$14\mathrm{.}6$ Consider the data shown in Fig. $14\mathrm{.}37$ of the group delay versus wavelength for a $10-km$ long fiber. From this data, plot the chromatic dispersion $D$ as a function of wavelength. What is the value of the zero$-$dispersion slope $S_0$ in the relationship $D()=S_0(-{}_0)?$

Fig. $14\mathrm{.}37$ Chromatic$-$dispersion measurement of a $10-km$ fiber