Question

In a step-index optical fiber, the refractive indices of the core and the cladding are equal to 1.501 and 1.499, respectively, at the wavelength of $850\text{nm}$. The fiber is surrounded by air.

The numerical aperture of the optical fibre is

• A. 0.077
• B. 1.501
• C. 0.501
• D. 1.499

Answer 1

The correct option is A 0.077

$N.A.=\sqrt{n_1^2-n_2^2}=\sqrt{(1.501{)}^2-(1.499{)}^2}=0.077$