Question

• In an optical fibre, the core material has refractive index 1.8 and refractive index of clad
material is 1.6. What is the value of critical angle?
Answer
A.O 89.62 Degree
CO 62.62 Degree
B.O 98.42 Degree
DO 42.72 Degree
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Answer 1

. The refractive indices of core and cladding materials of a step index fibre are 1.48 and 1.45, respectively. Calculate: (i) numerical aperture, (ii) acceptance angle, and (iii) the critical angle at the core-cladding interface and (iv) fractional refractive indices change.

(Set-1–May 2006)

Sol: Let the refractive index of core, n1 = 1.48

and the refractive index of cladding , n2 = 1.45

Numerical aperture (NA) images

images

Let θ0 be the acceptance angle

n2 sin 90 = n1 sin θc [θc = critical angle]

The fractional refractive ...