ETD Collection
Permanent URI for this collectionhttps://wiredspace.wits.ac.za/handle/10539/104
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Item Towards the development of a thulium-doped all-fibre laser(2018) Kgomo, Mosima BFibre based lasers have become a dominant laser architecture due to high output powers and efficiencies, compact form factors, and excellent beam quality. Double-clad large mode area fibres (DC-LMAF) are required to achieve high output power (up to kW level). The performance and integrity of the thulium-doped all-fibre laser is critically dependent on the quality of splices between different components constituting the fibre laser. Power loss at the splice joints (splice loss) has a deleterious effect on the performance and long-term reliability of high power fibre lasers. Splice losses, caused by poor fusion splices, lead to a decrease in the optical-to-optical efficiency as well as degradation in the beam quality of fibre lasers. The low-loss, wavelength-dependent fusion splices are required for the development of the high power thulium-doped all-fibre laser that is known to lase in the 2000 nm wavelength region. A spectral splice loss measurement technique was constructed to measure splice loss between two 25/400 µm passive DC-LMAF in the 2000 nm spectral region. The different types of aspects that can lead to splice loss measurement variations are investigated and mitigated. The 0.03% was the expected splice loss measurement variation. The optimal parameter set points for fusion splicing two 25/400 µm passive DC-LMAF were found through conducting a splice loss optimization experiment. The fractional factorial design of experiment which enables the reduction of the required number of experiments by performing them at a certain specific combination of parameters was applied due to the seven large number of splice parameters that required to be optimized. A total of 18 experiments were conducted based on the fractional factorial design of experiment that followed the Taguchi orthogonal methodology. The splice loss results were analysed by using a statistical technique, the analysis of variance (ANOVA). The Gap Distance and Arc Time 2 splice parameters were revealed to be the two most important parameters that have an impact on fusion splice quality by contributing 32% and 27% towards splice loss, respectively within the chosen splice parameter levels for this work.Item Innovation-based competitive differentiation amongst South African fibre to the home (FTTH) operators(2018) Ntsandeni, AndiswaFibre-to-the-home (FTTH) as an access technology is viewed as vital for economic growth and competitiveness. The deployment of high speed networks and advanced access technologies is essential for continuous development of broadband in South Africa. FTTH is an access technology that has recently been deployed and adopted by different network providers in South Africa. South Africa is one of the developing countries attracting investments in the deployment of infrastructure where industry players are deploying fibre at a high rate with acquisition of smaller players. FTTH operators and service providers are challenged with competitive pressures within the market where competitiveness relies on the capacity to continually develop and implement unique innovative initiatives that will drive competitive advantage over its competitors. Competitive advantage is needed to achieve the organisation’s objectives. These innovative initiatives are required due to intense competition within the market which results in reduction of prices and margins. The purpose of this study is the exploration of innovation-based competitive differentiation from a South African FTTH provider perspective. The study aims to look at potential innovation differentiation amongst South African FTTH providers and how it can be applied in order to obtain a competitive advantage by looking at the factors that influence competitive advantage and barriers for innovation within the market. The study will provide knowledge and insights to develop an understanding of innovation for FTTH providers in a developing country such as South Africa. In this study, realistic data from the different network providers and service providers has been collected utilising a qualitative research method to investigate and conduct an in-depth analysis based on interviews with subject matter experts and managers from FTTH operators and service providers. Some propositions have been suggested as a validation for the proposed framework. The sample for the study has been drawn from the active FTTH network infrastructure operators and service providers based in Gauteng. The research findings indicate that the fibre-to-the-home market is a highly competitive environment with network providers and service providers offering various products and services to customers in order to meet customer needs. However, there are challenges with innovation based competitive differentiation since, currently, 3 competition is primarily based on the price of the broadband product. As a result, prices have been plummeting, leading to some service providers operating and selling their FTTH products with no margins or negative margins. KEYWORDS: Fibre-to-the-Home, FTTH, Innovation, Differentiation, Competition, Network Operators, Competitive Advantage.Item Modelling, system identification and control of a fibre optic accelerometer(2015) Cornelius, Justin CalenControl of systems are important in most industrial sectors, they nd applications in electronics, machine design and navigation. These control systems often use sensors to work e ectively. One such sensor is an accelerometer, which is used to measure acceleration with one or more degrees of freedom. This research report investigates the modelling, system identi cation and controller design for an accelerometer, a Fibre Optic Accelerometer (FOA). Such a device may be applied in many applications such as anti-skid control, structural failure in buildings and bridges, as well as strategic missile guidance. This report presents a model of a FOA demonstrator which crudely models an industrially developed accelerometer, the demonstrator is made of a jig consisting of a guitar string and electromagnets. Such a model needs to account for a distributed parameter beam combined with a permanent magnet and four electromagnets. The guitar string is modelled using three beam models, namely a spring/damper model, an Assumed Modes Model (ASM) and a Transfer Function Model (TFM). The parameters for these beam models are identi ed using the Nelder-Mead simplex algorithm and the least squares method. The electromagnets within the jig, are modelled using a mathematical model obtained through curve tting of experimental data. The overall FOA sensor is optimised using a lead-lag controller. Five cost functions where investigated, these cost functions are H1, Integral Square Error (ISE), Integral Absolute Error (IAE), Integral Time Square Error (ITSE) and Integral Absolute Time Error (IATE). It was found that the guitar string may be modelled using a single degree of freedom beam model. This is based on a number of reasons, such as the aperture size - through which the tip Light Emitting Diode (LED) projects, the tip mass (permanent magnet) - acting as a natural damper and the fact that Position Sensing Device (PSD) only measures the tip position. It was found that a single degree of freedom model in two orthogonal axes, with a single link beam spring/damper model was the most suitable representation of the guitar string. And the IAE lead-lag controller was found to be the most e ective in controlling a guitar string, this e ectiveness was due to least settling time.