Abstract
A modified method using multiple-beam Fizeau fringes is used to measure refractive indices of immersion liquids. In this case, there is no need for making corrections for the temperature and dispersion of these liquids. This method is applied to determine the refractive index profile of a cylindrical multilayer fibre. A mathematical formula is derived in the case of the shape of multiple-beam Fizeau fringes crossing a cylindrical multilayer fibre, as well as equations to determine the refractive index profile for fibre having irregular cross section. Similar mathematical formulas are derived for the case of fibre having skin-core structure. This method with the derived equations is applied to determine the optical properties of “Terylene” and polypropylene fibres. Microinterferograms are given for illustrations.
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