$7.$ Consider a $50/125$ graded$-$index fiber with n$1=1\mathrm{.}48,4=2\%$ and gopt $=2\mathrm{.}0.$

$($a$)$ Calculate the ratio of modal delay per km of the non$-$optimized graded$-$index fiber

with g $=110\%$ of gopt to the modal delay in a step$-$index fiber of the same size with the

same ni and A$.$

$($b$)$ It has been found the ratio of Atmodal g $=$ gopt to ATmodal g # gopt. for a certain fiber is $5.$

What is the percentage of deviation of g from the optimized gopt $=2\mathrm{.}0?$