Abstract
In this paper, we used lens-fibre interference technique, proposed by Ramadan (J Opt A: Pure and appl Opt 2 (2000) 234) to determine the refractive index of the step-index fibre core with radius of the order of 0.85
mm. A mathematical expression for the optical path length has been derived and used to estimate the obtained experimental interference fringes. A comparison between the experimental and theoretical fringes provides the refractive index of the fibre-core material. This comparison has been done with the aid of computer image processing to increase the accuracy of our measurements. The accuracy in the measured refractive index is of the order of ±8×10
−4.