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Digitally selected electronically switchable terahertz-over-fibreKhairuzzaman, Md January 2014 (has links)
The Quantum Cascade Laser (QCL)-based terahertz-over-fibre (ToF) concept combines the strength of QCLs as ultra-wide bandwidth, high speed data sources, with the mature optical fibre technology. In this thesis, for the first time, by fusing multiple technologies, digitally selected, electronically-switchable ToF concept is experimentally demonstrated. Furthermore, the digital mode selection principle and electronic tuning mechanism provided by novel aperiodic distributed feedback (ADFB) multi-band filters are presented. For the development of electronically tunable ADFB lasers, a range of bound-to-continuum and chirped superlattice terahertz (THz) QCLs are measured across the frequency range 2.9 – 4.5 THz. The availability of these active materials allowed rapid assessments of the optimum design parameters for subsequent measurements. First, a range of photonic lattice-engineered lasers operating at 4.4 THz are characterized and key design parameters identified. Following this initial development, full electrical and spectral characterization of ADFB lasers operating at 2.9 THz are presented. The novelty of this work lies in the first-ever successful demonstration of discretely tunable QCLs, operating at six distinct THz frequencies. The ADFB technology was experimentally applied using various device geometries and gain dynamics. Toward this aim, results are presented for a Y coupled QCL architecture, showing that complex on-chip signal manipulation can be extended into the THz regime. In addition, it is demonstrated that ADFB technology provides broadband multi-channel optical filtering for the entire gain bandwidth. It is shown that discrete, purely electronic, tuning of simultaneous dual colour output can be achieved. Multi band optical filter functions derived from ADFB gratings possess highly nonlinear dispersion across the filter bandwidth and are found to modify the gain-induced, driving current-dependent continuous mode tuning. This thesis, therefore, presents a systematic experimental analysis of the dispersion engineered continuous fine-tuning in THz QCLs. In the final two chapters, the thesis presents, for the first time, transmission of tunable THz signals over standard single-mode optical fibre by up converting 2.9 THz QCL radiation via intra-cavity nonlinear mixing with an optical fibre-injected near-infrared (NIR) carrier in the 1.3 µm band. Discrete and continuous tuning technologies, as developed in chapters 3 – 5, are now successfully transferred to THz sidebands on the NIR carrier, extracted via a butt coupled single mode fibre and recorded using an optical spectrum analyzer. The major novel outcome of this thesis is the first demonstration of electronically tunable phase-matched points in a THz plasmon waveguide. The key breakthrough is the experimental confirmation of the photonic band-gap engineering of group velocity of THz signals – as both ‘fast’ and ‘slow’ switchable side bands are observed. Such novel nonlinear up-conversion of spectrally flexible THz signals may open up new possibilities for ultrafast THz telecom frameworks.
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Realce Automático de Imagens Subaquáticas em Rios da AmazôniaRodrigues, Daily Daleno de O. 27 February 2015 (has links)
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Previous issue date: 2015-02-27 / FAPEAM - Fundação de Amparo à Pesquisa do Estado do Amazonas / The enhancement of underwater images in applications in the area of Amazonian rivers has
been increasingly required and needs further study especially where the rivers have high
turbidity and low light. There is increasingly demand for automatic enhancement methods to
carry out monitoring of fauna and flora intensive rivers, as well as for the maintenance of
pipelines and underwater cables. The enhancement methods specified, developed and
validated for using in the rivers of the Amazonia are faced with the problem of imaging
quality. The research related to underwater am environments of the Amazon has to dead with
high turbidity of the water, caused mainly due to particles in suspension and interaction of
light with the environment. The underwater images extraction with satisfiable visibility of the
environments of Amazonian rivers has become extremely indispensable and relevant, given
that there are natural treasures still unexplored into the depths of these rivers, as well as there
is need to maintain the underwater part of the transportation system gas LPG (Liquefied
Petroleum Gas) Coari-Manaus. Given this promising scenario, this study aims to improve
these images by applying techniques of enhancement using nonlinear filters, which promote
the minimization of the light interaction characteristics with the environment, loss of contrast
and color in images extracted from turbid underwater environments. The method was
experimentally validated with images acquired from simulations of underwater scenes and
images acquired in outdoor underwater environments. The proposed method is compared to
two other techniques of highlighting or enhancement of images. As in this study, these
techniques also require a single image as input. The results return images with enhanced
visual quality, considering a large set of experiments with simulation data and real outdoors
scenes. / O realce de imagens subaquáticas em aplicações na região dos rios amazônicos é cada vez
mais requisitado e carece de um estudo mais aprofundado especialmente nos casos em que os
rios apresentam alto índice de turbidez e baixa luminosidade. Estes rios têm demandado cada
vez mais métodos de realce automáticos que realizem o monitoramento de sua fauna e flora,
bem como manutenção de dutos e cabos subaquáticos. Os métodos de realce especificados,
desenvolvidos e validados para uso nos rios da região, se deparam com o problema da
qualidade de captação de imagens. As pesquisas relacionadas aos ambientes subaquáticos da
Amazônia são prejudicadas pelo alto nível de turbidez de suas águas, causadas principalmente
devido às partículas em suspensão e à interação da luz com o meio. A extração de imagens
subaquáticas de visibilidade adequada aos ambientes dos rios amazônicos em geral, tem se
demonstrado imprescindível e relevante, haja vista que, existem tesouros naturais ainda
inexplorados nas profundezas desses rios. Por outro lado, verifica-se a necessidade de
manutenção da parte subaquática do sistema de transporte de gás GLP (Gás Liquefeito de
Petróleo) Coari-Manaus. Diante deste cenário promissor, este trabalho objetiva a melhoria
dessas imagens através da aplicação de técnicas de realce com uso de filtros não lineares, que
promovam a minimização das características da interação da luz com o meio, perda de
contraste e cores em imagens extraídas de ambientes subaquáticos turvos. O método proposto
é comparado a duas outras técnicas de realce ou melhoria de imagens que, como neste
trabalho, também requerem uma única imagem como entrada. Os resultados obtidos retornam
imagens com melhor qualidade visual, considerando-se um grande conjunto de experimentos
realizados com dados de simulação e cenas reais obtidas em ambientes externos.
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