No description available.

No description available.

No description available.

No description available.

Interference between the modes of an optical fiber results in specific intensity patterns which can be modulated as a function of disturbances in the optical fiber system. These modulation effects are a direct result of the difference in propagation constants of the constituent modes. In this presentation it is shown how the modulated intensity patterns created by the interference of specific mode groups in few-mode optical fibers (V < 5.0) can be used to detect strain. A detailed discussion of the modal phenomena responsible for the observed strain induced pattern modulation is given and it is shown that strain detection sensitivities on the order of 10-9 can be expected. Data taken during the evaluation of an actual experimental strain detection system based on the developed theory is also presented. / Master of Science

No description available.

Attenuated total reflection techniques have been used extensively as analytical tools for the analysis of thin films and analytes imbedded in complex scattering matrices. However they have not been commonly utilized as detectors in common analytical techniques such as Flow Injection Analysis because of their relatively low sensitivity. The feasibility of using a thin film planar waveguide as an absorption sensor in the Flow Injection Analysis of Urea was investigated. Urea was hydrolyzed to ammonia and carbon dioxide with the enzyme Urease. The ammonia produced was quantitated colorimetrically using Berthelot’s reaction. The reaction product, indophenol blue, was detected using the combination planar waveguide 9.2 microliter flow cell sensor. The planar waveguides used had 2 to 3 orders of magnitude greater sensitivity than typical internal reflection elements. The analytical working range obtained for urea determinations was from 0 to 20 mM urea at a rate of 30 samples per hour. A description of the investigation and the various factors involved in designing and optimizing a planar waveguide for absorption spectrometry is included. / Ph. D.

The scattering of acoustic waves by boundary discontinuities in waveguides is analyzed using the Method of Matched Asymptotic Expansions (MAE). Existing theories are accurate only for very low frequencies. In contrast, the theory developed in this thesis is valid over the entire range of frequencies up to the first cutoff frequency. The key to this improvement lies in recognizing the important physical role of the cutoff cross-modes of the waveguide, which are usually overlooked. Although these modes are evanescent, they contain information about the interaction between the local field near the discontinuity and the far-field. This interaction has a profound effect on the far-field amplitudes and becomes increasingly important with frequency. The cutoff modes also present novel mathematical problems in that current asymptotic techniques do not offer a rational means of incorporating them into a mathematical description. This difficulty arises from the non-Poincare form of the cross-modes, and its resolution constitutes the second new result of this thesis. We develop a matching scheme based on block matching intermediate expansions in a transform domain. The new technique permits the matching of expansions of a more general nature than previously possible, and may well have useful applications in other physical situations where evanescent terms are important. We show that the resulting theory leads to significant improvements with just a few cross-mode terms included, and also that there is an intimate connection with classical integral methods. Finally, the theory is extended to waveguides with slowly varying shape. We show that the usual regular perturbation analysis of the wave regions must be completely abandoned. This is due to the evanescent nature of the cross-modes, which must be described by a WKB approximation. The pressure field we so obtain includes older results. The new terms account for the cutoff cross-modes of the variable waveguide, which play a central role in extending the dynamic range of the theory. / Ph. D.

La chirurgie par stimulation profonde (DBS) est une option de traitement pour les patients atteints de la maladie de Parkinson. Cette procédure implique l'implantation d'électrodes dans certaines régions spécifiques du cerveau qui sont impliquées dans le contrôle des mouvements. Bien que la chirurgie par stimulation profonde ne guérisse pas la maladie de Parkinson, elle peut considérablement améliorer la qualité de vie des patients en réduisant les symptômes moteurs tels que la bradykinésie (lenteur anormale dans l'exécution des mouvements volontaires), le tremblement de repos et la rigidité musculaire, tout en augmentant leur capacité à effectuer les activités quotidiennes. La problématique est qu'il est difficile d'atteindre la cible de manière optimale à cause d'un possible déplacement cérébral à la suite de l'ouverture de la boite crânienne lors de la chirurgie. Il y a donc un besoin urgent de développer et d'améliorer les techniques de neuronavigation pour optimiser le positionnement des électrodes lors de la chirurgie DBS. Ces avancées permettraient de guider la procédure en temps réel avec une précision accrue, en intégrant des technologies innovantes capables de compenser les déplacements cérébrales survenant au cours de la chirurgie. Une amélioration du positionnement des électrodes se traduirait par des bienfaits cliniques accrus, notamment une réduction plus efficace des symptômes moteurs de la maladie de Parkinson et une diminution des effets secondaires liés à un positionnement inapproprié. L'objectif principal du présent projet de maîtrise est de modifier une électrode DBS en intégrant des fibres optiques capables de réaliser de la spectroscopie par réflexion diffuse (DRS) afin d'améliorer le positionnement des électrodes. La modification du dispositif amène des questions sur l'intégrité mécanique de la nouvelle structure, la sécurité en général de la conception et la qualité des informations transmises par les fibres optiques. Ce projet de maîtrise est un défi multidisciplinaire, passant par des analyses des propriétés mécaniques de la sonde et la pertinence du concept du DRS sur des tissus cérébraux frais. / Deep Brain Stimulation (DBS) surgery is a treatment option for patients with Parkinson's disease. This procedure involves implanting electrodes into specific regions of the brain that are involved in motor control. While DBS does not cure Parkinson's disease, it can significantly improve patients' quality of life by reducing motor symptoms such as bradykinesia (abnormally slow execution of voluntary movements), resting tremor, and muscular rigidity, while enhancing their ability to perform daily activities. However, achieving optimal targeting during surgery is challenging due to potential brain shift following the opening of the skull. There is therefore an urgent need to develop and enhance neuronavigation techniques to optimize electrode positioning during DBS surgery. These advancements would allow for real-time guidance with increased precision, integrating innovative technologies capable of compensating for brain shifts occurring during the procedure. Improved electrode positioning would result in greater clinical benefits, including more effective reduction of Parkinson's motor symptoms and a decrease in side effects associated with improper positioning. The primary objective of this master's project is to modify a DBS electrode by integrating optical fibers capable of performing diffuse reflectance spectroscopy (DRS) to improve electrode positioning. This modification raises critical questions regarding the mechanical integrity of the new structure, the overall safety of the design, and the quality of the information transmitted by the optical fibers. This multidisciplinary project involves analyzing the mechanical properties of the probe and validating the relevance of the DRS concept through tests on fresh brain tissues.

Dans un contexte de changements climatiques, des capteurs de méthane abordables, mais performants et autonomes sont requis pour surveiller les émissions et quantifier les concentrations de ce puissant gaz à effet de serre dans l’atmosphère des régions éloignées, comme les milieux nordiques. Une solution prometteuse pour répondre à ce besoin provient de la photonique sur silicium, une plateforme d’optique intégrée. Les guides d’onde intégrés sont un composant essentiel pour la détection sur puce par spectroscopie d’absorption, où ils jouent le double rôle de routage et de transducteur. Ainsi, ce projet vise à améliorer les performances du guide d’onde nécessaire à cette application. Des guides d’onde en réseaux sous-longueur d’onde(SWG) opérant en régime de lumière lente sont proposés pour améliorer l’interaction lumière matière. Leur segmentation périodique a comme effet qu’une large fraction de la lumière se propage dans l’air, le milieu d’intérêt à sonder. De plus, il est démontré que la périodicité de la structure, lorsque proche, mais inférieure à la moitié de la longueur d’onde, produit un effet de lumière lente ; c’est-à-dire que la vitesse de la lumière guidée diminue alors fortement. Leurs pertes de propagation et leurs indices de groupe sont ensuite caractérisés et comparés à des guides d’onde en ruban conventionnels à titre de référence. Bien que les guides d’onde SWG possèdent un facteur d’interaction supérieur aux guides d’onde en ruban, leurs pertes de propagation plus élevées limitent leurs performances. Les guides d’onde en ruban sont donc la meilleure option pour cette application, en plus d’être mécaniquement plus robustes et faciles à concevoir et fabriquer. Des efforts de détection sur puce avec ces derniers ont été réalisés, mais la présence de franges d’interférence est le facteur limitant malgré l’application d’une technique de traitement de signal pour les atténuer. D’autres méthodes sont proposées pour améliorer le rapport signal sur bruit. Finalement, il est démontré expérimentalement que les guides d’onde SWG peuvent supporter un régime de lumière lente. Un indice de groupe maximal de 30 est obtenu et celui-ci est aisément accordable, autant en amplitude qu’en position spectrale, ouvrant la voie à diverses autres applications pour ce type de guide d’onde. / In the context of climate change, affordable, but effective and autonomous methane sensors are required to monitor the emissions and the concentration of this potent greenhouse gas in the atmosphere of remote areas, like in northern environments. A promising solution to this need comes from silicon photonics, an integrated optics platform. Integrated waveguides are an essential component for on-chip detection by absorption spectroscopy, where they play the dual role of routing and transducer. Thus, this project aims at improving the performance of the waveguide for this application. The use of slow-light subwavelength grating waveguides (SWG) is proposed to enhance the light-matter interaction. Their periodic segmentation has the effect that a large fraction of the light is propagating through the air, the medium of interest to probe. In addition, we show that the periodicity of the structure, when close but less than half the wavelength, produces the slow-light effect; i.e. the speed of guided light drops sharply. Their propagation losses and their group index are then characterized and compared to conventional strip waveguides for reference. Although the SWG waveguides have an interaction factor greater than strip waveguides, their higher propagation loss limit their performances. Strip waveguides are therefore chosen for further investigation for the sensor application., in addition to being mechanically robust, and easier to design and fabricate. Efforts for on-chip detection of methane have been made with strip waveguides, but the presence of interference fringes is the limiting factor despite the application of a signal processing technique to mitigate them. Other methods are proposed to improve the signal to noise ratio. Finally, we experimentally show that SWG waveguides can support a slow-light regime. A maximum group index of 30 is obtained and it is easily tunable, in both amplitude or wavelength, paving the way for various other applications for this type of waveguide.