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A non-contact angular measurement system for Pitch Static Attitude (PSA) and Roll Static Attitude (RSA) of hard disk drive sliders is designed and built. Real-time sampling at over 15 KHz is achieved with accuracy of +/- 0.05 degrees over a range of approximately 2-3 degrees. Measuring the PSA and RSA is critical for hard drive manufacturers to control and improve the quality and reliability of hard drives. Although the hard drive industry is able to measure the PSA and RSA at the subassembly level at this time, there is no system available that is able to measure PSA/RSA at the final assembly level. This project has successfully demonstrated a methodology that the PSA/RSA can be reliably measured in-situ using a laser and position sensitive detector (PSD) technology. A prototype of the measurement system has been built using simple and inexpensive equipment. This device will allow a continuous measurement between the parked position on the ramp and the loading position just off of the disk surface. The measured data can be used to verify manufacturing processes and reliability data.

<p>Semiconductor laser diode has been a popular research topic for longer than half a century and plays a crucial role in optical communication systems. The work in this thesis focuses on the development of the semiconductor laser diode with rapid-evolving nanotechnologies: by incorporating specific semiconductor or metal structures in the nanometer scale into the laser cavity, several key advantages are achieved.</p> <p>One category of the nano-materials is semiconductor quantum dots (QD). QD laser is a promising product by providing three-dimensional confinement to the injected electrons and holes. However, in order to realize the single-longitudinal-mode operation, which is critical to optical communications in purpose of reducing the dispersion and partition noise, the Fabry-Perot (FP) QD laser still needs further development to suppress the gain-broadening effects; otherwise the mode-selective structure must be adopted, such as the distributed feedback (DFB) cavity. In this thesis, the QD FP laser and QD DFB laser are both researched by advanced modelling techniques and the work is summarized as follows.</p> <p>1) For the QD FP laser, a comprehensive rate-equation model has been applied for simulation, with the emphasis on describing the interplay of inhomogeneous and homogeneous gain-broadening effects. According to the laser-behaviour simulations, it is found that for each given inhomogeneous broadening, the optimum homogeneous broadening can be obtained for the single longitudinal-mode selectivity. Based on the optimal gain-broadening parameters, the single-mode QD FP laser is designed and analysed. The quantitative conditions for the performance feasibility are examined with respect to the gain-broadening parameters.</p> <p>2) A one-dimensional (1D) standing wave model is developed for the QD DFB laser. This model can provide more information for the laser operation and better describe the dynamic behaviour compared with the rate-equation model. Based on it, the statistic operation and output spectrum of a typical QD DFB laser are simulated; and then the dynamic properties of the laser are analysed.</p> <p>The other category is the metal nano-structure, including the metal nano-particle and the metal nano-strip Bragg grating. The related work is summarized as follows.</p> <p>1) The optical properties of a single metal nano-particle with different size, composition and shape are researched by Mie theory, with respect to the localized surface plasmon polariton (LSPP) effect. It shows that both the resonance wavelength and Q-factor can be tuned in a large scale by proper methods.</p> <p>2) A novel metal nano-strip distributed Bragg grating (DBR) laser is proposed and investigated theoretically. Firstly the metal nano-strip Bragg grating is simulated by the couple-mode theory and the mode-matching method. It shows that the coupling constant and reflection spectrum can be tuned to meet different requirements when varying the grating parameters. Then for the designed metal-grating DBR laser, the rate-equation simulation results show that it works under the single-mode operation for a broad range of the design parameters.<br /> <strong></strong></p> / Doctor of Philosophy (PhD)

L'interférométrie à rétro-injection optique, également connu sous le nom de Self-Mixing, permet de concevoir des capteurs qui sont compacts, auto-alignés et sans contact. Dans ce phénomène, une partie du faisceau laser de retour réfléchi par la cible rentre dans la cavité active de laser et fait varier ses propriétés spectrales. La diode laser agit alors comme une source de lumière, un microinterféromètre ainsi qu'un détecteur de lumière. Dans cette thèse, un capteur de déplacement, basé sur la rétro-injection optique, a été optimisé de sorte que des mesures précises peuvent être obtenues en temps réel. Le capteur est robuste à la disparition des franges de self-mixing pour des vibrations harmoniques. Il est également capable de s'adapter à un changement dans le régime de feedback optique et peut donc extraire le déplacement dans les cas les plus répandus expérimentalement, à savoir un feedback faible puis modéré. L'utilisation de l'optique adaptative, sous la forme d'une lentille liquide, a également été démontrée pour ce capteur, ce qui nous a permis de maintenir le capteur dans un régime de feedback favorable. L'influence du speckle a également été réduite de telle sorte que le capteur mesure jusqu'à la gamme centimétrique pour des cibles non- oopératives. Une nouvelle technique est également présentée, elle permet de rendre le capteur insensible aux vibrations mécaniques parasites qui fausseraient la mesure pour des conditions industrielles. / Optical Feedback Interferometry, also known as Self-Mixing, results in compact, selfaligned and contact-less sensors. In this phenomenon, a portion of the laser beam is back reflected from the target and enters the active laser cavity to vary its spectral properties. The laser diode then simultaneously acts as a light source, a micro- nterferometer as well as a light detector. In this thesis, a self-mixing displacement sensor has been optimised so that precise measurement can be obtained in real-time. The sensor is robust to the disappearance of self-mixing fringes for harmonic vibrations. It is also able to auto-adapt itself to a change in the optical feedback regime and so can extract displacement from the weak as well as moderate feedback regime signals. The use of adaptive optics, in the form of a liquid lens, has also been demonstrated for this sensor, which has allowed us to maintain the sensor in a fringe-loss less regime. The influence of speckle has also been reduced so that the sensor can now measure up to the centimetric range for non-cooperative targets. A novel technique has also been presented that makes the sensor insensitive to parasitic mechanical vibrations that would falsify the measurement under industrial conditions.

A disponibilização de fontes ópticas multi-comprimento de onda de baixo custo certamente é um dos aspectos fundamentais para viabilizar a implantação de redes WDMPON (Wavelength Division Multiplexing-Passive Optical Network). Na literatura, são encontradas propostas de algumas tecnologias para a construção de tais dispositivos como a utilização de fontes ópticas sintonizáveis, uso de um vetor de lasers DFB (Distributed Feedback Laser) ou, até mesmo, o fatiamento espectral de uma fonte de banda larga. Contudo, essas propostas apresentam custo elevado, ou limitações de operação, tornando-se inapropriadas para a aplicação de interesse. Uma alternativa que vem sendo amplamente utilizada é o travamento óptico de diodos laser de Fabry-Pérot (FP-LD - Fabry-Pérot laser diode), realizado por meio da injeção de sinal óptico externo provindo do fatiamento espectral de uma fonte de banda larga. O travamento óptico possibilita o controle espectral do FP-LD, e o seu baixo custo torna essa fonte óptica atrativa na implantação de redes WDM. O entendimento do mecanismo de travamento torna-se, então, crucial na descrição da dinâmica de tais fontes ópticas. Desta forma, nesta dissertação, foi desenvolvido o estudo dos modelos matemáticos que descrevem a dinâmica de lasers travados, assim como foi investigado o desempenho de redes WDM-PON empregando estas fontes ópticas. / The availability of low cost multi-wavelength optical sources is certainly one of the fundamental aspects to allow the deployment of WDM-PON networks. Several technologies for the implementation of such optical sources are discussed in the literature, including tunable lasers, DFB arrays and spectral slicing of a broadband light source. However, those propositions suffer from high cost or operational limitations. One alternative is the optical injection locking of a Fabry Pérot laser diode (FPLD), in which the external optical injection signal is obtained from the spectral slicing of a broadband light source. This option has been widely investigated because the optical injection locking process allows for the FP-LD optical spectral control and wavelength selection. In addition, the low cost of such device makes this optical source an attractive solution for WDM-PON widespread deployment. In this context, the understanding of the locking mechanism becomes important in the optimization of such optical sources. Thus, in this dissertation, we conducted a study of mathematical models that describe the dynamics of locked lasers as well as investigated the performance of WDM-PON based on those optical sources.

The material and device characteristics of InGaN/GaN heterojunction bipolar transistors (HBTs) grown by metalorganic chemical vapor deposition are examined. Two structures grown on sapphire with different p-InxGa1-xN base-region compositions, xIn = 0.03 and 0.05, are presented in a comparative study. In a second experiment, NpN-GaN/InGaN/GaN HBTs are grown and fabricated on free-standing GaN (FS-GaN) and sapphire substrates to investigate the effect of dislocations on III-nitride HBT epitaxial structures. The performance characteristics of HBTs on FS-GaN with a 20×20 m2 emitter area exhibit a maximum collector-current density of ~12.3 kA/cm2, a D.C. current gain of ~90, and a maximum differential gain of ~120 without surface passivation. For the development of deep-ultraviolet optoelectronics, several various structures of optically-pumped lasers at 257, 246, and 243 nm are demonstrated on (0001) AlN substrates. The threshold-power density at room temperature was reduced to as low as 297 kW/cm2. The dominating polarization was measured to be transverse electric in all cases. InAlN material was developed to provide lattice matched, high-bandgap energy cladding layers for a III-N UV laser structure. This would alleviate strain and dislocation formation in the structure, and also mitigate the polarization charge. However, a gallium auto-doping mechanism was encountered which prevents the growth of pure ternary InAlN, resulting instead in quaternary InAlGaN. This phenomenon is quantitatively examined and its source is explored.

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-10-10T17:10:14Z No. of bitstreams: 1 CICERO MOEZIO DA SILVA – DISSERTAÇÃO (PPGFísica) 2013.pdf: 1359216 bytes, checksum: 450c592c37b5fc9ef90ce40e270eaaae (MD5) / Made available in DSpace on 2018-10-10T17:10:14Z (GMT). No. of bitstreams: 1 CICERO MOEZIO DA SILVA – DISSERTAÇÃO (PPGFísica) 2013.pdf: 1359216 bytes, checksum: 450c592c37b5fc9ef90ce40e270eaaae (MD5) Previous issue date: 2013-08-16 / Capes / Este trabalho reporta o desenvolvimento experimental de um sistema de travamento da frequência de um diodo laser nas asas de uma linha atômica. Como sinal de erro, utilizamos a transmissão por uma célula com janelas paralelas (contendo vapor de césio) para o travamento da frequência. Mostramos que o sinal de erro é estável durante 1 hora e meia. Este sinal contemos citações nas asas da ressonância que podem ser usadas para a estabilização da frequência. Travamos a frequência entre 1860 a 2817 MHz fora da ressonância e obtemos uma estabilidade de 30MHz. A técnica descrita não necessita de campo magnético ou de detecção sensível a polarização,que simplifi ca substancialmente em relação às técnicas existentes. / In this work we demonstrate the experimental development of a system of frequency- locking of a diode laser on the wings of an atomic line. As an error signal, we use the transmission through a cell with parallel windows (containing cesium vapor) for the frequency-locking. We show that the error signalis stable for one hour and a half and has oscillations in the wings of the resonance that can be used tostabilize the frequency. We locked the frequency between 1860-2817 MHz out of resonance and obtained a stability of 30MHz. The described technique does not require a magnetic field or polarization-sensitive detection, whichs impli es substantially over existing techniques.

Le niveau de sécurité requis dans l'aviation civile a conduit à l'utilisation de plusieurs chaînes séparées de mesures pour une même information. Il est désormais recommandé de les compléter par une chaîne de mesure dissemblable. Ainsi, THALES Avionics développe depuis 2006 un anémomètre laser dont l'injecteur est réalisé en optique intégrée sur verre pour la mesure de la vitesse de l'avion. Ce travail de thèse vise à poursuivre la miniaturisation en hybridant sur une puce de verre la diode laser de pompe qui alimente l'injecteur optique. L'architecture proposée repose sur le verrouillage d'une diode laser à ruban large sur son mode fondamental grâce à une cavité externe planaire. Celle ci est constituée d'un convertisseur modal réalisé par échange d'ions sur verre intégrant un réseau de Bragg à sa sortie monomode. Le travail réalisé dans cette thèse comporte trois étapes principales. Dans un premier temps, un modèle analytique a permis de dimensionner la rétroaction optique à imposer sur la diode. L'échange d'ions sélectivement assisté par champ électrique a permis dans un second temps de réaliser un convertisseur modal adapté à la liaison entre la diode ruban et la fibre optique monomode de récupération. Finalement, le verrouillage modal a été démontré grâce à l'utilisation d'une fibre optique à réseau de Bragg. L'émission spectrale de la diode laser a été stabilisée autour de la longueur d'onde de Bragg sur une largeur spectrale de 0,3 nm tandis que la puissance en sortie de la fibre monomode a atteint 100 mW. Le réseau de Bragg a alors été intégré sur la puce optique et l'émission de la diode laser ruban a également été stabilisée par la rétroaction intégrée. La forte réflexion du réseau a limité la puissance en sortie du dispositif et une émission sur deux modes transverses a été constatée. Les perspectives de cette étude portent, d'une part, sur l'augmentation de la puissance en sortie du dispositif et, d'autre part, sur la réalisation d'un système de pompage monolithique d'un milieu actif placé au sein de la cavité externe. / Objectives of security in civil aviation are reached in multiplying separated measuring chains. The use of dissimilar measuring chains is now encouraged. For this purpose, THALES Avionics has developed an aircraft speed laser anemometer. The suitability of integrated optics on glass for the miniaturisation of the system has been proven in 2006. This thesis aims at pushing ahead with the miniaturisation in hybridising the pump laser diode which supplies the seed laser on a glass platform. The structure consists on locking the fundamental of a Broad Area Laser Diode (BALD) thanks a planar external cavity, composed of a modal converter made by ion exchange on glass and a Bragg grating. First, easy to use conception rules for the BALD's optical feedback are elaborated. Then, the technique of selective field assisted ion exchange is shown to be adapted to the realisation of a modal converter between the BALD and a single mode collecting optical fibre. The realised converter demonstrated the modal locking thanks to the use a fibre Bragg grating. The BALD has been stabilized around the Bragg wavelength with a spectral width of 0.3 nm and stable single mode output power has reached 100 mW. The Bragg grating has then been integrated on the optical chip and the integrated locking of the BALD has been achieved. The output power has been limited by the high reflectivity of the grating. As perspectives, the increase of the output power has been studied and a highly integrated system of intra cavity pumping is proposed.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Vision, the human being s favorite sense, and its great capacity to obtain, to process and to interpret great amount of visual nature data has been throughout the years a great inspiration for development of techniques and technological devices that reproduce it into a computational system. In welding processes, vision can supply information in inspection and welded joint s quality, in the parameters monitoring, in trajectory correction and even, finally, in the study of the phenomena involved in the process. However, the luminosity/radiation emitted from the weld arc represents a barrier for these studies based in the process visualization. One of the forms currently used to visualize the process, without the interference of the arc s light, consists of illuminating the process with the near infrared light and, using band pass (interference) filters, around this exactly wave length, during the acquisition of the images. A solution for the near infrared illumination, of increasing application, involves the use of laser diodes of high power, with low cost and less complex installation than conventional lasers. Therefore, the proposal of this work is the project, construction and assessment of a vision system for welding processes with low cost and high flexibility. It is based on characterization of the spectrum of the weld arc, definition of a drive topology for the laser diode within its limitations of use and maximizing the emitted luminous power, built of control circuits, selection of optics equipment and components and, finally, project and application of a prototype for visualization of different arc-welding processes. The electrical system was validated by computational simulations and experimental burnout and stress tests. The final assessment of the whole vision system was carried out during TIG and MIG/MAG welding. Although, during the welding, the system was not capable of overcome the arc radiation, it provides a homogenous illumination in synchronism with the camera, which represents the main limitation due to its large shutter. Eventually, it s suggested to employ the developed vision system for helping joint tracking. / A visão, o sentido predileto do ser humano, e sua grande capacidade de captar, processar e interpretar grandes quantidades de dados de natureza visual tem sido, ao longo dos anos, um grande estímulo para o desenvolvimento de técnicas e de dispositivos tecnológicos que a reproduzam um sistema computacional. Nos processos de soldagem, a visão pode fornecer dados desde na inspeção e qualidade da junta soldada, no monitoramento de parâmetros, na correção de trajetórias até, por fim, no estudo dos fenômenos envolvidos no processo. Porém, a radiação luminosa emitida pelo arco representa uma barreira para tais estudos baseados na visualização do processo. Uma das formas utilizadas atualmente para se obter a visualização do processo, sem a interferência do arco, consiste em iluminar o processo com o infravermelho próximo e utilizar filtros de interferência (passa-faixa), em torno deste mesmo comprimento de onda, durante a aquisição das imagens. Uma solução para a iluminação infravermelha, de aplicação crescente, envolve o uso de diodos laser de alta potência, com baixo custo e menor complexidade de instalação do que os lasers convencionais. Desta forma, a proposta deste trabalho foi a criação de um sistema de visão dos processos de soldagem a arco, de baixo custo e alta flexibilidade, indo desde a caracterização dos espectros de emissão luminosa do arco, passando pela criação de uma topologia de acionamento para o diodo de alta potência no infravermelho próximo, respeitando suas limitações de uso e maximizando a potência luminosa emitida, criação dos circuitos de controle, escolha dos equipamentos e componentes ópticos e, por fim, projeto e aplicação de um protótipo em processos de soldagens. O sistema elétrico foi validado por simulações computacionais e testes experimentais de burnout e de stress, e as limitações do sistema de visão, como um todo, foram encontradas através e sua aplicação com soldagens TIG e MIG/MAG. Nestes ensaios, embora não tenha sido capaz de sobrepor a luz do arco, o sistema desenvolvido proporcionou uma iluminação homogênea e em sincronia com a câmera, onde a principal limitação foi o grande tempo de exposição da câmera disponível. Sugere-se, ao final, utilizar o sistema na forma de um seguidor de juntas. / Mestre em Engenharia Mecânica

A disponibilização de fontes ópticas multi-comprimento de onda de baixo custo certamente é um dos aspectos fundamentais para viabilizar a implantação de redes WDMPON (Wavelength Division Multiplexing-Passive Optical Network). Na literatura, são encontradas propostas de algumas tecnologias para a construção de tais dispositivos como a utilização de fontes ópticas sintonizáveis, uso de um vetor de lasers DFB (Distributed Feedback Laser) ou, até mesmo, o fatiamento espectral de uma fonte de banda larga. Contudo, essas propostas apresentam custo elevado, ou limitações de operação, tornando-se inapropriadas para a aplicação de interesse. Uma alternativa que vem sendo amplamente utilizada é o travamento óptico de diodos laser de Fabry-Pérot (FP-LD - Fabry-Pérot laser diode), realizado por meio da injeção de sinal óptico externo provindo do fatiamento espectral de uma fonte de banda larga. O travamento óptico possibilita o controle espectral do FP-LD, e o seu baixo custo torna essa fonte óptica atrativa na implantação de redes WDM. O entendimento do mecanismo de travamento torna-se, então, crucial na descrição da dinâmica de tais fontes ópticas. Desta forma, nesta dissertação, foi desenvolvido o estudo dos modelos matemáticos que descrevem a dinâmica de lasers travados, assim como foi investigado o desempenho de redes WDM-PON empregando estas fontes ópticas. / The availability of low cost multi-wavelength optical sources is certainly one of the fundamental aspects to allow the deployment of WDM-PON networks. Several technologies for the implementation of such optical sources are discussed in the literature, including tunable lasers, DFB arrays and spectral slicing of a broadband light source. However, those propositions suffer from high cost or operational limitations. One alternative is the optical injection locking of a Fabry Pérot laser diode (FPLD), in which the external optical injection signal is obtained from the spectral slicing of a broadband light source. This option has been widely investigated because the optical injection locking process allows for the FP-LD optical spectral control and wavelength selection. In addition, the low cost of such device makes this optical source an attractive solution for WDM-PON widespread deployment. In this context, the understanding of the locking mechanism becomes important in the optimization of such optical sources. Thus, in this dissertation, we conducted a study of mathematical models that describe the dynamics of locked lasers as well as investigated the performance of WDM-PON based on those optical sources.