Question

The refractive indices of the core and cladding materials of an optical fibre are 1.64  and 1.53 respectively. Calculate the numerical aperture and light gathering capacity  of the fibre.

Answer 1

$NA=\sqrt{n_2^2-n_1^2}=\sqrt{1.64^2-1.53^2}=0.59,$

$\theta=\arcsin \frac{n_1}{n_2}=\arcsin\frac{1.53}{1.64}=68.9°.$