Interferometric determination of propagation constant difference between adjacent propagated modes in bent GRIN optical fibres

Bending induces an optical anisotropy in optical fibres, changing their optical properties. In this work, we present a new interferometric-based method in order to evaluate the influence of bending on the propagation constant difference between two adjacent propagated modes in terms of core–cladding index-difference variation. In this method, multiple-beam Fizeau fringes at transmission are obtained through a bent GRIN fibre determining the core–cladding index difference versus radius of curvature from fringe patterns. Micro-interferograms are presented.