Answer to Question #167988 in Optics for Yeboah Bridget

Question

• Compute the number of modes that will be 

supported by a fibre with core diameter of 20mm, a 

core refractive index of 1.5 and a cladding index of 

1.48 if it is excited by light of frequency 0.25MHz

Answer 1

Answer

Given radius of core

a=$D/2$ =0.01m

$n_1=1.5\\n_2=1.48$

Frequency f=$0.25\times10^6Hz$

So wavelegth

$\lambda=\frac{c}{f}=1200m$

Therefore no. Of modes

$V=\frac{2\times3.14\times0.01}{1200}\sqrt{(1.5)^2-(1.48)^2}$

$=1.277\times10^{-5}$

According concepts

V$<2.405$

Therefore only one mode is possible.