Page 197 - Photonics Essentials an introduction with experiments

Source: Photonics Essentials

Chapter
9

Optical Fibers and
Optical Fiber Amplifiers

9.1 Introduction
It has been known and understood from at least the time of Isaac
Newton that light beams could be trapped and guided in a medium of
higher index of refraction material surrounded by lower index of re-
fraction material. Newton’s demonstration consisted of trapping a
light beam inside a stream of water (Fig. 9.1). Three hundred years
later we figured out how to use this observation and revolutionized
the telecommunications industry. How did it happen?
It was also known in Newton’s time that glass was transparent to
visible light and that it could be fashioned into prisms and lenses that
could be used to bend light beams through fixed angles. Glass technol-
ogy was already thousands of years old at that time. However, the
telephone was still 200 years in the future. About 50 years ago, well
after the telephone was in widespread use, interest developed in us-
ing optical fiber bundles as a way to transmit images from one place
to another. The principal applications were in the medical field for im-
aging inside the body, particularly during surgery. This work let the
cat out of the bag. One of the pioneers of fiber bundle imaging was a
young British medical student named Narinder Kapany. He soon left
medicine to promote the use of optical fibers for telecommunications
and is still working in the field. In 1966, Charles Kao at Standard
Telephone and Cable in England obtained the first results that
showed that practical communications using optical fibers might be
possible when he demonstrated an optical fiber with losses on the or-

191
Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.