Determining the optical properties of highly oriented fibres using a multiple-beam technique

Mathematical formulae are modified for the shape of multiple-beam Fizeau fr inges in transmission to determine the mean refractive indices and birefrin gence of highly oriented fibres. These modified mathematical formulae are a pplied with the multiple-beam interference method to determine the optical anisotropy of polypropylene fibre with a draw ratio of 3.5. The refractive indices and birefringence results are compared with those obtained using th e conventional method and are found to be in good agreement. The new method is also applied for (poly(ethylene 2,6-naphthalene-dicarboxylate), 1000 de nier/248 filaments, PEN-Q50M4 (PEN) and poly(ethylene terephthalate) 1000 d enier/250 filaments, PET-BHT, highly oriented yam, Teijin, Japan (PET)) hig hly oriented fibres. Illustrations are given through microinterferograms.