question_answer

What should be the maximum acceptance angle at the air-core interface of an optical fibre if and are the refractive indices of the core and the cladding, respectively?

A) \[{{\sin }^{-1}}\,\left( {{n}_{2}}/{{n}_{1}} \right)\]      

B) \[{{\sin }^{-1}}\,\sqrt{n_{1}^{2}-n_{2}^{2}}\]

C) \[\left[ {{\tan }^{-1}}\frac{{{n}_{2}}}{{{n}_{1}}} \right]\]                   

D)  \[\left[ {{\tan }^{-1}}\frac{{{n}_{1}}}{{{n}_{2}}} \right]\]

Correct Answer: B

Solution :

When light is launched at one end of a step index optical fibre, then the illustration of the path of light ray incident on the end of an optical fibre at an angle to the fibre axis is as shown Acceptance angle is the maximum angle that a light ray can have relative to the axis of the fibre and propagate down the fibre. It is given by    \[\theta ={{\sin }^{-1}}\,\sqrt{n_{1}^{2}-n_{2}^{2}}\]