Question

A multimode fiber has a core diameter of 70 micro meter and relative refractive index difference of 1.5%. It operates at the wavelength of 0.85mm. The refractive index of the fibre is 1.46. Calculate the refractive index of the cladding and normalised frequency V number of fiber.

Answer 1

Total number of modes in a multimode fiber is given by

$M=\frac {1}{2}[\frac{\pi d}{\lambda}.NA]^2$

d is the diameter

$d= \frac {1.3\times10^{-6}\sqrt2\times1100}{\pi \times 0.21213}$

$m=91.5\mu m$