Fizeau interferometry-based measurement of the photo-elastic coefficient and the cut-off wavelength in bent standard single-mode optical fiber

Abstract

New technique based on multiple-beam Fizeau fringes to study the influence of bending on a standard single-mode optical fiber which has a total minimum dispersion at 1.31 μm, is described. The technique is used to determine some of the single-mode optical fiber properties such as the photo-elastic coefficient of the cladding material. Estimation of the cut-off wavelength is needed to support the propagation of the fundamental HE ∥ mode in the bent fiber is investigated. The mathematical analysis to describe the fringe shifts in case of a matching and a non-matching liquid wedge interferometer is given. Mathematical expressions to determine the photo-elastic coefficient and the cut-off wavelength from the interference fringe shift due to bending are derived. The determined value of the photo-elastic coefficient is 0.229, which is in good agreement with the literature. In a regime of curvature between 7.5 and 19 mm, three additional modes are allowed to be guided due to the decrease of the cladding index in the tensile region. Micro-interferograms are given for illustration.