Question

For a step index fibre with a core of refractive index of 1.54 and cladding refractive index 1.5 calculate the following when fibre is kept in water

b)Numerical aperture

c)Acceptance angle

d)Numerical Aperture in air

Answer 1

Core refracting index, $\mu_1=1.54$

Cladding refracting index, $\mu_2=1.50$

Refractive index of air, $\mu_o=1$

(b) Numerical Aperture, $(NA)=\sqrt{\mu_1^2-\mu_2^2}$

$=\sqrt{(1.54)^2-(1.50)^2}=0.348$

(c) Acceptance angle, $\theta_a=sin^{-1}(NA)=sin^{-1}(0.348)=20.40\degree$

(d) Numerical aperture in air $=\sqrt{\mu_1^2-\mu_o^2}$

$=\sqrt{(1.54)^2-1^2}=1.17$