PH8151EPUnit1

Chapter 2

WAVES AND FIBER OPTICS

“When God said “Let there be light”

he surely must have meant perfectly

coherent light”.

Charles Hard Townes

Coinventor of maser and Physics

Nobel Laureate 1964.

Syllabus:

Oscillatory motion – forced and damped oscillations: dierential equation

and its solution – plane progressive waves – wave equation.

Lasers : population of energy levels, Einstein’s A and B coecients

derivation – resonant cavity, optical amplification (qualitative) –Semicon-

ductor lasers: homojunction and heterojunction – Fiber optics: principle,

numerical aperture and acceptance angle - types of optical fibres (material,

refractive index, mode) – losses associated with optical fibers - fibre optic

sensors: pressure and displacement.

2.1 Introduction...................................

A major objective of the present unit is to learn the physics of coherent light (laser) and its
application in communication technology (fiber optics). Light, just like any other physical
entity, exhibits wave-particle duality. As the wave behaviour light is prominently used in
laser and fiber optic applications, it is necessary to discuss the principles of the phenomena
of waves and the closely associated physics of oscillatory motions. Therefore, this chapter
consists of three related topics; Oscillations and Waves, basics of Laser Physics, and

fundamentals of Fiber Optics.

We begin our discussion ofOscillations and Waveswith a some what detailed discus-
sion of simple harmonic motion as it is the most basic type of oscillatory motion which

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