme visible et proche infrarouge est expliquée grâce à des études microstructurales et structurales. Cette transparence qui atteint la limite théorique est associée à une biréfringence quasi nulle, des joints de grains très fins et une porosité nulle. Les études par RMN prouvent l'existence d'un désordre chimique qui est à l'origine de la valeur pratiquement nulle de la biréfringence calculée par DFT. Ces matériaux céramiques polycristallins évolutifs et hautement transparents sont des candidats prometteurs pour une large gamme d'applications optiques et photoniques dans les gammes IR et visible. Cette étude a donc conduit à de nouvelles céramiques transparentes, avec des valeurs de transmission jamais atteintes jusqu’à présent pour des oxydes. Elle propose également une nouvelle approche pour l'obtention de céramiques transparentes dans le cas de matériaux anisotropes : introduire un désordre chimique contrôlé au sein du matériau afin d’induire une isotropie optique. Ce concept ouvre la voie à de nouvelles compositions, étendant ainsi le domaine des céramiques transparentes et de leurs applications. / Transparent polycrystalline ceramics elaborated by full crystallization from glass are an emerging class of photonicquality materials competing with single crystal technology, especially for optical applications. This approach provides considerable advantages over single crystals and polycrystalline sintered ceramics represented by cost effectiveness, large scale production, wide range of accessible chemical compositions, easy shaping and high doping level hosting structure. In this work, we show the preparation of transparent cubic Sr3Al2O6 and Sr3Ga2O6 polycrystalline ceramics by full crystallization from the parent strontium aluminate (75SrO-25Al2O3) and strontium gallate (75SrO-25Ga2O3) glasses elaborated by aerodynamic levitation coupled to laser heating system. The transparency of the obtained Sr3Al2O6 ceramics is explained by their optical isotropy, thin grain boundaries and highly dense (non-porous) microstructure. We also show a series of novel Sr1+x/2Al2+xSi2-xO8 (0<x≤0.4) oxide compositions leading to highly transparent and readily scalable polycrystalline ceramics to be obtained by full congruent glass crystallization. The outstanding transparency exceeding 90% in the visible and near IR range is explained through different microstructural and structural (average and local) studies. This transparency, reaching the theoretical limit, is associated to the almost null birefringence, thin grain boundaries and non-porosity. NMR experiments prove the existence of chemical disorder which is at the origin of the relatively zero birefringence value calculated by DFT computations. These scalable and highly transparent polycrystalline ceramic materials are promising candidates for a wide range of optical and photonic applications in the IR and visible ranges. This study besides revealing new ceramic compositions with previously unreported transmission values for micro-scale polycrystalline materials, proposes a new approach for obtaining transparent ceramics in anisotropic materials. This approach consists in inducing a controlled chemical disorder within the material in order to induce optical isotropy. It is anticipated that this proposed concept will open the way to different composition candidates to be elaborated as transparent polycrystalline ceramics, thus extending the ceramic technology domain and its applications.

Made available in DSpace on 2016-03-15T19:37:31Z (GMT). No. of bitstreams: 1 Rodrigo Cesar Ribeiro Miraglia.pdf: 2147088 bytes, checksum: 67087392fe4b03bb24d9a164fd92ceed (MD5) Previous issue date: 2010-08-20 / Fundo Mackenzie de Pesquisa / Sensors based on optical fibers are being increasingly used in hostile environments for measuring pressure, temperature, stress, chemical and biological parameters, etc. These sensors have the advantage of having reduced size and weight, immunity to electromagnetic interference, of being chemically inert, and also allowing the distributed measurement of the respective parameter along the fiber. Microstructured optical fibers have characteristics that are relevant to sensing applications, such as freedom of design of their internal structure obtained by varying the diameter of the holes and the distances between them, among other parameters, which is not applicable in conventional optical fibers. The present work aims to use a microstructured optical fiber as a distributed sensor for hydrostatic pressure, using the POTDR (Polarization Optical Time-Domain Reflectometry) and the OFDR (Optical Frequency-Domain Reflectometry) measurement techniques. The application of hydrostatic pressure on the fiber changes its birefringence and, consequently, the evolution of the states of polarization, which is the parameter monitored by the techniques. By monitoring the changes of these states, it is possible to infer the changes in applied pressure. The study is undertaken via simulations and analysis, both performed in the software MatLab. / Sensores baseados em fibras ópticas vêm sendo cada vez mais utilizados em ambientes hostis para medição de pressão, temperatura, stress, análise química e biológica, etc. Esses sensores têm a vantagem de possuírem tamanho e peso reduzidos, imunidade à interferência eletromagnética, de serem quimicamente inertes, e também permitirem a medição distribuída do parâmetro a ser analisado ao longo da fibra. As fibras ópticas microestruturadas possuem características relevantes na aplicação de sensoriamento, tal como a liberdade de construção de sua estrutura interna variando o diâmetro dos buracos e a distância entre eles, entre outros parâmetros, que não são aplicáveis em fibras ópticas convencionais. Este trabalho tem como objetivo estudar uma fibra óptica microestruturada como sensor distribuído de pressão hidrostática, utilizando as técnicas de medição POTDR (Polarization Optical Time-Domain Reflectometry) e OFDR (Optical Frequency-Domain Reflectometry). A aplicação de pressão hidrostática sobre a fibra altera sua birrefringência e, consequentemente, a evolução do seu estado de polarização, sendo este último o parâmetro monitorado pelas técnicas. Analisando-se a mudança deste estado, pode-se inferir a mudança de pressão aplicada. O estudo é realizado através de simulações e análises efetuadas no software MatLab.

Cette thèse traite du contrôle et de la caractérisation de l'alignement et de l'orientation du point de vue théorique et expérimental. L'alignement d'une molécule linéaire consiste à obtenir une probabilité élevée de localisation de l'axe internucléaire symétrique autour de l'axe de polarisation du champ tandis que l'orientation privilégie un sens particulier le long du champ. L'orientation à l'aide d'impulsions bi couleur (2+1) non résonnantes est étudiée en détail et les conditions permettant d'obtenir une orientation efficace sont examinées. Un schéma bi couleur où la deuxième harmonique est en quasi-résonance avec un niveau vibrationnel de la molécule est également étudié. Cette technique présente l'avantage d'offrir un paramètre supplémentaire à savoir l'écart à la résonance qui peut être ajusté de manière à optimiser l'orientation moléculaire. Finalement une nouvelle technique expérimentale de détection de l'alignement moléculaire est présentée. Celle-ci permet une détection monocoup de l'alignement moléculaire sur une étendue temporelle jusqu'alors inégalée. / This thesis is about the control and characterisation of the alignment and orientation of molecules by ultra short laser pulses on a theoretical and experimental approach. Alignment corresponds to a symmetric angular distribution of the molecular axis peaked along the laser field axis, whereas orientation provides an asymmetric distribution favouring one spatial direction. Orientation by sudden two-colour (2+1) pulses is studied extensively for the non resonant case and conditions required for achieving significant orientation are explored. A second two-colour scheme, where the second harmonic is in quasi resonance with a vibrational level of the molecule, is also presented and discussed. The last technique has the advantage to offer the detuning of the laser frequency as an additional free parameter, which can be adjusted to enhance molecular orientation. A new experimental polarization imaging 2D technique for the detection alignment is also developed. Experimental results on single shot detection of molecular alignment achieved over an unprecedented temporal span are presented.

<p></p><p>This doctoral dissertation takes the reader through a journey where applied shear rheology and flow-velocimetry are used to understand the mesoscopic factors that control the flow behavior of three microstructured fluids. Three individual protocols that measure relative physical and mechanical properties of the flow are developed. Each protocol aims to advance the particular transformation of novel soft materials into a commercial product converging in the demonstration of the real the chemical, physical and thermodynamical factors that could potentially drive their successful transformation. </p> <p> </p> <p>First, this dissertation introduces the use of rotational and oscillatory shear rheometry to quantify the solvent evaporation effect on the flow behavior of polymer solutions used to fabricate isoporous asymmetric membranes. Three different A-B-C triblock copolymer were evaluated: polyisoprene-<i>b</i>-polystyrene-<i>b</i>-poly(4-vinylpyridine) (ISV); polyisoprene-<i>b</i>-polystyrene-<i>b</i>-poly(<i>N</i>,<i>N</i>-dimethylacrylamide) (ISD); and polyisoprene-<i>b</i>-polystyrene-<i>b</i>-poly(<i>tert</i>-butyl methacrylate) (ISB). The resulting evaporation-induced microstructure showed a solution viscosity and film viscoelasticity strongly dependent on the chemical structure of the triblock copolymer molecules. </p> <p> </p> <p>Furthermore, basic shear rheometry, flow birefringence, and advanced flow-velocimetry are used to deconvolute the flow-microstructure relationships of concentrated surfactant solutions. Sodium laureth sulfate in water (SLE₁S) was used to replicate spherical, worm-like, and hexagonally packed micelles and lamellar structures. Interesting findings demonstrated that regular features of flow curves, such as power-law shear thinning behavior, resulted from a wide variety of experimental artifacts that appeared when measuring microstructured fluids with shear rheometry.</p> <p> </p> <p>Finally, the successful integration of shear rheometry to calculate essential parameters to be used in a cost-effective visualization technique (still in development) used to calculate the dissolution time of polymers is addressed. The use of oscillatory rheometry successfully quantify the viscoelastic response of polyvinyl alcohol (PVA) solutions and identify formulations changes such as additive addition. The flow behavior of PVA solutions was correlated to dissolution behavior proving that the developed protocol has a high potential as a first screening tool.</p><br><p></p>