On the microinterferometric determination of refractive indices and birefringence of fibres

Abstract

The paper deals with the determination of refractive indices and birefringence of polymer fibres using both two- and multiple-beam microinterferometry. Different techniques of interferometry are given together with their applications in investigating the optical properties of fibres. An analysis of the microinterferograms of fibres with irregular transverse sections is given. The optomechanical properties of polymer fibres, measured dynamically by interferometry, are dealt with. Lateral birefringence of fibres is also given. A mathematical expression is derived to determine the refractive indices, birefringence and the index profile of a cylindrical fibre taking into consideration the refraction of the incident beam by the fibre. This expression is applied with the two-beam microinterferograms produced for polypropylene fibres. A comparison between the two- and multiple-beam microinterferometric methods for the determination of refractive indices and birefringence of fibres is given. Both methods are evaluated. Microinterferograms are given for illustration.