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Introduction to
Fiber Optics
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Introduction to
Fiber Optics
2nd Edition
John Crisp
OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI
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Newnes
An imprint of Butterworth–Heinemann
Linacre House, Jordan Hill, Oxford OX2 8DP
A division of Reed Educational and Professional Publishing Ltd
A member of the Reed Elsevier plc group
First published 1996
Reprinted 1997, 1998, 1999, 2000 (three times), 2001
Second edition 2001
© John Crisp 1996, 2001
All rights reserved. No part of this publication may be reproduced in any material form
(including photocopying or storing in any medium by electronic means and whether or
not transiently or incidentally to some other use of this publication) without the written
permission of the copyright holder except in accordance with the provisions of the
Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the
Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1P 0LP.
Applications for the copyright holder’s written permission to reproduce any part of this
publication should be addressed to the publishers.
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
ISBN 07506 50303
Composition by Scribe Design, Gillingham, Kent
Printed and bound in Great Britain by Biddles Ltd, www.biddles.co.uk
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Contents
Preface vii
1 Optic fiber and light — a brilliant combination 1
2 What makes the light stay in the fiber? 9
3 The choice of frequency 17
4 Propagation of light along the fiber 22
5 Decibels 39
6 Losses in optic fibers 50
7 Dispersion and our attempts to prevent it 59
8 Real cables 68
9 Connecting optic fibers — the problems 82
10 Fusion splicing 92
11 Mechanical splices 103
12 Connectors 108
13 Couplers 126
14 Light sources and detectors 139
15 Testing a system 147
16 System design — or, will it work? 166
17 The transmission of signals 183
18 Organizing optic fiber within a building 192
19 LANs and topology 200
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Contents
20 Some final thoughts 206
Glossary 210
Quiz time answers 217
Index 227
vi
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Preface
An increasing proportion of the world’s communications are carried by fiber
optic cables. It has spread quietly, almost without being noticed into every situa-
tion in which information is being transmitted whether it is within the home
hi-fi system, cable television or telecommunication cables under the oceans.
The purpose of this book is to provide a worry-free introduction to the subject.
It starts at the beginning and does not assume any previous knowledge of the
subject and, in gentle steps, it introduces the theory and practical knowledge
that is necessary to use and understand this new technology.
In learning any new subject jargon is a real problem. When the words are
understood by all parties they make an efficient shorthand form of communi-
cation. Herein lies the snag. If not understood, jargon can create an almost
impenetrable barrier to keep us out. In this book jargon is introduced only when
required and in easily digested snacks.
John Crisp
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1
Optic fiber and light — a
brilliant combination
The starting point
For thousands of years we have used light to communicate. The welcoming
camp fire guided us home and kept wild animals at bay. Signal bonfires were
lit on hilltops to warn of invasion. Even in these high-tech days of satellite
communications, ships still carry powerful lamps for signaling at sea, signaling
mirrors are standard issue in survival packs.
It was a well known ‘fact’ that, as light travels in straight lines, it is impossible
to make it follow a curved path to shine around corners.
Boston, Mass., USA, 1870. An Irish physicist by the name of John Tyndall gave
a public demonstration of an experiment which not only disproved this belief
but gave birth to a revolution in communications technology.
His idea was very simple. He filled a container with water and shone a light into
it. In a darkened room, he pulled out the bung. The light shone out of the hole
and the water gushed out.
It was expected that the light would shine straight out of the hole and the water
would curve downwards — as shown in Figure 1.1.
Now see Figure 1.2 for what actually happened.
The light stayed inside the water column and followed the curved path. He had
found a way to guide light!
The basic requirements still remain the same today — a light source and a clear
material (usually plastic or glass) for the light to shine through. The light can be
guided around any complex path as in Figure 1.3.
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Introduction to Fiber Optics
Figure 1.1
What was
expected to
happen
Figure 1.2
What actually
happened
Figure 1.3
Light can go
anywhere
Being able to guide light along a length of optic fiber has given rise to two
distinct areas of use, light guiding and communications.
Light guiding
There are many applications of light guiding — and more are being devised
every day.
Here are a few interesting examples.
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