AbstractThe design of optical fibre cables has for many years been a laborious manual task involving geometrical mathematics, a knowledge of materials, and past experience. The objectives of the work were to develop a series of design aids which would both automate the process of physical cable design and optimise the optical fibre performance within the cable.
The computer aided design system developed was restricted to the design of 'loose tube' fibre optic cables as this represents the main cable type manufactured by the company. Of several potential computing methods, an expert-system-shell was chosen as this presented the most effective way to harness all relevant information. The resulting knowledge base enables a user to design any variation of a 'loose-tube' cable, and obtain immediate data regarding its weight and dimensions. The expert-system was interfaced to software which subsequently generates a cross-sectional diagram of the eventual cable.
To optimise fibre performance within a cable, an investigation was made of the fibre overfeed or excess within the 'loose-tubes'. Too little excess may cause excessive fibre strain, whilst too much may result in fibre bends below a critical radius. As fibres become very lossy below this radius, experiments were performed to quantify this phenomenon. Comparisons were made between four commercially available fibre types, and the results found the Chemical-Vapour-Deposition, depressed cladding fibre type, to be the most bend-insensitive.
The expert system to design cables is fully functional within the technical department, and is estimated to save over 4000 man-hours per annum. Software has also been written to relate the maximum working tensions of a cable to the fibre excess, whilst the experimental results on fibre bend characteristics are presented in graphical form.
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