Numerical Calculation of Optimum a for a Germania-Doped Silica Lightguide

It is now well established that a lightguide with a near parabolic index profile can have single frequency bandwidths of 1 GHz-km or greater.1-3 This is expected to happen if the profile is smooth, the central dip is narrow or small, the profile parameter is properly chosen, and modes that have a significant amount of their energy transported in the cladding are eliminated.4"6 Our understanding of these factors has largely come from approximate solutions to Maxwell's equations for lightguides. The availability of computer software for exact numerical solutions7 to Maxwell's equations allows us to reexamine some of these effects and to look at other factors that may influence lightguide bandwidths. In this paper, we determine optimum power law profile parameters (i.e., a parameters) as a function of wavelength for a germania-doped silica lightguide.