Scattering from an off-axis inhomogeneity in step-index optical fibers: radiation loss

An exact analysis using the Green’s function formulation of an arbitrarily oriented off-axis dipole in a three-layer cylindrical dielectric waveguide is carried out. The practical significance of such a formulation is illustrated by its immediate application to the problem of radiation due to scattering from an arbitrarily located discrete inhomogeneity in step-index fibers in which the dominant HE11 mode propagates. For small dielectric differences between the adjacent layers, the analysis yields radiation loss that agrees well with that evaluated from the infinite-medium approximation. However, the spatial distribution of the radiation loss differs markedly from that predicted by the infinite-medium approximation.