On the determination of the refractive index of a fibre: I. Skin-core fibre

Abstract

Two- and multiple-beam interferometric methods are used to study the refractive index profiles of cylindrical fibres having skin-core structure. The refraction of the incident beam inside the fibre is considered. Mathematical expressions are derived for this aim, and applied with two- and multiple-beam microinterferograms of cuperamonium, polypropylene, Roman nylon-6 (synthetic polymer fibres) and step index optical fibre. A comparison between the results and that in the case of non-distorted immersed wavefront is dealt with. The application of the derived expressions results shows a good correction of the results due to the mismatching effect. Microinterferograms are given for illustration.