Abstract
Multiple-beam Fizeau fringes in transmission and at reflection were applied to the study of the optical properties of fibres with irregular cross-section (
Orlon 42 and nylon fibres). The mathematical expressions used for the application of multiple-beam Fizeau fringes to determine the refractive indices and birefringence of fibres are given. The experimental techniques used for producing multiple-beam Fizeau fringes in transmission and at reflection are also given. Interferometric methods were applied to study the variation of refractive indices with wavelength of light and along the fibre axis. Values of refractive indices were used to calculate Cauchy's dispersion constants. The value of thermal coefficient of refractive index has been calculated. Illustrations are given using multiple-beam interferograms.