Abstract
The structural properties, mainly the spatial variation of density and chain interaction, of melt-spun polymer optical fibres (POFs) are investigated by small-angle X-ray scattering (SAXS) and compared to Monte-Carlo polymer simulations. The amorphous PMMA POFs had been subjected to a rapid cooling in a water quench right after extrusion in order to obtain a radial refractive-index profile. Four fibre samples with different processing parameters are investigated and the SAXS data analysed via Guinier approach. Distance-distribution functions from the respective equatorial and meridional SAXS data are computed to extract the fibres’ nanostructures in the equatorial plane and along the fibre axis, respectively. Temperature profiles of the cooling process are simulated for different locations within the fibre and taken as input for Monte-Carlo simulations of the polymer structure. The simulation results agree with the SAXS measurements in terms of the cooling profile’s strong influence on the structural properties of the fibre: slower cooling in the centre of the fibre leads to stronger interchain interaction, but also results in a higher density and more homogenous materials with less optical scattering.
Highlights
Most large-core polymer optical fibres (POF) are made from poly-methyl methacrylate (PMMA)
The simulation results agree with the small-angle X-ray scattering (SAXS) measurements in terms of the cooling profile’s strong influence on the structural properties of the fibre: slower cooling in the centre of the fibre leads to stronger interchain interaction, and results in a higher density and more homogenous materials with less optical scattering
Four PMMA-POFs produced with different sets of process parameters were reinvestigated with small-angle X-ray scattering and compared to polymer Monte-Carlo simulations of the cooling
Summary
Most large-core polymer optical fibres (POF) are made from poly-methyl methacrylate (PMMA). Depending on the kind of application, POFs should show different properties, such as controlled scattering for illumination and sensing or relatively low attenuation and small mode dispersion for data communication. For the latter, graded-index (GI) fibres have been developed with a decreasing refractive-index profile towards the outer regions of the fibre [2,3,4]. Different cooling rates of inner and outer regions result in a radial density gradient, which leads to a refractive-index profile. A Monte-Carlo simulation of the cooling of PMMA was performed for the different temperature profiles and the resulting structural properties analysed.
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