Tese de mestrado. Engenharia Electrotécnica e de Computadores. 2006. Faculdade de Engenharia. Universidade do Porto, Faculdade de Ciências

Tese de mestrado. Faculdade de Engenharia. Universidade do Porto. 1998

Zugl.: Dresden, Techn. Univ., Habil.-Schr., 2007

Thesis (M.S.)--University of Wisconsin--Madison, 1960. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 285-292).

M.Ing. / Bragg gratings written in polymer optical fibres are much more sensitive to temperature and strain measurements than silica fibre with a lower Young's modules and higher temperature coefficient. The good biocompatibility of polymer fibres makes them ideal medical sensors for in vivo strain and temperature measurements as well as excellent chemical sensors that can easily be doped with organic compounds. Most of the Bragg gratings in polymer optical fibres are inscribed around 1550 nm where the attenuation is as large as 1 dB/em. Grating fabrication was investigated at 980 nm where the attenuation was discovered to be optimal (less than 0.1 dB/em). The polymer optical fibre was spliced to silica optical fibre through butt-coupling and affixed with optical adhesive to produce transmission loss of between 7 and 25 dB (at 980 nm). Preliminary results show that it may be possible to create fibre Bragg gratings in polymer optical fibre at 980 nm. Gratings inscribed in fibre with an energy density of between 80 and 150 mJ/cm2 supplied by Paradigm Optics (MORFOP3) had a repeatability of 25%. With the fibres supplied by Prof. Peng (PBzMA- PEMA- PMMA co-polymer) a success rate of more than 90% was achieved when using energy densities around 70 mJ/cm2 • However, these gratings were weak and disappeared within 48 hours. The strength of these gratings varied from grating to grating. The reason of this instability is unknown and should be further investigated. The temperature sensitivity of polymer optical fibre at 976 nm was found to be -100 ±17 pm;oc corresponding with the reported value of -94 pm;oc at 976 nm.

Récemment, de nouvelles techniques ont été développées pour la fabrication des réseaux de Bragg à profil complexe. Ces composants photoniques sont utilisés dans plusieurs applications émergentes telles que la compensation de la dispersion pour les systèmes de communication de longue portée, les lasers à fibre, multiplexeurs et détecteurs optiques. Le diagnostic après inscription devrait fournir les informations nécessaires pour l’amélioration de la fabrication des réseaux de Bragg. Nous savons que les propriétés spectrales du réseau de Bragg sont liées au profil d’indice Δn. Les techniques de mesure directes, telles que la diffraction latérale de Krug, permettent de retrouver l’amplitude de modulation d’indice le long du réseau. Cependant, ces techniques sont insensibles aux fluctuations de phase. Une méthode alternative de caractérisation indirecte fondée sur l’algorithme de Layer-Peeling (LP) a été proposée. Toutefois elle ne peut pas être appliquée à la caractérisation des réseaux longs en raison de la propagation du bruit de calcul. Dans cette thèse nous avons présenté une nouvelle technique pour la mesure directe de l’amplitude et de la phase du profil d’indice le long du réseau de Bragg fondée sur la luminescence bleue (LB) induite par l’irradiation UV. Nos résultats expérimentaux de la mesure du profil de modulation d’indice sont en bonne correspondance avec la méthode de Krug. La méthode que nous proposons peut être appliquée à la caractérisation des réseaux longs. Elle permet de retrouver simultanément l’amplitude de modulation d’indice Δnac(z), la fonction du chirp et détecter le changement de l’indice moyen Δndc(z). / N the last decade new techniques were developed for fabrication of sophisticated Fiber Bragg Gratings (FGBs). This has been motivated by the emergence of many applications such as dispersion compensation for long-haul communication systems, DFB fiber lasers, optical add/drop multiplexers, and optical sensors. Post-fabrication diagnostics should provide relevant information to enhance the FBG fabrication process. It is well known that the FBG spectral properties are related to the index profile Δn. Direct measurement techniques, such as the side diffraction method reported by P. Krug, allow determining the index modulation amplitude along the FBG. Nevertheless, these techniques provide no information about phase fluctuations. An alternative method of indirect characterization, based on the Layer-Peeling (LP) algorithm, consists in Bragg grating profile reconstruction from its complex reflectivity. However, the LP method is unstable when applied to characterize long FBGs (>1mm) due to the error propagation effect. In this thesis we have shown the principle of a novel technique for the direct measurement of amplitude and phase variations of the index modulation along an FBG based on the blue luminescence (BL). Our experimental results are in a good agreement with the according Krug characterization. The proposed method of FBG characterization in amplitude and phase using the UV induced BL can be applied to long gratings (up to tens of centimeters) having complex index modulation profiles. It allows retrieving simultaneously the index profile modulation Δnac(z) and the chirp function, localizing phase shifts, and also detecting the mean index change Δndc(z).

L'avènement de la photonique intégrée a attiré beaucoup de recherche et d'attention industrielle au cours des deux dernières décennies, plusieurs croyant qu'il s'agit d'une révolution équivalente à la microélectronique. Tout en tirant parti des procédés de fabrication de masse hérités de la microélectronique, la photonique sur silicium est compacte, éconergitique et permet l'intégration complète de dispositifs et de circuits photoniques à l'échelle nanométrique pour des applications cruciales dans les télécommunications, la détection et le calcul optique. À l'instar des débuts de la microélectronique, les efforts de recherche actuels en photonique sur silicium sont principalement consacrés à la proposition, à la conception et la caractérisation de composants standardisés en vue d'une éventuelle intégration de masse dans des circuits photoniques. Les principaux défis associés à ce développement comprennent la complexité de la théorie électromagnétique dans le fonctionnement des dispositifs, les variations et les non-uniformités du procédé de fabrication limitant les performances, et les ressources informatiques considérables nécessaires pour modéliser avec précision des circuits photoniques complexes. Dans ce mémoire, ces trois limitations sont abordées sous forme de contributions de recherche originales. Basées sur des dispositifs photoniques sur silicium et l'apprentissage machine, les contributions de ce mémoire concernent toutes les réseaux de Bragg intégrés, dont le principe de fonctionnement de base est la réflexion optique sélective en fréquence. Premièrement, un nouveau filtre optique double-bande basé sur les réseaux de Bragg multimodes est introduit pour des applications dans les télécommunications. Deuxièmement, une nouvelle architecture de filtre accordable basée sur un coupleur contra-directionnel à étage unique avec un dispositif de micro-chauffage segmenté permettant des profils de température arbitraires démontre une accordabilité de la bande passante record et des capacités de compensation des erreurs de fabrication lorsqu'opérée par un algorithme de contrôle. Troisièmement, un modèle d'apprentissage machine basé sur un réseau de neurones artificiels est introduit et démontré pour la conception de coupleurs contra-directionnels et le diagnostic de fabrication, ouvrant la voie à la production de masse de systèmes photoniques intégrés basée sur les données. / The advent of integrated photonics has attracted a lot of research and industrial attention in the last two decades, as it is believed to be a hardware revolution similar to microelectronics. While leveraging microelectronics-inherited mass-production-grade fabrication processes for full scalability, the silicon photonic paradigm is compact, energy efficient and allows the full integration of nano-scale optical devices and circuits for crutial applications in telecommunications, sensing, and optical computing. Similar to early-day microelectronics, current research efforts in silicon photonics are put toward the proposal, design and characterization of standardized components in sights of eventual black-box building block circuit design. The main challenges associated with this development include the complexity of electromagnetic theory in device operation, the performance-limiting fabrication process variations and non-uniformities, and the considerable computing resources required to accurately model complex photonic circuitry. In this work, these three bottlenecks are addressed in the form of original research contributions. Based on silicon photonic devices and machine learning, the contributions of this thesis pertain to integrated Bragg gratings, whose basic operating principle is frequency-selective optical transmission. First, a novel dual-band optical filter based on multimode Bragg gratings is introduced for applications in telecommunications. Second, a novel tunable filter architecture based on a single-stage contra-directional coupler with a segmented micro-heating device allowing arbitrary temperature profiles demonstrates record-breaking bandwidth tunability and on-chip fabrication error compensation capabilities when operated by a control algorithm. Third, an artificial neural network-based machine learning model is introduced and demonstrated for large-parameter-space contra-directional coupler inverse design and fabrication diagnostics, paving the way for the data-driven mass production of integrated photonic systems.

No description available.

This thesis details the design, fabrication and measurement of an integrated optical Bragg grating filter, operating at a free space wavelength of 1532 nm, based on silicon-on-insulator (SOI) ridge waveguide. Grating-based integrated devices can interact with optical signals in photonic integrated circuits (PIC) in such a way as to selectively transmit, reflect or detect the signals that are resonant with these devices. Channel filters can access one channel of a wavelength division multiplexed signal without disturbing the other channels and are therefore important elements in WDM communications. Resonator filters are attractive candidates because they can potentially realize the narrowest linewidth for a given device size. Device models for this kind of device are developed by using the MATLAB programming language. Coupled mode theory (CMT) for filters, and the effective index method (EIM) which reduces a three dimensional (3D) analysis into two dimensions is used as modeling theoretical background. Computer modeling identifies the effect of device structure on the performance of the devices, and is also used to predict the output characteristics of this kind of device. This provides an understanding of device physics and operation, and a basis for comparison with experimental results. A common fabrication sequence for integrated optical Bragg grating filters based on SOI ridge waveguides is designed, developed and demonstrated. This includes the photomask for optical ridged waveguide, interferometic lithography for grating pattern and high accuracy RIE etching. This work demonstrates Bragg grating as a technology for realizing PIC in SOI material system, and presents the technology required to design, fabricate, characterize, and model these integrated devices. / Thesis / Master of Applied Science (MASc)

Tese de mestrado integrado. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 2010