NBS A111D3 PUBLICATIONS NBS SPECIAL PUBLICATION 637 Volume 2 U.S. DEPARTMENT OF COMMERCE/National Bureau of Standards Optical Fiber Characterization 130 .U57 No. 637 Vol, 2 1933 c ^ NATIONAL BUREAU OF STANDARDS The National Bureau of Standards' was established by an act of Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis tor equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and the Institute for Computer Sciences and Technology. THE NATIONAL MEASUREMENT LABORATORY provides the national system of physical and chemical and materials measurement; coordinates the system with measurement systems of other nations and furnishes essential services leading to accurate and uniform physical and chemical measurement throughout the Nation's scientific community, industry, and commerce; conducts materials research leading to improved methods of measurement, standards, and data on the properties of materials needed by industry, commerce, educational institutions, and Government; provides advisory and research services to other Government agencies; develops, produces, and distributes Standard Reference Materials; and provides calibration services. The Laboratory consists of the following centers: Absolute Physical Quantities 2 — Radiation Research — Chemical Physics — Analytical Chemistry — Materials Science THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement capabilities; provides engineering measurement traceability services; develops test methods and proposes engineering standards and code changes; develops and proposes new engineering practices; and develops and improves mechanisms to transfer results of its research to the ultimate user. The Laboratory consists of the following centers: Applied Mathematics — Electronics and Electrical Engineering 2 — Manufacturing Engineering — Building Technology — Fire Research — Chemical Engineering 2 THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and provides scientific and technical services to aid Federal agencies in the selection, acquisition, application, and use of computer technology to improve effectiveness and economy in Government operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing the Federal Information Processing Standards Program, developing Federal ADP standards guidelines, and managing Federal participation in ADP voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and provides the technical foundation for computer-related policies of the Federal Government. The Institute consists of the following centers: Programming Science and Technology — Computer Systems Engineering. 'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Washington, DC 20234. ! Some divisions within the center are located at Boulder, CO 80303. Optical Fiber Characterization Attenuation, Frequency Domain Bandwidth, and Radiation Patterns G.E. Chamberlain G.W. Day D.L. Franzen R.L Gallawa E.M. Kim I M. Young Electromagnetic Technology Division Center for Electronics and Electrical Engineering National Bureau of Standards Boulder, CO 80303 Second of a series on optical fiber technology. U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director Issued October 1983 Library of Congress Catalog Card Number: 82-600563 National Bureau of Standards Special Publication 637 Volume 2 Natl. Bur. Stand. (U.S.), Spec. Publ. 637, Vol. 2, 239 pages (Oct. 1983) CODEN: XNBSAV U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1983 CONTENTS Page Chapter 1. Measurement of Multimode Optical Fiber Attenuation R. L. Gallawa, G. E. Chamberlain, G. W. Day, D. L. Franzen, and M. Young 1 Chapter 2. Measurement of Optical Fiber Bandwidth in the Frequency Domain G. W. Day 57 Chapter 3. Measurement of Near-Field Radiation Patterns from Optical Fibers E. M. Kim and D. L. Franzen 101 Chapter 4. Measurement of Far-Field Radiation Patterns from Optical Fibers E. M. Kim and D. L. Franzen 187 Appendix: Optical Waveguide Communications Glossary 207 PREFACE During the past several years, a number of optical fiber measurement systems have been developed at the National Bureau of Standards. This book is the second volume of a series intended to describe the design and performance of these systems. Volume 1 includes a description of systems to measure backscatter, bandwidth (time domain), and index profile (refracted near field); Volume 2 covers attenuation, bandwidth (frequency domain), and radiation patterns. Chapters describing these systems are minor revisions of former NBS Technical Notes, many of which are now out of print. Each chapter contains a brief tutorial on the particular subject and a detailed description of the system. This level of engineering detail is not usually found in other books on the subject. The appendix of this volume contains a glossary of optical fiber terms and is a reprint of NBS Handbook 140 (1982) which is now out of print. The following individuals were contributors to that handbook: A. G. Hanson, L. R. Bloom, A. H. Cherin, G. W. Day, R. L. Gallawa, E. M. Gray, C. Kao, F. P. Kapron, B. S. Kawasaki, P. Reitz, and M. Young. The reader should be cautioned that terminology continually evolves and this glossary will undoubtedly undergo change as new terms are added and others revised. However, the glossary does represent a several -year effort by many in the industry and is currently the best avai lable. The authors would like to thank M. E. DeWeese for preparing the manuscript and providing editorial assistance. Partial support for the work reported here was provided by the Department of Defense, Calibration Coordination Group (CCG). Boulder, Colorado 1983 v ABSTRACT This is the second volume of a series intended to describe optical fiber measurement systems developed at the National Bureau of Standards. The topics covered in this volume are attenuation, bandwidth (frequency domain), and far-field near-field radiation patterns. Each chapter includes a tutorial section and a detailed description of the apparatus. The volume concludes with a glossary of optical communications terms. Key words: attenuation; bandwidth; core diameter; far field; measurements; near field; optical fiber. vi Chapter 1 Measurement of Multimode Optical Fiber Attenuation R. L. Gallawa G. E. Chamberlain G. W. Day D. L. Franzen M. Young This document is one of a series which describes optical fiber measurement capabilities at the National Bureau of Standards. We concentrate here on the measurement of attenuation of multimode, telecommunication-grade fibers for the wavelength range of 850 nm to 1300 nm. The document begins by discussing the need for restricted launch conditions, the most fundamental and crucial aspect of precise attenuation measurements. The limited phase space launch (also called the beam optics launch) and the mode filter launch are discussed. Attention then turns to the practical matter of ensuring that the conditions of the restricted launch are met. Discussions of system noise and system linearity are also included. The document describes measurement procedure and results obtained in the laboratory using three typical fibers. Results are presented for the two wavelengths of current interest: 850 nm and 1300 nm. The procedures are applicable to any wavelength, however. The document touches briefly on the matter of monomode fibers. Finally, a summary of the results from an interlaboratory comparison are presented to give perspective to the stability of a fiber subjected to handling and shipping. 1 CONTENTS Page 1. INTRODUCTION 3 2. LAUNCH CONDITIONS . 7 2.1 Phase Space 8 2.1.1 A Summary of Phase Space Concepts 18 2.2 LPS Launch 20 2.3 Mode Filter Launch 22 3. COMPONENT AND SYSTEM VARIABILITIES 26 3.1 Spot Size and Launch Numerical Aperture 27 3.2 Mode Filter Qualification 34 3.3 Component Linearity 37 3.4 System Linearity 37 3.5 System Noise 38 3.6 Detector Uniformity 39 3.7 Measurement Procedure 40 3.8 Some Results 44 4. MEASUREMENT COMPARISONS AND RESULTS 44 4.1 Participants and Instructions 44 4.2 Comparison Results 46 4.3 Attenuation Measurements in High-DMA Fibers 50 4.4 Summary of Interlaboratory Comparisons 52 5. REFERENCES 53 APPENDIX A. MODE VOLUME AND LIMITED PHASE SPACE 55 2 1. INTRODUCTION Two operational parameters are basic to the utility of any transmission line: attenua- tion and bandwidth. These two determine repeater spacing and ultimate cost of a telecom- munication network. Both must be characterized because either attenuation or bandwidth may limit the range-bandwidth product of a communication link; the