O objetivo do presente trabalho foi o estudo e análise da resposta óptica de dispositivos de cristal fotônico uni-dimensional (1D) fabricados através do uso da tecnologia de silício poroso. Os resultados obtidos neste trabalho apresentam contribuições significativas no desenvolvimento de uma tecnologia para a fabricação de dispositivos ópticos em silício. As principais contribuições deste trabalho estão direcionadas ao aprimoramento dos processos de fabricação de cristais fotônicos 1D e processos de tratamento térmico. Os resultados da análise estrutural através de microscopia óptica de varredura (MEV) e da resposta óptica (refletância ou absorbância) mostraram que dispositivos de cristal fotônico fabricados em soluções altamente diluídas de HF apresentam melhor desempenho, tendo sido otimizado o processo de fabricação utilizando-se uma célula de duplo compartimento (célula dupla). A otimização da resposta óptica dos dispositivos foi atribuída ao efeito de minimização das rugosidades de interface e minimização de efeitos de anisotropia na taxa de corrosão durante o processo de anodização eletroquímica. O processo eletroquímico utilizado para a fabricação de cristais fotônicos 1D apresentou limitação quanto ao número máximo de camadas, sendo observado que dispositivos com número de camadas acima de 60 apresentavam degradação das suas camadas superficiais, comprometendo a resposta óptica do dispositivo. Este resultado foi atribuído a efeitos de diluição química das camadas expostas à solução por longos períodos de processo. Os dispositivos fotônicos 1D mostraram-se sensíveis a processos de recozimento térmico, deslocando suas bandas fotônicas proibidas para regiões de menor comprimento de onda devido à mudança do índice de refração das camadas e aos efeitos de expansão e compressão das camadas constitutivas do dispositivo. Os dispositivos de micocavidade Fabry-Perot mostraram-se mais sensíveis aos processos de recozimento térmico. Os resultados obtidos no presente trabalho vislumbram grandes possibilidades de aplicação dos cristais fotônicos de PS na fabricação de dispositivos ópticos na tecnologia de silício como filtros, lentes, cavidades ressonantes, guias de ondas, grades de difração e dispositivos sensores. / The aim of the present work was to study and analyze the optical response of one- dimensional (1D) photonic crystal devices obtained by using the porous silicon technology. The experimental results obtained from this work showed the significant contribution to the development of a technological process for optical device fabrication in the silicon substrate. The most important contributions of the work are pointed out to improve the electrochemical process for device fabrication and thermal annealing process in order to improve the optical response of the devices. The results obtained from Scanning electronic microscopy (SEM) and from the optical response of the devices, showed that devices fabricated in the double cell and diluted HF solution improved their optical response due to minimization of the anisotropy of corrosion rate and decreasing of the surface roughness between layers. The electrochemical process used for device fabrication showed the existence of limitation on the numbers of layers because of the existence of chemical dissolution effect that became important for long time process. The 1D photonic crystal devices in PS technology showed high sensibility to thermal annealing process, due to the refraction index change after thermal annealing the photonic band gap position shift down to low wavelength region. The Fabry-Perot devices showed higher sensibility to thermal annealing process improving their optical response after annealing process. The results obtained from the present work showed that the PS 1D photonic device could be applied to optical devices fabrication in silicon technology such as optical filters, lenses, resonant cavities, wave-guide devices, diffraction grade and optical sensor device.

Este trabalho apresenta o projeto de pesquisa desenvolvido para a obtenção do título de Mestre em Engenharia Elétrica, na área de concentração de engenharia de sistemas, da Escola Politécnica da Universidade de São Paulo. O principal objetivo deste trabalho foi o desenvolvimento de um sistema de acionamento (driver) para os atuadores piezoelétricos do interferômetro de Fabry-Pérot do espectrômetro BTFI (Brazilian Tunable Filter Imager), um instrumento visitante do telescópio SOAR (Southern Astrophysical Research Telescope), no Chile. O Fabry-Pérot é um instrumento óptico composto de duas superfícies paralelas altamente reflexivas (espelhos), cuja distância é controlada por um sistema de nanoposicionamento composto de três atuadores piezoelétricos (piezos) do tipo APA® (Amplified Piezoelectric Actuators) e um sistema de medida capacitivo. O principal requisito técnico de desempenho do sistema de nanoposicionamento do Fabry-Pérot é tal que o ruído de posicionamento dos espelhos deve ser limitado a 3 . No entanto, os fenômenos não lineares de histerese e escorregamento (creep) dos piezos limitam a precisão de posicionamento do sistema de controle, razão pela qual foi desenvolvido um sistema de acionamento por carga e tensão para os piezos, com o intuito de atenuar suas não linearidades e, consequentemente, melhorar o desempenho do sistema de controle em malha fechada, em termos de ruído de posicionamento. A primeira etapa deste trabalho consistiu da caracterização do modelo e da instrumentação do sistema de nanoposicionamento do Fabry-Pérot, composto de sensores capacitivos, conversores de sinal, atuadores piezoelétricos e sistema de aquisição de dados. Após a caracterização dos componentes do sistema, sua especificação técnica de desempenho de 3 foi traduzida em requisitos de engenharia para o projeto do sistema eletrônico de acionamento dos piezos por carga e tensão, notadamente em termos de ruído, tempo de resposta, banda de resposta em frequência, ganho, corrente e tensão elétricas e dissipação de potência. Uma vez concluído o projeto do driver, um protótipo foi implementado e testado com o sistema real, a fim de se verificar experimentalmente a atenuação dos efeitos não lineares. Finalmente, foram realizados alguns experimentos com o driver e o sistema de nanoposicionamento em malha fechada, controlado por um compensador PI, a fim de se verificar a influência da atenuação das não linearidades dos piezos nesta configuração. Após a análise dos resultados experimentais obtidos, verificou-se que o ruído de posicionamento do sistema, em malha fechada, é significativamente menor quando os fenômenos não linearidades dos piezos são atenuados. / This work represents the research project to obtain the degree of Master of Sciences in Electrical Engineering, specializing in Systems Engineering, at the Escola Politécnica da Universidade de São Paulo, in São Paulo, Brazil. The main objective of this project was to design an electronic power driver for the piezoelectric actuators of the Fabry-Pérot interferometer of the BTFI spectrometer, a visitor instrument of the SOAR telescope, in Chile. Fabry-Pérot is an optical instrument composed by two high reflexive parallel surfaces (mirrors), which distance is controlled by a nanopositioning system composed by three piezoelectric actuators (piezos) of the class APA® (Amplified Piezoelectric Actuators) and a capacitive measurement system. The main performance specification of the Fabry-Pérots nanopositioning system is such that the positioning noise must be limited to 3 . However, the nonlinear behaviors (hysteresis and creep) of the piezos limit the positioning precision of the control system, for which reason a charge and voltage actuation system was developed for the piezos, in order to mitigate its nonlinearities and, consequently, improve the performance of the control system in closed loop, in terms of positioning noise. The first step in this work consisted on the characterization of the Fabry-Pérot nanopositioning systems model and instrumentation, which are composed by capacitive sensors, signal converters, piezoelectric actuators and a data acquisition board. After the characterization of the components of the nanopositioning system, the 3 specification was interpreted to low level engineering requirements for the design of the charge and voltage driver, especially in terms of noise, response time, frequency bandwidth, gain, electrical current, voltage and power dissipation. Once concluded the design of the driver, a prototype was implemented and tested in the real system, in order to verify the attenuation of the nonlinear effects. Finally, some experiments with the driver and the nanopositioning system were performed in closed loop, controlled by a PI compensator, in order to verify the influence of the attenuation of the nonlinearities of the piezos in such configuration. The analysis of the obtained experiment results showed that the nanopositioning systems noise, in closed loop, is significantly reduced when the nonlinear effects of the pizeos are attenuated.

Tato diplomová práce se zabývá technologií tlustých vrstev a jejím možným použitím pro nekonvenční aplikace. První část práce je rešeršní a zaměřuje se především na aplikace tlustovrstvé technologie v různých oblastech použití. V teoretické části práce je dále popsána technologie LTCC, včetně technologických postupů výroby. V praktické části jsou řešeny dvě aplikace v tlustovrstvé technologii. Jedná se návrh a výrobu vysokofrekvenčního filtru a optického senzoru tlaku technologií LTCC. V závěru práce jsou provedena měření a jsou zhodnoceny dosažené výsledky.

In der vorliegenden Promotion werden zwei ausgewählte Iridate mit Elektronen-Spin-Resonanz untersucht. Bei der ersten Probe handelt es sich um das Doppelperowskit Ba2YIrO6, das nach simpler theoretischer Auffassung kein paramagnetisches Signal besitzen sollte. Allerdings zeigen unterschiedliche magnetische Messungen schwache magnetische Spinkorrelationen. Mit Hilfe von ESR kann die Ursache dieser Signale paramagnetischen Verunreinigungen zugeschrieben werden. Zudem kann der Ursprung dieser Defekte mit zwei unterschiedlichen Oxidationsstufen des Iridiums assoziiert werden.    Bei der zweiten untersuchten Iridat-Probe La2CuIrO6 handelt es sich ebenfalls um ein Material mit Doppelperowskit-Struktur, allerdings interagieren hier zwei grundlegend verschiedene Spinsorten miteinander. Zum einen der sich aus der starken Spin-Bahn-Kopplung ergebende Jeff=1/2 Pseudospin des Iridats und zum anderen der reine S=1/2 Spin des Kupferions. Innerhalb der Kristallstruktur ergibt sich daraus eine komplexe antiferromagnetische Spinstruktur mit einer kleinen Verkippung der Spins. Diese nicht-kollineare Spinanordnung geht auf die Dzyaloshinskii-Moriya-Wechselwirkung zurück und führt letztendlich zu einem kleinen ferromagnetischen Nettomoment. Mit ESR konnte dabei vor allem die temperaturabhängige Wechselwirkung der einzelnen Untergitter gezielt untersucht werden. Zusätzlich zum experimentellen Teil war eine der Kernaufgaben dieser Arbeit die technische Realisierung eines Fabry-Perot Resonators. Ziel des Resonators ist dabei die Erhöhung des Signal/Rauschverhältnisses sowie die Implementierung die Probe innerhalb der Messapparatur zu rotieren. Um ein besseres Verständnis des zugrundeliegenden Resonanzverhaltens zu erhalten, wurden zudem einige Simulationen zum Verhalten der elektromagnetischen Wellen innerhalb des Resonators durchgeführt.

Ce travail de recherche a été mené afin d'introduire une nouvelle classe de résonateurs Fabry-Pérot (FP) : les cavités FP incurvées basées sur des miroirs de Bragg sans revêtement, de forme cylindrique sont obtenues par micro-usinage du silicium. Une autre spécificité est la longueur de la cavité relativement grande (L> 200 µm) combinée à un haut facteur de qualité Q (jusqu'à 10^4 ), pour répondre aux applications de type spectroscopie d'absorption améliorée par résonance optique, dans lesquelles le produit Q.L est une figure de mérite. Dans ce contexte, l'architecture de base a été modélisée analytiquement pour déterminer les modes transverses d'ordre élevé supportés par de telles cavités. Par conséquent, les conditions expérimentales qui conduisent à une excitation préférentielle (ou rejet) de ces modes ont été testées menant à la validation de notre modèle théorique et à une meilleure compréhension du comportement de la cavité. Une seconde architecture,basée sur la cavité FP incurvée avec une lentille cylindrique a été développée dans le but de fournir une architecture plus stable. Cette dernière a été également modélisée, fabriquée et caractérisée, menant à l'amélioration attendue en termes de performances. D'un autre côté, un point surlignant l'une des applications potentielles que nous avons identifiées pour les cavités incurvées est présentée en insérant la cavité dans un système électromécanique. Ceci consiste à exciter et mesurer les vibrations d'amplitude nanométrique par couplage opto-mécanique dans un résonateur mécanique MEMS intégrant une cavité optique FP. Enfin, comme complément à notre étude sur les résonateurs, nous avons commencé à explorer les applications des interféromètres optiques à base de miroirs de Bragg en silicium. À cette fin, un microsystème de mesure optique a été conçu, fabriqué et caractérisé, il consiste en une sonde optique pour la profilométrie de surface dans des milieux confinés, basé sur un interféromètre de Michelson monolithique en silicium / This research work has been conducted to introduce a novel class of Fabry-Perot (FP) resonators : curved FP cavity based on coating-free Bragg mirrors of cylindrical shape, obtained by silicon micromachining. Another specificity is the rather large cavity lengths (L>200 µm) combined with high quality factor Q (up to 104), for the purpose of applications requiring cavity enhanced absorption spectroscopy, in which the product Q.L is a figure of merit. In this contest, the basic architecture has been modeled analytically to know the high order transverse modes supported by such cavities. Hence, the experimental conditions which lead to preferential excitation (or rejection) of these modes have been tested experimentally leading to the validation of our theoretical model and to a better understanding of the cavity behaviour. A second architecture, based on the curved FP together with a fiber rod lens has been developed for the purpose of providing stable designs. It was also modeled, fabricated and characterized leading to the expected performance improvements. On another side, a highlight on one of the potential applications that we identified for the curved cavities is presented by inserting the cavity into an electro-mechanical system. It consists of exciting and measuring tiny vibration through opto-mechanical coupling in a MEMS mechanical resonator embedding an FP cavity.Finally, as a complement to our study on resonators, we started exploring applications of optical interferometers based on similar micromachined silicon Bragg mirrors. For this purpose, an optical measurement microsystem was designed, fabricated and characterized ; it consists of an optical probe for surface profilometry in confined environments, based on an all-silicon Michelson interferometer

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.

In the past decades, the miniaturization in optics led to new devices with structural sizes in the range of the light wavelength, where the photonic modes are con- fined and the number of states is limited. In the smallest microcavities, i.e. micrometer sized optical resonators, the propagation of only one mode is permitted that is simultaneously amplified internally. This particularly strong enhancement of the electric field is directly related to the quality factor of the cavity. By introducing an optical dipole into a high-Q microcavity, the spontaneous emission is amplified at the cavity mode frequency enabling stimulated emission in an inverted system. Although some of theses cavity e®ects can only be understood by quantum elec- trodynamic theory, most mechanisms are accessible by classical and semi-classical approaches. In this thesis, one-dimensional planar microcavities with quality factors up to 4500 have been fabricated by physical vapor deposition of dielectric thin films and organic active materials. A new cavity design based on anisotropic dielectric mirrors grown by oblique angle deposition microcavities with two energetically shifted orthogonally polarized modes is presented. The application of these anisotropic structures for terahertz di®erence signal generation is demonstrated in spectrally and time resolved transmission experiments, where optical beats with repetition rates in the terahertz range are observed. Optically pumped organic vertical cavity surface emitting lasers (VCSELs) have been realized by applying an organic solid state laser compound and high reflectance distributed Bragg reflectors. These lasers combine a very low laser threshold with small beam divergence and good stability. A transfer of the anisotropic design towards an organic VCSEL results in the generation of two perpendicularly polarized laser modes with a splitting adjustable by the fabrication conditions. The observation of an oscillation of two laser modes in a photomixing experiment proves a phase coupling mechanism. This demonstrates the potential of the anisotropic cavity design for a passive or active component in a terahertz radiation source or frequency generator. Furthermore, microcavities with two and three coupled resonators are investigated. By the application of time-resolved transmission experiments, spatial oscil- lations of the internal electric field - photonic Bloch oscillations - are successfully demonstrated. In combination with the anisotropic microcavities, this is a second concept for the modulation of transmitted light with terahertz frequencies. All experiments are accompanied by numerical or analytical models. Transmission experiments of continuously incident light and single laser pulses are compared with transfer matrix simulations and Fourier transform based approaches. For the modeling of emission experiments, a plane wave expansion method is successfully used. For the analysis of the organic VCSEL dynamics, we apply a set of rate equations that explains the gain switching process.

Title: Magnetic nanostructures for recording and optical sensors Author: Eva Lišková Department: Institute of Physics, Charles University Supervisor: Prof. Ing. Štefan Višňovský, DrSc. Abstract: Magneto-optical (MO) spectra of multilayered structures with enhanced MO effect were studied using the polar and longitudinal Kerr spectroscopy with oblique angle of light incidence in the photon energy range 1.2 eV to 5 eV. The samples with Fabry- Perot cavity like architecture, were modeled using Yeh matrix formalism. Two sets of samples, with composition FeF2/Fe/FeF2 and AlN/Fe/AlN, were prepared by molecular beam epitaxy and sputtering. The relations were studied between the position of the enhanced peak in the MO spectra and the structure. Second part of this work was devoted to the Pt/Co/Pt structures and the influence of the ion implantation on MO spectra and structural composition. The studied multilayer structures present interest for MO sensor and memory applications. Keywords: Magneto-optical Kerr effect, Magneto-optical sensor, Fabry-Perot resonator, Ion implantation

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.

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