Fluoride Glass Optical Fibres

276 Pages·1990·7.189 MB·English

by  P. W. France, M. G. Drexhage, J. M. Parker, M. W. Moore, S. F. Carter, J. V. Wright (auth.)

Fluoride Glass Optical Fibres
Fluoride Glass Optical Fibres
by
P.W. FRANCE
British Telecom Research Laboratories
Ipswich, UK
with co-authors
M.G. DREXHAGE
Galileo Electro-Optics Corporation
Massachussetts, USA
J.M. PARKER
School of Materials
University of Sheffield, UK
M.W. MOORE
S.F. CARTER
and
J.V. WRIGHT
British Telecom Research Laboratories
Ipswich, UK
Blackie
Glasgow and London
Published in the USA and Canada by
CRC Press, Inc.
Boca Raton, Florida
Blackie and Son Ltd
Bishopbriggs, Glasgow G64 2NZ
and
7 Leicester Place, London WC2H 7BP
Published in the USA and Canada by
CRC Press, Inc.
2000 Corporate Blvd, N.W., Boca Raton, FL 33431
CD 1990 Blackie and Son Ltd
First published 1990
Softcover reprint of the hardcover 1st edition 1990
All rights reserved
No part of this publication may be reproduced, stored in a retrieval system,
or transmitted, in any form or by any means-graphic,
electronic or mechanical, including photocopying,
recording, taping-without the written permission of the Publishers
British Library Cataloguing in Publication Data
France, p, W.
Fluoride glass optical fibres.
\. Infrared fibre optics
l. Title
621.36'92
ISBN-13: 978-94-011-6867-0
Library of Congress Cataloging-in-Publication Data
Fluoride glass optical fibres/edited by P.W. France.
p. cm.
ISBN-13: 978-94-011-6867-0 e-ISBN-13: 978-94-011-6865-6
DOl: 10.1007/978-94-011-6865-6
I. Optical fibres, 2. Infrared technology, I. France. P,W.
TAI800.F57 1989 89-22246
621.36' 92 -dc20 CIP
Phototypesetting by Thomson Press (India) Limited, New Delhi
Preface
One of the most exciting prospects for optical fibres made from fluoride glasses
is the possibility of providing long distance optical communication systems
without the need for repeaters. This objective has stimulated much of the work
into fluoride glasses over the past ten years, and has prompted the writing of
this book. It has also emerged that fluoride fibres can transmit both visible and
infrared energy (from about 0.5 to 5 ,urn) and that they have many applications
outside the field of telecommunications. These include optical fibre sensors
(particularly in remote infrared spectroscopy), laser surgery and fibre lasers.
Several companies are now established in the field, and good quality fluoride
fibres are available from sources throughout the USA, Europe and Japan.
Moreover, the first commercial instruments based on fluoride fibres are
finding their way to the market place and these fibres will undoubtedly form
the basis of many more instruments yet to be developed.
The work presented in this book represents the field both from an academic
understanding of the materials and ways to convert them into fibre, and from a
practical and commercial viewpoint. The principal author and some of the co
authors are based at the British Telecom Research Laboratories in the UK.
These authors have been able to follow the technology from basic research to
manufacture and are aware ofthe many non-telecom applications. Many close
and personal links have been established with universities and industry and
these are represented by the contributions from Dr John Parker of the
University of Sheffield and Dr Martin Drexhage ofthe Galileo Electro-Optics
Corporation. Dr Drexhage has been a leading pioneer of the field within the
USA and is now overseeing the development of the technology into
manufacturing.
Chapter 1 presents an overview and provides a historical summary of the
development ofthe field. Chapter 2 describes the general properties of fluoride
glasses, both physical and optical, and is a useful reference chapter. Chapter 3
discusses the propagation of power in optical fibres, placing particular
emphasis on longer wavelengths. This leads on to a detailed discussion of
manufacturing techniques for fluoride glasses and ways to convert them into
fibre in Chapter 4. Chapters 5,6 and 7 discuss the optical losses in fibre, both
intrinsic and extrinsic, and Chapter 8 presents the most up to date information
on measured losses and measurement techniques. Chapter 9 presents data on
mechanical properties, strength and durability. Finally, Chapter 10 discusses
applications of fluoride fibres, including long wavelength communications
systems, fibre lasers and amplifiers, laser surgery, and infrared fibre sensors.
VI PREFACE
The book is aimed at anyone working in the field of optical fibres made from
fluoride glasses, from academic researchers to engineers attempting to devise
instruments based on the fibres, and will be of interest to scientists and
engineers who are curious to hear of developments in a new and exciting field.
The authors would like to acknowledge their respective establishments for
support and advice whilst writing this book, and wish to acknowledge the
whole community of scientists and engineers who have helped to advance the
field and to whom many references have been made throughout the book.
P.W.F.
Authors
S.F. Carter British Telecom Research Laboratories
Martlesham Heath
Ipswich IPS 7RE, UK
M.G. Drexhage Galileo Electro-Optics Corporation
Galileo Park
PO Box 550
Sturbridge
MA 01566
USA
P.W. France British Telecom Research Laboratories
Martlesham Heath
Ipswich IPS 7RE, UK
M.W. Moore British Telecom Research Laboratories
Martlesham Heath
Ipswich IPS 7RE, UK
J.M. Parker School of Materials
University of Sheffield
Elmficld
Northumberland Road
Sheffield S 10 2TZ, UK
J.V. Wright British Telecom Research Laboratories
Martlesham Heath
Ipswich IPS 7RE, UK.
Contents
1 Perspective and overview 1
M.G. DREXHAGE
1.1 IntroductIon
1.2 OptIcal fihre fundamentals 2
1.3 Loss mechanisms in optical fibre materials 4
1.3.1 Power losses and UnIts 4
I 32 Extnnslc and intrinsic loss mechanisms 5
1.3.3 Intnnslc transparency: mechanIsms and models 6
14 Long wavelength fibre materials 9
1.4.1 Materials. choices and sources of InformatIOn 9
14.2 Silica-based fibres 11
1.43 Crystalline fibre materials 13
1.4.4 ChalcogenIde glasses 15
1.4.5 Hollow Infrared waveguIdes 16
1.5 Fluonde glasses and optical fibres 16
1.5.1 Concepts. definitions and materials 16
1.5.2 Fluonde fibre technology: a brief personal history 20
1.6 ApplIcatIons for Infrared optIcal fibres 25
1.7 Future prospects 27
References 29
2 Properties of fluoride glasses 32
1.M. PARKER and P.W. FRANCE
2.1 IntroductIOn 32
2.2 Glass-forming systems. structure and crystallization 32
2.2.1 Structural models 32
2.2.2 Crystallization behaVIOur 36
2.3 Thermal propertIes 42
2.3.1 Viscosity 42
2.3.2 Thermal expansIOn behaviour 45
2.3.3 Diffusion 48
2.3.4 Thermal conductivity 48
2.3.51 Heat transfer 49
2.4 Other properties 51
2.4.1 Density 51
2.4.2 Gas solubility 52
2.4.3 Elastic moduli 53
2.4.4 Microhardness 54
2.5 Optical properties 54
2.5.1 Infrared absorption 54
2.5.2 Ultraviolet absorptIOn 61
2.5.3 Intrinsic scattering loss 62
2.5.4 Minimum intrinsic losses 64
2.5.5 Refractive index and dIspersion 66
2.5.6 Fluorescence 69
References 70
X CONTENTS
3 Propagation in optical fibres 75
J.V. WRIGHT
3.1 Introduction 75
3.2 Multimode fibres 76
3.2.1 Propagation in multi mode fibres 76
3.2.2 Attenuation 83
3.2.3 Real fibres and fibre links 83
3.3 Monomode fibres 85
3.3.1 Propagation in monomode fibres 85
3.3.2 Optimized fibre design 94
3.3.3 Non-linear elTects 97
References 98
4 Manufacture of infrared fibres 100
P.W. FRANCE
4.1 Materials preparation 100
4.1.1 Introduction 100
4.1.2 Synthetic routes 101
4.1.3 Purification 103
4.2 Melting techniques 105
4.2.1 Melting environments 105
4.2.2 Containment vessels 105
4.2.3 Reactive atmosphere processing 106
4.2.4 Homogenization and fining 107
4.2.5 Crystallization 107
4.3 Fibre fabrication 108
4.3.1 Glass compositions 108
4.3.2 Glass melting 109
4.3.3 Preform fabrication 113
4.3.4 Fibre drawing 114
4.3.5 Other techniques 116
4.3.6 Monomode fibre 117
4.4 Problems 118
4.5 Fibre results 120
References 121
5 Intrinsic loss measurements 122
P.W. FRANCE
5.1 Introduction 122
5.2 Rayleigh scattering 122
5.3 IR multi phonon edge 124
5.4 Minimum intrinsic loss 126
5.5 Longer wavelength transmitting fibres 127
References 130
6 Extrinsic absorption 132
P.W. FRANCE
6.1 Introduction 132
6.2 Spectrometer measurements 133
6.2.1 Nomenclature 133
6.2.2 Experimental 134
CONTENTS XI
6.3 Absorption due to water 136
6.3.1 OH - in oxide glasses 136
6.3.2 OH - in fluoride glasses 138
6.3.3 OH - in ZrF4 IR fibres 140
6.4 Absorption due to transition metal ions 143
6.4.1 Introduction 143
6.4.2 Oxidation-reduction equilibrium 144
6.4.3 Ligand field theory 145
6.4.4 Absorption spectra 147
6.4.5 Discussion 157
6.5 Absorption due to rare earth ions 159
6.5.1 Introduction 159
6.5.2 Oxidation states 159
6.5.3 Electronic spectra 160
6.5.4 Absorption spectra 162
6.5.5 Discussion 179
6.6 Other impurities 184
6.6.1 Dissolved gases 184
6.6.2 Molecular ions 182
6.6.3 Reduced species 182
6.6.4 Oxide absorption 182
References 184
7 Extrinsic scattering 186
P.W. FRANCE
7.1 Introduction 186
7.2 Identification of scattering centres 187
7.2.1 Large crystals 187
7.2.2 Gas bubbles 187
7.2.3 Sub-micron centres 188
7.2.4 Deviations of fibre geometry 188
7.3 Scattering theory 188
7.4 Scattering solutions for limiting cases 189
7.4.1 Small spheres, intermediate index (Rayleigh scattering) 189
7.4.2 Small high index spheres 190
7.4.3 Intermediate size spheres with m close to 1 (Rayleigh-Gans) 191
7.4.4 Intermediate size sphere with higher refractive index 191
7.4.5 High index (conducting) spheres of small size 193
7.4.6 High index spheres of intermediate size 194
7.4.7 Large spheres with index close to 1 194
7.4.8 Large spheres with high refractive index 194
7.5 Solutions for metallic (absorbing) spheres 195
7.6 Applications to practical examples 197
7.7 Calculations of scattering loss 199
7.8 Scattering loss in fibres 202
7.9 Conclusions 203
References 204
8 Measured losses in fibres 205
M.W. MOORE
8.1 Introduction 205
8.2 Available techniques 206
6.2.1 Sources and detectors 206
8.2.2 Totalloss 207
8.2.3 Absorption 207
8.2.4 Scattering 208