Scattering from an off-axis inhomogeneity in step-index optical fibers-mode conversion

There is much current interest in dielectric surface waveguides due to their important applications in fiber communication systems. Many theoretical and practical problems are involved. An important problem is the excitation of surface waves and radiation by an infinitesimal dipole in cylindrical dielectric waveguides. The excitation of surface waves has been previously treated by employing the Lorentz reciprocity theorem [1,2] involving the use of the orthogonality relations in the modal fields. This technique, however, does not yield any information about the radiation fields. For waveguides with small dielectric differences between the adjacent layers, the radiation loss due to a localized impurity can be evaluated by the infinite-medium approximation [3]. This method does not yield any information about the surface waves. Yip [4] investigated the excitation of the mode by a transversely-oriented infinitesimal dipole on the axis of a rod, and the resulting formulation was later [5] used to calculate the radiation loss due to scattering from an on-axis inhomogeneity in a cladded fiber optical waveguide.