Free-Space Optics: Enabling Optical Connectivity in Today’S Networks
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Free-Space Optics: Enabling Optical Connectivity in Today’s Networks Heinz Willebrand, Ph.D., and Baksheesh S. Ghuman 800 East 96th St.,Indianapolis,Indiana 46240 USA ASSOCIATE PUBLISHER Free-Space Optics: Enabling Linda Engelman Optical Connectivity in Today’s ACQUISITIONS EDITOR Networks Dayna Isley DEVELOPMENT EDITOR Copyright © 2002 by Sams Publishing Laurie McGuire All rights reserved. No part of this book shall be reproduced, stored in a retrieval system, or transmitted by any means, electronic, mechanical, photo- MANAGING EDITOR copying, recording, or otherwise, without written permission from the pub- Charlotte Clapp lisher. No patent liability is assumed with respect to the use of the information PROJECT EDITOR contained herein. Although every precaution has been taken in the preparation Carol Bowers of this book, the publisher and author assume no responsibility for errors or omissions. Nor is any liability assumed for damages resulting from the use of COPY EDITOR the information contained herein. Karen A. Gill International Standard Book Number: 0-672-32248-x INDEXER Tim Tate Library of Congress Catalog Card Number: 2001089233 Printed in the United States of America PROOFREADER Jessica McCarty First Printing: December 2001 TECHNICAL EDITORS 04 03 02 01 4 3 2 1 Peter Schoon Trademarks David Lively All terms mentioned in this book that are known to be trademarks or service TEAM COORDINATOR marks have been appropriately capitalized. Sams Publishing cannot attest to Lynne Williams the accuracy of this information. Use of a term in this book should not be INTERIOR DESIGNER regarded as affecting the validity of any trademark or service mark. Gary Adair COVER DESIGNER Warning and Disclaimer Gary Adair Every effort has been made to make this book as complete and as accurate as possible, but no warranty or fitness is implied. The information provided is on PAGE LAYOUT an “as is” basis. The authors and the publisher shall have neither liability nor Octal Publishing, Inc. responsibility to any person or entity with respect to any loss or damages aris- ing from the information contained in this book or from the use of the pro- grams accompanying it. Contents at a Glance Preface xi 1 Introduction to Free-Space Optics 1 2 Fundamentals of FSO Technology 9 3 Factors Affecting FSO 47 4 Integration of FSO in Optical Networks 65 5 The FSO Market 101 6 Installation of Free-Space Optical Systems 123 7 Free-Space Optics and Laser Safety 137 8 Service Provider Issues 149 9 Alternative Access Technologies 163 10 The Outlook for FSO 207 A Frequently Asked Questions 217 B Laser Safety Resources 223 Glossary 227 Index 241 Table of Contents Preface xi 1 Introduction to Free-Space Optics 1 Alternative Bandwidth Technologies ......................................................2 Fiber Versus FSO ....................................................................................3 Fiber-Optic Cable ..............................................................................4 Environmental Challenges to Transmission Through the Air ............................................................................5 Other Points of Comparison ..............................................................6 The Role of FSO in the Network ..........................................................6 Summary ................................................................................................7 Sources ....................................................................................................7 2 Fundamentals of FSO Technology 9 How FSO Works: An Overview ..........................................................10 Transmitters ..........................................................................................12 Light-Emitting Diodes (LED) ........................................................12 Laser Principles ..............................................................................14 Laser Diodes ....................................................................................19 Receivers ..............................................................................................26 Principles of Light Detection ..........................................................27 Semiconductor Photodiode ..............................................................28 PIN Diodes ......................................................................................28 Avalanche Photodiodes (APD) ........................................................29 Receiver Selection Criteria for FSO ................................................31 Optical Subsystems ..............................................................................32 Classical Ray Lens Optics ..............................................................32 Optical Designs for Free-Space Optics ..........................................35 Tracking and Acquisition ......................................................................35 Wide Beam Transmission Systems ................................................36 Auto Tracking ..................................................................................36 Gimbals ............................................................................................37 Servo-Based Tracking Systems ......................................................38 Steering Mirror-Tracking Designs ..................................................38 Micro-Electromechanical Systems (MEMS) ..................................38 Quad Detectors ................................................................................39 CCD Arrays ....................................................................................40 Link Margin Analysis ..........................................................................40 Optical Loss ....................................................................................42 Geometrical Loss ............................................................................43 vi FREE-SPACE OPTICS: ENABLING OPTICAL CONNECTIVITY IN TODAY’S NETWORKS Pointing Loss ..................................................................................44 Atmospheric Loss and Receiver Sensitivity ....................................45 Simple Link Analysis Tool ..............................................................46 Summary ..............................................................................................46 3 Factors Affecting FSO 47 Transmission of IR Signals Through the Atmosphere ........................48 Beer’s Law ......................................................................................48 Scattering ........................................................................................49 Absorption ......................................................................................51 Turbulence ......................................................................................53 The Impact of Weather ........................................................................56 Rain ..................................................................................................57 Snow ................................................................................................57 Fog ..................................................................................................57 Line of Sight (LOS) ..............................................................................59 Determining LOS ............................................................................59 Other Factors Affecting FSO ................................................................60 Visibility ..........................................................................................60 Distance ..........................................................................................60 Bandwidth ........................................................................................61 Selecting the Transmission Wavelength ..............................................61 Summary ..............................................................................................62 Sources ..................................................................................................63 4 Integration of FSO in Optical Networks 65 The Optical Networking Revolution ..................................................66 Benefits of Next-Generation Optical Networking ................................68 The Recent Past: SONET/SDH ......................................................69 First-Generation Limitations ..........................................................70 The Second-Generation Revolution ................................................71 Classifying the Global Optical Network ..............................................77 Long-Haul Optical Networking ......................................................79 Metropolitan Area Networks ..........................................................80 Access Networks ............................................................................83 Driving FSO from the Edge ................................................................90 VPN Services ..................................................................................91 Broadband Internet Access ..............................................................91 Transparent LAN Services ..............................................................92 Optical Access at Multitenant Buildings ........................................92 Private Line Services ......................................................................93