Photovoltaics (PV) are a renewable energy technology experiencing rapidly increasing commercial adoption today. Nonetheless, many proposed PV applications still require higher efficiencies, lower costs and comparable reliability to currently available in commercial devices (typically made from silicon). To enable the rigorous study of a much wider range of materials and novel design concepts, particularly those based on compound thin films, Concentrated Photovoltaics (CPV), cells with bifaciality, a comprehensive modeling framework is developed to couple photon absorption, carrier transport, photon recycling, and thermal transport in PV devices. The universality of this framework manifest itself in approaching various PV related problems as follows: 1) exploring the novel design of wide-Eg GaInP solar cells as an intermediate step to enhance the efficiency of multijunction PV devices; 2) characterizing the open-circuit voltage (VOC) degradation in thin-film vapor liquid solid (TF-VLS) grown InP solar cell through combined device and circuit model for interpreting photoluminescence (PL) image; 3) establishing optic-electric-thermal coupled framework to assess and compare the passive cooling effect for Silicon CPV devices that employ porous soda-lime glass radiative cooler and conventional copper cooler respectively; 4) Investigating and formulating the analytic solution of the optimal design that minimizes combined optical shadowing loss and electrical resistive loss for two types of bifacial PV devices: a) interdigitated back contact (IBC) Silicon heterojunction (SHJ) solar cells and b) Copper Indium Gallium DiSelenide (CIGSe) solar cell with Al2O3 passivation; and 5) Constructing an Neural Network Autoen- coder (NNA) that compresses and reconstructs the J-V characteristics obtained from TCAD simulation and literature for rapid screening and automated classification.

[pt] O presente trabalho tem como objetivo a realização de um transmissor experimental para comunicações ópticas baseado na modulação por chaveamento de polarização da luz, conhecida como Polarization Shift Keying (PolSK). Realizamos análise teórica das vantagens e desvantagens da modulação PolSK frente aos requisitos de desempenho das comunicações ópticas atuais, entre os quais a eficiência espectral, o consumo de energia e roteamento totalmente óptico em redes transparentes. A principal abordagem da dissertação está relacionada ao ganho em eficiência espectral que pode ser alcançado com o uso de constelações de símbolos num espaço dimensional denominado espaço de Stokes. Dados obtidos de um transmissor experimental de baixa velocidade demonstram a geração de constelações de símbolos tridimensionais contendo oito símbolos numa geometria de hexaedro (cubo). Com base nos conceitos teóricos, o arranjo experimental que construímos pode ser reproduzido para funcionar em velocidades compatíveis com as taxas de transmissão das comunicações ópticas atuais. / [en] The present work aims the experimental realization of an optical transmitter based on the Polarization Shift Keying modulation - known as (PolSK). We analyze theoretically both, advantages and disadvantages of PolSK modulation, emergent performance requirements for current optical communications systems, including spectral efficiency, power consumption and routing in the context of transparent all-optical networks. The main approach of the dissertation is related to the spectral efficiency gain that can be achieved when we use constellations of symbols in a dimensional space called Stokes space. Data from a low speed experimental transmitter demonstrate the generation of three-dimensional constellations of symbols containing eight symbols on hexahedron (cube) geometry. Based on the theoretical concepts we built the experiment, the setup can be replicated to operate at speeds compatible with transmission rates of current optical communications systems.

[pt] Diante do crescimento do interesse pelos amplificadores Raman faz-se necessário um estudo mais detalhado destes. Uma técnica tradicionalmente já utilizada para analise de atenuação em enlaces, a reflectometria óptica no domínio do tempo, é empregada de maneira inovadora neste trabalho para a observação da amplificação Raman distribuída. O objetivo principal deste trabalho não é a analise de amplificadores Raman, mas sim a apresentação desta técnica como nova ferramenta observação do ganho Raman distribuído em fibras ópticas. / [en] Due to increased interest in Raman amplifiers, a more detailed study of them is required. A technique traditionally used for analysis of attenuation on optical links, time domain optical reflectometry, is used in an innovative way in this work for observation of distributed Raman amplification. The main objective of this work in not the analysis of Raman amplifiers, but the introduction of this technique as a new tool for the observation of distributed Raman gain in optical fibers.

Data centre networks are currently experiencing a dramatic increase in the amount of network traffic that needs to be handled due to cloud technology and several emerging applications. To address this challenge, mega data centres are required with hundreds of thousands of servers interconnected with high bandwidth interconnects. Current data centre networks, based on electronic packet switches, consume a huge amount of power to support the increased bandwidth required by the emerging applications. Optical interconnects have gained more and more attentions as a promising solution offering high capacity and consuming much lower energy compared to the commodity switch based solutions. This thesis provides a thorough literature study on optical interconnects for data centre networks that are expected to efficiently handle the future traffic. Two major types of optical interconnects have been reviewed. One is referred to hybrid switching, where optical switching deals big flows while electronic switches handles traffic in packet level. The other one is based on all-optical switch, where power-consuming electronic interconnects can be completely avoided. Furthermore, the thesis includes a qualitative comparison of the presented schemes based on their main features such as topology, technology, network performance, scalability, energy consumption, etc.

<div>The Internet-of-Things (IoT) devices have experienced an explosive growth during the last decades. The number of IoT devices is predicted to reach 36.4 billion by 2025, resulting in an urgent demand for high-density and high-capacity network connectivity. Recently, self-powered optical wireless devices have attracted more attention from both academia and industry. Although radio frequency (RF) technologies are readily available for various wireless applications, the RF</div><div>communication bands are becoming saturated due to the scarcity of the RF spectrum. Optical wireless communication (OWC) provides an attractive solution to overcome the shortage of RF bands. OWC is also attractive for low-power or even self-powered applications since optical energy is the most abundant in both indoor and outdoor scenarios.</div><div><br></div><div>This dissertation explores a new optical communication technique called optical frequency identification (OFID). This technique employs solar cells as an optical antenna, capable of harvesting energy and transmitting/receiving optical information. Transmission of information with a solar cell is achieved by modulating the cell's luminescent emissions. Two OFID system prototypes were designed,</div><div>fabricated, evaluated, and discussed.</div><div><br></div><div>A series of experiments have been carried out to exploit the feasibility of using a solar cell's luminescence emissions for optical communication and evaluate proposed two OFID system prototypes. This dissertation validated that luminescent emissions from a GaAs solar cell can be modulated for optical communications. Then, two photoluminescence (PL) modulators were proposed and compared in terms of their energy harvesting and communication performances. The first OFID system prototype, based on a dual-aperture reader and a microcontroller-based tag was validated and experimented for a remote temperature sensing application. The second prototype, based on a single-aperture OFID reader and an FPGA-based OFID module, was analyzed with an emphasis on the communication date rate, communication range, tag's cold-startup period and power consumption.</div>

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[pt] Um estudo completo da dispersão dos modos de polarização (PMD) em fibras ópticas foi apresentado. Uma nova proposição de Emuladores de PMD com comprimentos de acoplamento aleatóriamente gerados foram comparados, teórica e experimentalmente, com os comumente encontrados na literatura. Um novo método para a medida da freqüência óptica em função do tempo baseado na técnica da discriminação de freqüências ópticas através de um filtro foi apresentado, mostrando suas vantagens sobre outro método encontrado na literatura. Utilizando este novo método foram medidas as características espectrais de alguns lasers DFB modulados em alta freqüência. Os efeitos das PMDs de primeira e segunda ordem em transmissões digitais de alta capacidade foram avaliados, através de medidas da distorção temporal do pulso óptico, bem como pelas penalidades de potência induzidas. O tratamento estatístico das penalidades de potência foi discutido, mostrando que as distorções por PMD de segunda ordem podem levar a uma eventual melhora do desempenho do sistema. Foi proposto um modelamento teórico para a PMD em fibras ópticas, baseado no comportamento observado nos novos emuladores de PMD ccom comprimento de acoplamento aleatório. / [en] A complete study of polarization mode dispertion (PMD) in optical fibers is presented. A new class of PMD emulators with random mode coupling lengths is proposed and compared experimentally and theoretically with other emulators exinting measurements, based in a optical filter transfer function is also presented and compared with the preceding method.With this new method the time domain spectral characteristics of some high frequency modulated DFB lasers were measured. First and second order PMD effects in high speed digital transmission were evaluated through both temporal distortion and power penalties measurement. The statistical treatment of the power penalties was discussed, showing that signal distortion by PMD may eventually improve the performance of the system. A theoretical model of simulate the signal propagation along the fiber was porposed, based on the emulator conception with random coupling lengths.

The growth of data capacity in optical communications links, which form the critical backbone of the modern internet, is facing a slowdown due to fundamental nonlinear limitations, leading to an impending "capacity crunch" on the horizon. Current technology has already exhausted degrees of freedom such as wavelength, amplitude, phase and polarization, leaving spatial multiplexing as the last available dimension to be efficiently exploited. To minimize the significant energy requirements associated with digital signal processing, it is critical to explore the upper limit of unmixed spatial channels in an optical fiber, which necessitates ideally packing spatial channels either in real space or in momentum space. The former strategy is realized by uncoupled multi-core fibers whose channel count has already saturated due to reliability constraint limiting fiber sizes. The later strategy is realized by the unmixed multimode fiber whose high spatial efficiency suggest the possibility of high channel-count scalability but the right subset of mode ought to be selected in order to mitigate mode coupling that is ever-present due to the plethora of perturbations a fiber normally experiences. The azimuthal modes in ring-core fibers turn out to be one of the most spatially efficient in this regard, by exploiting light’s orbital angular momentum (OAM). Unmixed mode counts have reached 12 in a ~1km fiber and 24 in a ~10m fiber. However, there is a fundamental bottleneck for scalability of conventionally bound modes and their relatively high crosstalks restricts their utility to device length applications. In this thesis, we provide a fundamental solution to further fuel the unmixed-channel count in an MMF. We utilize the phenomenon of topological confinement, which is a regime of light guidance beyond conventional cutoff that has, to the best of our knowledge, never been demonstrated till publications based on the subject matter of this thesis. In this regime, light is guided by the centrifugal barrier created by light’s OAM itself rather than conventional total internal reflection arising from the index inhomogeneity of the fiber. The loss of these topologically confined modes (TCMs) decreases down to negligible levels by increasing the OAM of fiber modes, because the centrifugal barrier that keeps photons confined to a fiber core increases with the OAM value of the mode. This leads to low-loss transmission in a km-scale fiber of these cutoff modes. Crucially, the mode-dependent confinement loss of TCMs further lifts the degeneracy of wavevectors in the complex space, leading to frustration of phase-matched coupling. This thus allows further scaling the mode count that was previously hindered by degenerate mode coupling in conventionally bound fiber modes. The frustrated coupling of TCMs thus enables a record amount of unmixed OAM modes in any type of fiber that features a high index contrast, whether specially structured as a ring-core, or simply constructed as a step-index fiber. Using all these favorable attributes, we achieve up to 50 low-loss modes with record low crosstalk (approaching -45 dB/km) over a 130-nm bandwidth in a ~1km-long ring-core fiber. The TCM effect promises to be inherently scalable, suggesting that even higher modes counts can be obtained in the future using this design methodology. Hence, the use of TCMs promises breaking the record spectral efficiency, potentially making it the choice for transmission links in future Space-Division-Multiplexing systems. Apart from their chief attribute of significantly increasing the information content per photon for quantum or classical networks, we expect that this new light guidance may find other applications such as in nonlinear signal processing and light-matter interactions.

This research paper discusses the design evaluation and selection of a transmission system to be used in checking out the Spacelab high rate data system. The transmission systems evaluated are discussed, as well as the criteria utilized in selecting the final system. The installation of a fiber optics cable and the testing of this cable are discussed. The determination of the optimum location of the high rate data bit synchronizer and Viterbi decoder is presented. Utilization of this data to justify the installation of a shorter fiber optics system inside the O&C Building is presented.