An investigation into the production of low-loss optical fibres from organic polymers
This thesis reports the investigation and analysis of the optical properties of organic polymers in the context of their use as materials for low-loss optical fibres. The use of novel polymers, for example amorphous perhalopolymers and both fluorinated and deuterated acrylics, has been considered. These materials possess distinct advantages over more conventional polymers, in terms of both improved high-temperature resistance and reduced optical attenuation. However, further investigation was impractical because neither suitable monomer nor polymers were available. Thus, the bulk of this work is concentrated on the traditional polymer glasses of polymethylmethacrylate (PMMA) and polystyrene (PS). Two techniques for the fabrication of polymer optical fibres have been studied; preform drawing and melt extrusion. In the initial experiments, rods of commercially produced PMMA were drawn into fibres. Although the technique itself showed promise, the work was suspended because of the poor and variable optical quality of the available polymer rods. The minimum attenuations achieved varied between 2400dB/km and in excess of 20,000dB/km, depending on the quality of the rod, or region of the rod, concerned. In the light of the findings of these initial studies, an integrated fabrication system was developed. The system is based on melt extrusion and combines monomer purification, polymerization and fibre production within an essentially enclosed apparatus. This system has been proved capable of producing PS-cored, ethylene vinylacetate copolymer-cladded fibres with minimum losses of 154dB/km at 672nm. The geometric quality of the fibre is also good, with values of core diametric variation and core-cladding concentricity of better than ±0.5% and 1.3:1 respectively.