The index profile of a core of multimode graded index fiber is given by?

A. $$N\left( r \right) = n1{\left[ {1 - 2\Delta {{\left( {\frac{{{r^2}}}{a}} \right)}^2}} \right]^{\frac{1}{2}}};r < a$$

B. $$N\left( r \right) = n1{\left[ {3 - 2\Delta {{\left( {\frac{{{r^2}}}{a}} \right)}^2}} \right]^{\frac{1}{2}}};r < a$$

C. $$N\left( r \right) = n1{\left[ {5 - 2\Delta {{\left( {\frac{{{r^2}}}{a}} \right)}^2}} \right]^{\frac{1}{2}}};r > a$$

D. None of the above

Answer: Option A