Telecommunication-introduction

Introduction
The use of light to send messages is not new. The idea of using glass fibre to carry an optical communications signal originated with Alexander Graham Bell. However this idea had to wait some 80 years for better glasses and low-cost electronics for it to become useful in practical situations.
Fiber-optic communications is based on the principle that light in a glass medium can carry more information over longer distances than electrical signals can carry in a copper or coaxial medium. With few transmission losses, low interference, and high bandwidth potential, optical fiber is an almost ideal transmission medium.
Among the tens of thousands of developments and inventions that have contributed to this progress three stand out as milestones:
1. The invention of the LASER (in the late 1950's)
2. The development of low loss optical fibre (1970's)
3. The invention of the optical fibre amplifier (1980's)
In initial time, portion of electro magnetic spectrum was used to convey information in communications systems.
The data is transferred over the communication channel by superimposing the information onto a sinusoidally varying electromagnetic wave, which is known as “carrier”.
At the destination information is removed from the carrier wave and processed as desired.
More the information to be carried, higher the carrier frequency there by increasing the transmission bandwidth.