Este trabalho trata do desenvolvimento de um sistema de controle para um módulo do instrumento astronômico BTFI (Brazilian Tunable Filter Imager), um filtro óptico sintonizável altamente versátil que está instalado no telescópio SOAR, localizado no Chile. Será empregado neste instrumento um novo interferômetro Fabry-Perot, capaz de realizar observações em uma ampla faixa de resoluções espectrais. Para operar com resolução espectral variável, o Fabry-Perot proposto neste projeto terá uma faixa mais ampla de ajuste do vão entre suas placas refletivas, utilizando atuadores piezelétricos amplificados com grande capacidade de deslocamento e sensores capacitivos de alta precisão. O novo controlador apresenta uma malha de controle totalmente digital, implementada com um DSP (Digital Signal Processor) sintetizado num dispositivo FPGA (Field-programmable Gate Array). Na primeira etapa do desenvolvimento, trabalhou-se com um sistema de posicionamento nanométrico utilizando um protótipo simplificado com um canal composto por um sensor capacitivo de distância e um atuador piezelétrico. A partir dos bons resultados obtidos no sistema de um canal, realizou-se a expansão para um sistema de controle multi-malha de três canais com protótipo do Fabry-Perot, mas sem o uso das placas de vidro refletivas definitivas. O sistema permite controlar o posicionamento para cada canal individualmente ou os três em simultâneo, com desempenho adequado para os requisitos do filtro óptico sintonizável Fabry-Perot. / This work aims the development of a control system for a module of the BTFI astronomical instrument (Brazilian Tunable Filter Imager), a highly versatile optical tunable filter, deployed on the SOAR Telescope. The instrument will employ a new Fabry-Perot interferometer, which is able to provide observations in a wide range of spectral resolutions. In order to achieve variable spectral resolution, the new Fabry- Perot proposed in this project will present a larger range for adjusting the air gap between its reflective plates, using amplified piezoelectric actuators presenting high stroke capability and high precision capacitive sensors. The new controller presents a full digital control loop, implemented in a DSP (Digital Signal Processor) synthesized through a FPGA device (Field-programmable Gate Array). During the first phase of the development, it was used a nanometric positioning system using a single channel prototype comprising one capacitive sensor and one piezoelectric actuator. The good results obtained using the single channel prototype led to the expansion to a 3- channel multi-loop control system on a Fabry-Perot prototype which comprises dummy plates. The system allows controlling the position of each channel separately or simultaneously, presenting performance in accordance with the requirements of a Fabry-Perot optical tunable filter.

Cette thèse a pour but de mettre en avant les récentes avancées dans le domaine des métasurfaces. Ces structures ont été utilisées dans le but d’améliorer les performances des antennes classiques ou de concevoir de nouveaux concepts d’antenne. Les travaux menés s’inscrivent dans le cadre d’une collaboration avec des partenaires industriels qui sont Airbus Safran Lunchers, Airbus Group Innovations et le CNES. La thèse est organisée en deux parties. La première partie est consacrée aux métasurfaces utilisées comme des surfaces partiellement réfléchissantes (SPR) pour concevoir des antennes à cavité Fabry-Perot. Un modèle analytique permettant de prédire le dépointage du faisceau d’antenne par une modulation de la phase sur la SPR a été développé. Ensuite, un nouveau concept de métasurface permettant de réaliser du dépointage de faisceau est proposé. Il consiste à appliquer un gradient de phase en faisant varier l’indice effectif le long du substrat diélectrique de la SPR. La deuxième partie de cette thèse est quant à elle consacrée à la conception d’une métasurface active permettant d’émuler plusieurs fonctions. Dans un premier temps, la métasurface est utilisée comme un réflecteur présentant une reconfigurabilité fréquentielle et angulaire. Ensuite cette métasurface est utilisée comme polariseur reconfigurable où une polarisation linéaire de l'onde incidente est convertie en polarisation circulaire. Enfin, la dernière étude concerne l’utilisation de la métasurface active pour la réalisation d’une antenne à réflecteur cylindro-parabolique et à réflecteur dièdre reconfigurables. / This thesis aims at highlighting recent advances in the field of metasurfaces. These structures have been used to improve the performances of conventional antennas or to design new antenna concepts. The work has been carried in the framework of a collaboration with industrial partners, namely Airbus Safran Launchers, Airbus Group Innovations and CNES. The manuscript is organized into two parts. The first part is devoted to metasurfaces used as partially reflecting surfaces (PRS) to design Fabry-Perot cavity antennas. In this part, an analytical model allowing to predict the beam steering angle by a phase modulation along the PRS is developed. Then, a new concept of metasurface allowing to steer the main antenna beam is proposed. It consists in applying a phase gradient by varying the effective index of the substrate that constitutes the PRS. The second part of this thesis is devoted to the design of an active metasurface that allows emulating different functionalities. First, the metasurface is utilized as a reflector with frequency and steering reconfigurability characteristics. Then, this metasurface is used as a reconfigurable polarizer where linearly polarized incident waves are converted into circularly polarized ones. Finally, the last study concerns the use of the active metasurface for the design of reconfigurablecylindro-parabolic and corner reflector antennas.

Since the discovery of optical bistability a considerable amount of research activity has been aimed toward the realization of general-purpose all-optical computers. The basic premise for most of this work is the widely held notion that a reliable optical switch can be fabricated from a piece of optically bistable material. To date only a very small number of published articles have addressed the subject of the engineering issues (that is, the optimization and tolerancing) of these optical switches. This dissertation is a systematic treatment of these issues. From the starting point of Maxwell's equations a simple model of optically bistable Fabry-Perot etalons is outlined, in which the material is assumed to be a pure Kerr medium having linear absorption. This model allows for a relatively straightforward optical switch optimization procedure. The procedure is applicable for optimizing any number of switch parameters. The emphasis in this dissertation is on the optimization of the contrast of the switch's output signals, with the other parameters (switching energy, tolerance sensitivity) assuming a secondary yet critical role. Following the optimization of the optical switch is a tolerance analysis which addresses the manufacturability and noise immunity of the optimized switch. In the first part of this analysis equations describing the propagation of errors through a large scale system of like devices are derived from the truth tables of the switches themselves. From these equations worst case tolerances are established on the optical switch's transfer function parameters. In the second part of the tolerance analysis the bistability model is used to arrive at tolerances on the physical parameters of the switch. These tolerances are what determine the manufacturability of the optical switches. The major conclusion of the dissertation is that, within the range of validity of the model and the other simplifying assumptions, optically bistable Fabry-Perot etalons cannot be used reliably as logic gates in large-scale computing systems.

Accurate, spatially resolved wind measurements in the lower atmosphere are critical to improving current weather forecasting models. Wind shear detection for midsized airports, not covered under the Federal Aviation Administration's (FAA's) Terminal Doppler Weather Radars, would significantly reduce personal aircraft accidents. Atmospheric dynamics studies would also benefit from high accuracy, spatially resolved wind profiles within the planetary boundary layer.This dissertation discusses a thorough investigation of a novel alternating frequency incoherent Doppler lidar method named, the Alternating Edge Technique. After discussing the necessary background, a theoretical development of how the Alternating Edge Technique can be used to estimate the molecular to aerosol backscatter ratio is presented. The ability to estimate the molecular component vastly improves the accuracy of wind measurements, and adds additional information about the atmosphere being probed. A detailed modeling program was developed to evaluate the expected performance of this instrument, and to allow comparisons to be made of various components and operating conditions. Several of the key components are then evaluated experimentally, and these results are used to perform realistic Monte Carlo simulations in order to evaluate the ability of the Alternating edge technique, using available components, to estimate the molecular component of the backscattered light, and to accurately estimate average wind speed.

[Truncated abstract] This study investigates the mechanical and physical properties of low-temperature (100-300 ?C) plasma enhanced chemical vapour deposited (PECVD) silicon nitride (SiNxHy) thin films for the fabrication of short-wave infrared tunable Fabry-Perot filters with high fill factor, high cavity finesse and low actuation voltages. It has been the intensions of this work to fabricate a tunable filter that can be monolithically integrated with temperature-sensitive substrates, namely mercury cadmium telluride (Hg(1-x)CdxTe) photoconductors and photodiodes. A range of methods have been utilised to determine the Young's modulus (E), residual stress ([sigma]0), density ([rho]) and Poisson's ratio ([nu]) of PECVD SiNxHy thin films. In order to understand how E, [sigma]0, [rho] and [nu] are affected by process conditions, a range of SiNxHy thin films deposited with varying chuck temperatures, RF powers and chamber pressures were measured. The resonance method was used to determine E and [nu] of SiNxHy thin films deposited under varying process conditions. The resonance method involves exciting the bending and torsional vibration modes of a microcantilever beam fabricated from a film. The E and G values can be extracted directly from the bending and torsional vibration modes and the [nu] value can be determined from the calculated E and G values. The density of the films was determined using the quartz crystal microbalance method. In order to determine the validity of the resonance method, finite element modelling was used to determine its dependence on microcantilever beam dimensions. ... Increasing the temperature also increases the tensile residual stress of the films. This study also reveals that increasing the RF power and decreasing the chamber pressure increases E and [rho], as well as increasing the compressive residual stress of the films. The theoretical design and analysis, as well as the fabrication of a new surface micromachined short-wave infrared tunable Fabry-Perot filter for adaptive infrared photon detectors is also presented in this study. The proposed structure, termed the suspension filter, uses broad spectral range, high reflectivity distributed Bragg reflector (DBR) mirrors, resulting in very high finesse filters. The device utilises multiple sacrificial layers to define the resonant cavity spacer and the separation of the top mirror from the supporting flexures. The flexures were fabricated from low-temperature (PECVD) SiNxHy thin films. Separation of the top mirror from the supporting flexures allows for improved fill-factors (up to 79%), as well as increased tuning range. Theoretical optical and electromechanical results shows large wavelength tuning ranges (1.5-2.5 [mu]m) at low actuation voltages (<30 V) are possible using the proposed design, whilst still maintaining a high cavity finesse. Optical characterisation of fixed filter micro-cavities on Si substrates show transmissions of ~60% with small line widths (35 nm) are achievable using the proposed mirror system. Mirror displacement versus applied bias voltage curves obtained from a released filter fabricated on Si show a stable mirror displacement of 620 nm was achieved, whilst theoretical results suggested the required 750 nm mirror displacement is possible using the proposed design.

In this study, we fabricated an electrically wavelength-tunable resonant-cavity light emitting diode (RCLED). It was achieved by the combination of an AlGaInAs quantum well structure with an intra-cavity liquid crystal material. In the phase modulator layer, we used nematic liquid crystal (NLC) and cholesteric liquid crystal (CLC), respectively, comparing their difference in the infrared-spectrum. When inserting NLC, the anisotropic properties of liquid crystal enable continuous tuning of mode emission along the extraordinary direction and provide a 58 nm tuning range. The optical characteristics of this device are polarization dependent. On the contrary, the CLC-based device is polarization independent because any polarization of incident light experiences the same averaged refractive index. However, the phase difference of CLC is less than NLC, only a 41 nm tuning range of this sample. We also simulated and discussed experimental results of NLC-based RCLED. The optical pumping of the active region is realized by a CW laser at 1064 nm wavelength and observed at room temperature.

All-fiber multireflector spectral filters which have potential application in optical communications have been investigated experimentally. These multireflector etalons were produced by aligning equal-length fiber sections with TiO2/SiO2 dielectric mirrors deposited on the end in a silicon v-groove. Fiber sections 1.33mm in length were produced by polishing, with the fibers held in a silicon wafer polishing jig. The fibers were aligned inside the polishing jig using a precision micro positioner. Then four polishing steps with increasingly finer grit were applied to produce high-quality polished end surfaces on each fiber section. Finally, a dielectric mirror was deposited on one end of each fiber section by magnetron sputtering. After characterizing the optical loss, length, and mirror reflectance for each of the fiber sections, sections which were well-matched in length were chosen for assembly of the four-mirror etalon, which had nominal reflectance values of 10%, 50%, 50%, and 10% for the dielectric mirrors. Measured transmittance spectra for a mutireflector spectral filter were compared with calculated spectra. Thermal tuning of the multireflector etalon was also investigated. A 0.34 nm wavelength shift was observed for a 23° C temperature change, in agreement with prediction. increasingly finer grit were applied to produce high-quality polished end surfaces on each fiber section. Finally, a dielectric mirror was deposited on one end of each fiber section by magnetron sputtering. After characterizing the optical loss, length, and mirror reflectance for each of the fiber sections, sections which were well-matched in length were chosen for assembly of the four-mirror etalon, which had nominal reflectance values of 10%, 50%, 50%, and 10% for the dielectric mirrors. Measured transmittance spectra for a mutireflector spectral filter were compared with calculated spectra. Thermal tuning of the multireflector etalon was also investigated. A 0.34 nm wavelength shift was observed for a 23° C temperature change, in agreement with prediction.

Thesis (Ph. D.)--University of Adelaide, Mawson Institute, 1989. / Includes bibliographical references (leaves 140-151).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 78-80). Also available via the Internet.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 86-87). Also available via the Internet.