Evaluation of longitudinal chromatic dispersion

The relationship between changes in the refractive index along a fiber and chromatic dispersion is investigated theoretically. The variance of the chromatic dispersion along a fiber is approximately proportional to that of longitudinal structural fiber parameters. To control the dispersion to within ±1 ps/km/nm, theoretical results indicate that the longitudinal deviations of the core radius and relative index difference must be less than 0.04 μm and 0.014%, respectively, for W-type dispersion-flattened fiber. Measurements of the standard deviation of the change in the longitudinal parameter for W-type dispersion-flattened fiber fabricated by the vapour axial deposition VAD method show that chromatic dispersion deviation is mainly caused by longitudinal core radius deviation. The effective standard deviation of the core radius is estimated to be within 0.03 μm