Prelims 3/5/01 11:48 Page i Introduction to Fiber Optics Prelims 3/5/01 11:48 Page ii Prelims 3/5/01 11:48 Page iii Introduction to Fiber Optics 2nd Edition John Crisp OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI Prelims 3/5/01 11:48 Page iv 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 Prelims 3/5/01 11:48 Page v 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 Prelims 3/5/01 11:48 Page vi Contents 20 Some final thoughts 206 Glossary 210 Quiz time answers 217 Index 227 vi Prelims 3/5/01 11:48 Page vii 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 Prelims 3/5/01 11:48 Page viii ch01 3/5/01 11:48 Page 1 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. 1 ch01 3/5/01 11:48 Page 2 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. 2