Accurate prediction of the propagation characteristics of single-mode graded-index fibers by a novel approximation of the fundamental modal field

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We propose a novel approximation of the fundamental modal field in single-mode graded-index fiber and present a variational analysis to investigate the propagation parameters of practical interest. Employ- ing the formulated fundamental modal field, we prescribe analytical ex- pressions for normalized Petermann I spot size, group delay, and modal dispersion parameter for single-mode graded-index fiber. With the ex- amples of step- and parabolic-index fibers, we show that these param- eters as evaluated by our formalism match excellently with the available exact ones over a wide range of V values. Particularly in the low V region, where the Gaussian approximation is not accurate, our results are found to predict the propagation characteristics accurately. Thus the validity of our formalism is justified. Much less computation is required than with previous methods. The approximation will be useful in the analysis of nonlinear and doped-fiber amplifiers. © 2002 Society of Photo-