Polímeros contendo grupos azo-benzênicos têm sido estudados devido a sua capacidade para óptica não linear, formação de superfícies de relevo e de birrefringência fotoinduzida. O fator que possibilita essas aplicações é a propriedade de fotoisomerização reversível trans-cis-trans do grupo azo que produz a sua reorientação molecular. Neste trabalho foram produzidos filmes casting do poliuretano MDI-DR19 derivado de azo-benzeno. Estudou-se o crescimento e decaimento da birrefringência para diferentes valores de potência da luz de excitação da fotoisomerização. Os resultados experimentais do crescimento e decaimento foram analisados usando duas exponenciais e eles mostraram que o polímero MDI-DR19 apresenta boas características para utilização em armazenamento óptico pois cerca de 65% da birrefringência induzida no material permanece por longos intervalos de tempo. Ilustramos o processo de armazenamento de informação gravando uma imagem de birrefringência num filme de MDI-DR19. Foram também produzidas grades de relevo em filmes de MDI-DR19 utilizando franjas de interferência produzidas com luz de polarização P e S. Essas grades apresentaram alta uniformidade e características compatíveis com as mostradas na literatura. / Polymers containing azobenzenic groups have been studied due to their applications on non-linear optics, surface relief gratings (SRG) and photoinduced anisotropy for optical storage. The reversal photoisomerization trans-cis-trans property of the azo group induces a molecular reorientation. In this work, cast films of na azobenzene derivative, the polyurethane MDI-DR19, were studied. The build-up and decay of the birefringence were studied as a function of the photoisomerization exciting light power. The data of the build-up and decay of the birefringence were fitted with a bi-exponential function, which shows the stability of the MDI-DR19 for application in optical storage, since 65% of the induced birefringence remains after a long time. The optical storage is illustrated by recording a birefringence image in a film of MDI-DR19. It was also performed a SRG over films of MDI-DR19 applying an interference finger pattern with a P and S polarized light. The light induced gratings shows good uniformity and characteristics compatible with those presented in the literature.

Orientadores: Hugo Enrique Hernandez Figueroa , Júlio César Rodrigues Fernandes de Oliveira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-26T03:17:30Z (GMT). No. of bitstreams: 1 Freitas_AlexandrePassos_M.pdf: 2935936 bytes, checksum: 2bf660b1a9d7a183bc552d3db9da1b97 (MD5) Previous issue date: 2014 / Resumo: O crescente aumento da demanda de tráfego de dados dos sistemas de comunicação ópticos em conjunto com a busca da integração e miniaturização cada vez maior dos componentes impulsionaram a fotônica integrada em silício como uma das tecnologias promissoras para a evolução das novas gerações de dispositivos ópticos. Esta tecnologia, além de possuir suas características de um alto contraste de índice de refração, capacidade de modulação óptica através de controle de temperatura ou por densidade de portadores, se utiliza da infra-estrutura de fabricação para a indústria de microeletrônica já desenvolvida nas últimas décadas. Neste cenário, este trabalho propõe o desenvolvimento de um modulador de fase fabricado com a tecnologia de fotônica integrada em silício para o formato de modulação DP-QPSK e que opere na banda C de comunicação óptica. Análises de simulações e experimentais foram realizadas para a validação do fluxo de desenvolvimento do circuito e de cada componentes utilizado individualmente / Abstract: The increasing demand for data in optical communication systems with a constant search for reduction of device dimensions boosted silicon photonics as a candidate technology to the following optical device generations. Besides having high refractive index contrast, modulation capabilities through thermal or by carrier density control, this technology takes advantage of the microelectronic infra-structure developed in the last decades to fabricate small optical components with high reliability. In this scenario, this dissertation proposes the design of a phase modulator in silicon photonic technology. This modulator is able to operate at C-band and make the DP-QPSK modulation. Simulation and experiment analysis were made to validate the design flow for the optical circuit and for each single component / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

SALT HRS (Southern African Large Telescope High Resolution Échelle Spectrograph) is a high-resolution, high-efficiency spectrograph for the 11m SALT telescope in Sutherland, South Africa. The initial optical design work was performed at the University of Canterbury, New Zealand. Revisions to the concept, the mechanical design, manufacture, assembly and testing have been handled by the Centre for Advanced Instrumentation, at Durham University in the United Kingdom. SALT HRS is a fibre-fed echelle grating spectrograph with four operational modes: low-, medium- and high-resolution and high-stability modes, having spectral resolutions of R ≈16000, 37000, 67000 and 67000 respectively over a wavelength range of 370-890nm. The instrument is of a dual channel, ‘white pupil’ design, in which the primary mirror acts to collimate light onto a single R4 echelle grating, and also to focus dispersed light to an intermediate focus. A dichroic beam-splitter separates the dispersed light into two separate spectral channels. Spherical pupil mirrors transfer the separated beams via a fold mirror to two wavelength-specific volume-phase holographic gratings (VPHGs) used as cross-dispersers. Cross-dispersed spectra are then imaged by two fully dioptric camera systems onto optimized CCD detectors. This thesis presents the results of the laboratory testing and specification of several critical sub-systems of SALT HRS, as well as the development of key software tools for the design verification and operation at the telescope. In Chapter 1 we first review the technical development of high-resolution spectroscopy and its specific implementation in SALT HRS. In Chapter 2 we develop a comprehensive throughput model of the entire system based on a combination of as-built performance and specific throughput measurements in the laboratory. This is used to make some specific predictions for the on-sky performance of SALT HRS and the magnitude limits for science targets. We also present a graphical exposure time calculator based on these measurements which can be used by an astronomer to plan their observations with SALT HRS. Chapter 3 contains a detailed treatise on the optical fibre system of SALT HRS. Considerations for the use of optical fibres in astronomy are provided, as are details of an optional double scrambler, and the various instrument fibre modes. Extensive measurements of focal ratio degradation (FRD) are also presented, with testing of input beam speed; wavelength; fibre bending; variable pupil mirror illumination; and vacuum tank pressure dependency. The systems for fibre management are reviewed, as is the fibre bundle assembly process. Testing of two further sub-systems is described in Chapter 4. Firstly the long-term stability of the mirror mounting mechanisms is determined. The advantages of cross-dispersion of echelle spectra using volume-phase holographic gratings are then discussed, and the results of diffraction efficiency measurements are given for both red and blue channel gratings. Modern CCD technologies are examined in Chapter 5, and the blue detector is experimentally characterized using photon transfer and quantum efficiency curves. It is also used for an investigation into cosmic ray events in CCDs. Results from shielding the detector using lead are described, as is an attempt to distinguish the source of the events based on their morphology. Finally, Chapter 6 deals with the handling of data produced by SALT HRS. Methods of wavelength calibration of the spectra are discussed, including the use of Thorium-Argon lamps and an iodine absorption cell. The implementation of a Python based quick-look data reduction pipeline is reviewed, with a description of the processes performed. A summary of the thesis is given in Chapter 7.

Sensors have become essential elements in human life for safe and comfortable existence in the ever demanding world. Various technologies over decades have contributed in their own way fulfilling innumerable sensing requirements. The discovery of optical sensor technologies has revolutionized the sensing field due to their inherent advantages. Among the large number of fiber optic sensor technologies, FBG based sensors have become widely known and popular within and outside the photonics community and has seen a prominent rise in their utilization. This thesis explores the use of FBG sensors for a wide range of applications scanning across a variety of engineering and medical applications, in the areas of civil engineering, biomechanical engineering, aerospace engineering, geoengineering, etc. It also deals with newer methods of packaging FBG sensors for the measurement of specific engineering parameters like strain, temperature, pressure, displacement and vibration. In the field of civil engineering, FBG sensors are employed for strain sensing on a prism and furthermore tested on a full size brick wallet. During this study, emphasis is made on substituting traditional sensors by specially packaged FBG sensors with the intent of either enhancing the sensing system’s performance or in merging/uniting the inherent advantages of FBG sensors. In the area of biomechanics, a novel sensor methodology using FBG sensors, for measuring surface strains generated on the skin of the calf muscle during various leg exercises is proposed. This methodology is used to address one of the most critical and life threatening issues in long distance air travel, namely the Deep Vein Thrombosis. Further, a FBG sensor based plantar sensing plate, is designed and developed, to measure plantar strain distribution in foot and also to analyze the postural stability. In the field of aerospace engineering, FBG sensors are used for addressing two of the most vital issues; Structural Health Monitoring (SHM) and direct measurement of pressure and temperature on the surface of an aircraft under hypersonic wind flow. Carbon Fiber Composite coupon level testing is carried out to obtain a generic strain calibration factor for the FBG sensor. Further, FBG sensors are exploited for the direct measurement of absolute temperature and pressure on the leeward surface of blunt cone at hypersonic wind speeds. In the domain of geoengineering, the feasibility studies have been undertaken to use a FBG as a seismic sensor and as a bore-well characterizing sensor. A novel FBG seismic sensor package is developed using a single FBG sensor to pick up the seismic waves propagating through the ground generated from earthquakes and ground tremors. Further, FBG sensors are used for measurement of temperature profiles in a bore-well to delineate and characterize the behavior of fractures during seasonal climatic changes. To summarize, the present thesis demonstrates a comprehensive experimental study which bring out the utility of FBG sensors in a variety of challenging applications.

[pt] Linhas de transmissão de energia são estruturas importantes em um sistema de energia elétrica. Devido à elevada energia transportada por essas redes, falhas em linhas de transmissão podem ter reflexos severos no fornecimento aos consumidores, não raro levando a apagões em áreas geograficamente extensas. Entre as possíveis origens de falhas está o rompimento dos cabos elétricos pela fadiga provocada pela vibração eólica. As grandes extensões territoriais percorridas pelas linhas de transmissão e a variedade de climas, relevos, vegetação e condições meteorológicas aos quais estão submetidas dificultam qualquer trabalho de previsão da ação do vento. A medição da vibração permite detectar de antemão a aproximação da falha, porém os instrumentos convencionais dependem de transdutores elétricos os quais, além de exigirem uma fonte de energia (normalmente não disponível junto a linhas de transmissão) para seu funcionamento, sofrem influência dos intensos campos elétricos e magnéticos existentes em torno dos cabos de energia. A imunidade das fibras ópticas a campos elétricos e magnéticos e a possibilidade de uso de sinal de entrada de baixa potência oferecem uma alternativa para a criação de instrumentos de medição usando a técnica das redes de Bragg. A presente dissertação contribui com o desenvolvimento de um acelerômetro biaxial a redes de Bragg para medição de vibração em cabos de linhas de transmissão de energia. Além dos aspectos teóricos e práticos envolvidos, são discutidos os resultados de ensaios de calibração de elevada exatidão e outros ensaios especiais que fundamentaram a avaliação metrológica e o estabelecemento da eficácia do referido instrumento. / [en] Overhead transmission lines play an important role on electric systems. Due to the high energy carried through those networks, failures on overhead lines can bring severe constraints on consumers supply, occasionally taking the form of blackouts in large geographic regions. Among the reasons of such failures is the breaking of electric cables caused by the fatigue originated from cyclic bending due to aeolian vibration. The large areas covered by overhead lines and the variety of climate, relief, vegetation and meteorological conditions under which they have to operate make it difficult to foresee the impact of wind Vibration measurements would allow anticipating the failure but conventional instruments depend upon electric transducers which, besides demanding a local source of energy (usually unavailable near overhead lines), suffer the influence of the high electric and magnetic fields around the energized cables. Optical fibers immunity against environments subjected to electrical and magnetic fields and the possibility of using low energy input signals offer the alternative of creating measuring instruments using Bragg gratings technique. This Master dissertation contributes with the development of a fiber Bragg grating biaxial accelerometer for measuring the vibration of overhead transmission line cables. Besides the theoretical and practical aspects related to the subject, the results of high precision calibration tests are discussed, together with other special tests which set the basis of the metrological evaluation and the establishment of the efficacy of the instrument.

In my research work, I study diffraction by planar periodic structures (diffraction grating). In the first chapter, I try to familiarize the importance of diffraction gratings in spectroscopy. The second chapter explains the basic principle of diffraction without involving difficult mathematical tools. In the third chapter, I deduce Fourier modal method from Maxwell equations, a modern mathematical approach used for calculating the electromagnetic response of diffraction. The most important part of my work consists of the fourth and fifth chapter. At first, I try to utilize Fourier modal method for deriving formulas involving just 0th and (-1)st diffraction orders. Because of the unreasonable difficulty of uncovered formulas, I decided to consider only a special case - so-called Littrow configuration, in which the solution can be superposed from symmetric and antisymmetric couples of rays. I further develop so-called Local modal method - very inaccurate, but mathematically fairly simple, and discuss its physical limitations. Whole work is finished by the sixth chapter, which compares accurate computations gained from simulation and derived analytical formulas for both methods.

Title: Surface plasmons in optical microstructures and their sensor applications Author: Pavel Adam Institute: Institute of Photonics and Electronics AS CR, v.v.i., Department of Optical Sensors Supervisor of the doctoral thesis: doc. Ing. Jiří Homola, CSc., DSc. Abstract: This work is focused on the study of surface plasmon resonance (SPR) sensor platforms based on wavelength division multiplexing (WDM) of multiple surface plasmons (SPs). These sensors are based on advanced diffraction gratings supporting either conventional or Bragg-scattered SPs, which are simultaneously excited at different wavelengths. These SPs are studied both analytically and numerically using rigorous coupled-wave analysis and an integral approach. WDM of two and three SPs is presented and followed by the method for the analysis of the resolution, noise and cross-sensitivity. This method is employed to analyze the ability of different SPR sensor platforms (supporting WDM of two SPs) to discriminate refractive index (RI) changes in a thin layer at the sensor surface from background RI changes. The WDM SPR sensors based on advanced diffraction gratings prepared by interferometric holography are developed and tested in a model biosensing experiment consisting of the layer-by-layer growth of protein multilayers. The linear WDM of two...

This dissertation presents the fabrication and analysis of in-fiber devices based on elliptical core D-shaped optical fiber. Devices created inside optical fibers are attractive for a variety of reasons including low loss, high efficiency, self-alignment, light weight, multiplexibility, and resistance to electromagnetic interference. This work details how D-fiber can be used as a platform for a variety of devices and describes the creation and performance of two of these devices: an in-fiber polymer waveguide and a surface relief fiber Bragg grating. In D-fiber the core is very close to the flat side of the ‘D’ shape. This proximity allows access to the fields in the fiber core by removal of the cladding above the core. The D-fiber we use also has an elliptical core, allowing for the creation of polarimetric devices. This work describes two different etch processes using hydrofluoric acid (HF) to remove the fiber cladding and core. For the creation of devices in the fiber core, the core is partially removed and replaced with another material possessing the required optical properties. For devices which interact with the evanescent field, cladding removal is terminated before acid breaches the core. Etching fibers prepares them for use in the creation of in-fiber devices. Materials are placed into the groove left when the core of a fiber is partially removed to form a hybrid waveguide in which light is guided by both the leftover core and the inserted material. These in-fiber polymer waveguides have insertion loss less than 2 dB and can potentially be the basis for a number of electro-optic devices or sensors. A polarimetric temperature sensor demonstrates the feasibility of the core replacement method. This work also describes the creation of a surface relief fiber Bragg gratings (SR-FBGs) in the cladding above the core of the fiber. Because it is etched into the surface topography of the fiber, a SR-FBG can operate at much higher temperatures than a standard FBG, up to at least 1100 degrees Celsius. The performance of a SR-FBG is demonstrated in temperature sensing at high temperatures, and as a strain sensor.

Light detection and ranging (lidar) is used for various applications such as remote sensing, altimetry and imaging. In this talk, a linearly chirped pulse source is introduced that generates wavelength-swept pulses exhibiting ~6 nm optical bandwidth with > 20 km coherence length. The chirped pulses are used in an interferometric lidar setup to perform distance measurements with sub-millimeter resolution (using pulses that are a few meters long), at target distances > 10 km, with at least 25 dB signal-to-noise ratio at the receiver. A pulse repetition rate of 20 MHz provides fast update rates, while chirped pulse amplification allows easy amplification of optical signals to high power levels that are required for long range operation. A pulse tagging scheme based on phase modulation is used to demonstrate unambiguous, long range measurements. In addition to this, simultaneous measurement of target range and Doppler velocity is performed using a target moving at a speed of over 330 km/h (205 mph) inside the laboratory. In addition to this, spectral phase modulation of the chirped pulses is demonstrated to compensate for the undesirable ripple in the group delay of the chirped pulses. Moreover, spectral amplitude modulation is used to generate pulses with Gaussian temporal intensity profiles and a two-fold increase in the lidar range resolution (284 um) is observed.

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