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Question 1: The core of an optical fiber is made from flint glass (nfint = 1.667) and is surrounded by cladding made from crown glass (ncrown = 1.523). A light ray enters the fiber at an angle of incidence of 0. What is this value of O, if the light strikes the core-cladding interface at the critical angle? Cladding Core Air

Answer 1

! B Cladding Air Core --^ _ P2_

At Point B:

Using Snell's law

n_core Sin$\theta _{c}$ = n_cladding Sin90

n_flint Sin$\theta _{c}$ = n_crown Sin90

(1.667) Sin$\theta _{c}$ = (1.523) Sin90

Sin$\theta _{c}$ = 0.914

$\theta _{c}$ = Sin^-1(0.914)

$\theta _{c}$ = 66.06 deg

In triangle ABC

$\theta _{2}$ = 90 - $\theta _{c}$

$\theta _{2}$ = 90 - 66.06

$\theta _{2}$ = 23.94 deg

Using Snell's law at A

n_air Sin$\theta _{1}$ = n_core Sin$\theta _{2}$

(1) Sin$\theta _{1}$ = (1.667) Sin23.94

$\theta _{1}$ = Sin^-1((1.667) Sin23.94)

$\theta _{1}$ = 42.6 deg