Question

A step index fibre has a relative refractive index of 0.88%. What is the critical angle at the core cladding interface?

• A. ${60}^0$
• B. ${75}^0$
• C. ${45}^0$
• D. None of these

Answer 1

The correct option is D None of these

Given,

Relative refractive index $=0.88\%$

$\Rightarrow \frac{{\mu }_1-{\mu }_2}{{\mu }_1}=\frac{0.88}{100}$

$\Rightarrow 1-\frac{{\mu }_2}{{\mu }_1}=\frac{0.88}{100}$

$\frac{{\mu }_2}{{\mu }_1}=1-\frac{0.88}{100}$

$\frac{{\mu }_2}{{\mu }_1}=0.9912$

Critical angle, ${\theta }_c={\sin }^{-1}\left(\frac{{\mu }_2}{{\mu }_1}\right)$

$={\sin }^{-1}\left(0.9912\right)$

${\theta }_c={82.3}^{o}C$