Propagation loss in metal-clad waveguides and weakly absorptive waveguides by a perturbation method.

A simple and accurate perturbation method for the analysis of attenuation of guided modes in metal-clad waveguides and weakly absorptive waveguides is presented. The imaginary part N'' of the complex modal index N = N' + iN'' is obtained by solving the corresponding real eigenvalue equation and is given by partial differentialN'/ partial differentialepsilon' times epsilon'', where epsilon = epsilon' + iepsilon'' is the complex dielectric constant of the absorptive layer and partial differentialN'/ partial differentialepsilon' is obtained by numerical differentiation. The method is straightforward, and a cumbersome solution of complex transcendental equations is completely eliminated. Results for simple structures are in good agreement with those obtained by exact analysis.