Coherent light scattering measurements on single and cladded optical glass fibres

Abstract
This paper considers the scattering, at normal incidence, of a laser beam by single and cladded optical glass fibres with a view to estimating their radii and refractive indices. For parallel and perpendicular polarizations of the incident light, the scattered intensity was calculated using the wave theory. The scattering pattern from a single fibre was also calculated by geometrical optics. The light scattered by a cladded fibre in air was photographed for fibres of three different overall diameters. A similar experiment was conducted for the fibre immersed in a liquid having a refractive index near to that of the cladding. Matching was achieved by thermal means.In both cases considered, the experimental results were found to be in agreement with theoretical results. For a cladded fibre in air, information about the core could not be obtained but a measurement of the angular fringe spacings and positions enabled the cladding diameter and index to be calculated. For a cladded fibre immersed in an index matching liquid, it was found that a measurement of the angular positions of minimum intensity enabled the core diameter to be calculated.

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