Question

11. A laser beam enters a fibre optic cable as shown in the cross-section below. The core of the cable has index of refrac- tion n2 and is surrounded by cladding with index of refraction n3. ni = 1.00 is the index of refraction of air. If 01 = 63.1° and 02 = 20.6°, what is the maximum value of n3 for which the beam undergoes total internal reflection and propagates down the cable? (ans. 2.37] n N₃ n, 2.82

Answer 1

Refractive index of air, na is -9003) na ma --oct → using Snell's law at air-core interface msina Masino → Mor neonat. IX sin83.10 - 2.534, Sino Sin 20-60 Now apply snell's law at core-cladding inderfece - For Mylin_90-03) = mg sin 03. total internal regration O2=90° Mga ma sin(90-2006) - 2.534 Cos 2006 Singoosa MAX M3, max = 2.372 € maximum value of mo.