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Optical fibre

(a) Describe the terms of reflection, absorption, and transmission with suitable diagrams. Present and explain the relationship between reflection, absorption and transmission coefficients. Describe the differences between materials that are opaque translucent and transparents.
(b) An optical fibre consists of a core of refractive index 1.667 surrounded by a cladding of refractive index 1.523. The refractive index of air is 1.000. (See the question sin the attachment to see figures and questions to calculate).
(c) The visible electromagnetic spectrum is defined to range from blue light of wavelength 400nm through to red light of wavelength 700nm. A light-emitting dioxide display made using GeAs-GaP emits photons with the energy E=1.8eV. Find the wavelength of the light and answer whether it is closer to the blue light or red lights.
(d) A pulse of white light is sent straight down a fibre optic cable 1km long the refractive index to the blue light or red light. (see attachment for further calculations).


Solution Preview

4a. Incident radiation energy (Qi) on a surface of a body, partly gets absorbed (Qa) by the body, partly reflected (Qr) and partly transmitted (Qt) through the body (see attached Figure).

Qi = Qa + Qr + Qt

Divided by Qi both the sides,
1 = Qa/Qi + Qr/Qi + Qt/Qi
=> a + r + t =1
a = Qa/Qi == absorption coefficient: fraction of incident radiation energy which gets absorbed by the body.
r = Qr/Qi == reflection coefficient: fraction of incident radiation energy which gets reflected by the body.
t ...

Solution Summary

There are two parts: 1. understanding reflection, refraction and absorption, 2. A numerical problem related to transmission of light through fibre optics.