A general power-series expansion method for scalar analysis of the guided modes in an optical fiber

A power-series expansion method for approximate analysis of the guided modes in a cylindrical, radially inhomogeneous dielectric waveguide is presented. The method is developed for a piece-wise polynominal permittivity profile. The solution of the scalar wave equation is constructed by a sequence of power-series expantions. Convergence is ensured and accuracy maintained by regulating the distance (= the steplength ) between successive expansion points. It is demonstrated, by analytical reasoning and numerical examples, that a short steplength is insufficient. The characteristic equation and the cutoff condition are expressed in a unified manner. The method presented is competetive in terms of accuracy achieved and computing time required