Theoretical and experimental treatments of the shape of Fizeau fringes
crossing a fiber of nearly triangular shaped cross-section assumed to consist of
a single medium are presented. A new mathematical expression is derived and
used to estimate the refractive indices and birefringence of nylon 6
(polycaprolactam). The resulting data are used to calculate the volume
polarizabilities per unit. Cauchy's dispersion constants, the isotropic refractive
indices and the variation of refractive indices due to annealing process. Also
other optical parameters obtained are calculated. Illustrations are given using
micro-interferograms and curves.