Accuracy of approximate methods for the evaluation of chromatic dispersion in dispersion-flattened fibers

The accuracy of three approximate methods of estimating chromatic dispersion in dispersion-flattened fibers is examined. In these methods, the material dispersion of fiber is approximated by (a) the dispersion of pure fused silica, (b) the dispersion of the core material, and (c) the weighted average of material dispersion of various layers of the fiber. The actual values and three approximate values of the dispersion are calculated and compared for fibers with two, three, and four cladding regions. Examples of satisfactory and poor accuracy are given. The accuracy of approximate methods depends on the index differences and their first- and second-order derivatives with respect to wavelength. The smaller the index differences and their derivatives, the smaller the error in the approximate dispersion. However, small index differences along do not guarantee small errors. For GeO₂-doped fibers, the accuracy of approximate methods b and c is much better than that of method a