Wavelength Division Multiplexing E-Book

Klaus Grobe

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Serie: Wiley Series in Pure and Applied Optics
• Sprache: Englisch

Seitenzahl: 651

Veröffentlichungsjahr: 2013

Beschreibung

In this book, Optical Wavelength Division Multiplexing (WDM) is approached from a strictly practical and application-oriented point of view. Based on the characteristics and constraints of modern fiber-optic components, transport systems and fibers, the text provides relevant rules of thumb and practical hints for technology selection, WDM system and link dimensioning, and also for network-related aspects such as wavelength assignment and resilience mechanisms. Actual 10/40 Gb/s WDM systems are considered, and a preview of the upcoming 100 Gb/s systems and technologies for even higher bit rates is given as well. Key features: * Considers WDM from ULH backbone (big picture view) down to PON access (micro view). * Includes all major telecom and datacom applications. * Provides the relevant background for state-of-the-art and next-gen systems. * Offers practical guidelines for system / link engineering.

Leseprobe

Contents

Cover

Wiley Series in Pure and Applied Optics

Title Page

Copyright

Acknowledgments

Chapter 1: Introduction to WDM

1.1 WDM Theory

1.2 History of WDM

References

Chapter 2: Optical Fiber Effects

2.1 Linear Effects

2.2 Nonlinear Fiber Effects

References

Chapter 3: Components and Subsystems

3.1 Transmitters

3.2 Transmission Line

3.3 Receivers

3.4 Digital Electronics

References

Chapter 4: Nonfiber-Related Effects

4.1 Linear Cross Talk

4.2 Noise in Optical Transmission Systems

References

Chapter 5: Modulation Formats for WDM

5.1 Basic Modulation

5.2 Pulse Shaping

5.3 Modulation Formats

5.4 Coherent Intradyne Dual-Polarization QAM Detection

5.5 Optical OFDM

5.6 Comparison of Modulation Formats

References

Chapter 6: System Realization

6.1 Access Networks

6.2 Corporate Networks (Storage Reach Extensions)

6.3 WDM Transport Encryption

6.4 Metro And Regional Networks

6.5 Long-Haul and Ultralong-Haul Systems

6.6 Future Network Configurations and Convergence

References

Chapter 7: WDM Network Management

7.1 Layered Network

7.2 Management Approaches

7.3 Basic EMS, NMS, and OSS Functionality

7.4 Data Communications Network

7.5 Management System Interfaces

7.6 Control Plane

References

Chapter 8: Selected Network Issues

8.1 Overview of the Optical Transport Network

8.2 Monitoring in WDM Systems

8.3 Flexible WDM Networks

8.4 Protection and Restoration

References

Chapter 9: Standards Relevant for WDM

9.1 ITU-T Recommendations

9.2 Others

Chapter 10: Practical Approximations and Tips

10.1 Conversion Between Bit Error Rate and Equivalent Q-Factor

10.2 Properties of a PRBS Signal

10.3 Chromatic Dispersion Values and Propagation Constants

References

Index

Wiley Series in Pure and Applied Optics

Founded by Stanley S. Ballard, University of Florida

EDITOR: Glenn Boreman, University of North Carolina at Charlotte

A complete list of the titles in this series appears at the end of this volume.

Copyright © 2014 by John Wiley & Sons, Inc. All rights reserved

Published by John Wiley & Sons, Inc., Hoboken, New Jersey

Published simultaneously in Canada

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Library of Congress Cataloging-in-Publication Data:

Grobe, Klaus.

Wavelength division multiplexing : a practical engineering guide / Klaus Grobe, Michael Eiselt. – 1st edition.

pages cm. – (Wiley-OSA series on optical communication ; 1)

Includes index.

ISBN 978-0-470-62302-2 (hardback)

1. Wavelength division multiplexing. I. Eiselt, Michael. II. Title.

TK5103.592.W38G76 2013

621.382′16–dc23

2013017946

Acknowledgments

Klaus Grobe wants to thank Hans-Peter Kuchenbecker and Casimer DeCusatis for their support that, directly and indirectly, led to this book. Special thanks also go to his father, Helmut, and his daughter, Kira.

Michael Eiselt wants to thank his managers and mentors Tingye Li, Hans-Georg Weber, Robert W. Tkach, and Robert M. Jopson for their support and guidance throughout his career. He also thanks his wife Renate and his daughters Susanna and Elisabeth for giving him encouragement and strength in his life.

The authors also want to acknowledge the support of their colleagues from ADVA. An extra thank-you goes to Marcus Sauter for the photographies. Finally, we thank the people at John Wiley & Sons, Inc. who supported this book, in particular Kari.

1

Introduction to WDM

1.1 WDM Theory

Wavelength division multiplexing (WDM) refers to a multiplexing and transmission scheme in optical telecommunications fibers where different wavelengths, typically emitted by several lasers, are modulated independently (i.e., they carry independent information from the transmitters to the receivers). These wavelengths are then multiplexed in the transmitter by means of passive WDM filters, and likewise they are separated or demultiplexed in the receiver by means of the same filters or coherent detection that usually involves a tunable local oscillator (laser).

WDM is an efficient means for increasing the transport capacity, or usable bandwidth, particularly of optical single-mode fibers. It also allows the separation of different customers' traffic in the wavelength (or optical frequency) domain and as such can be used as a multiple-access mechanism. The respective scheme is called wavelength-division multiple access (WDMA).

Modulated and multiplexed signals must be separated from each other or demultiplexed in order to be demodulated (otherwise, cross talk may appear). For separation, each pair of the respective signals must support orthogonality. For any two signals to be orthogonal, their scalar product must be zero:

(1.1)

(f, g*) is the scalar product of complex functions, where * denotes complex conjugation. (Equation 1.1) is also written for vector functions in order to be able to consider effects of orthogonally polarized signals.

The vanishing scalar product of the two signals is equivalent to a vanishing cross-correlation product or cross-correlation function (CCF). For the CCF, meaningful integration bounds must be considered, for example, integration over one symbol period. For optical WDM, the requirement (1.1) is easily fulfilled. Given that the different wavelength channels, including the Fourier transform-induced broadening due to the modulation, are properly spaced in the wavelength domain, any two different passbands of the WDM multiplexing (MUX) and demultiplexing (DMX) filters are orthogonal with respect to each other. In reality, (Eq. 1.1) may not be achieved exactly, but only approximately due to linear or nonlinear cross talk.

WDM is the generalization of frequency-domain multiplexing that is long known from radio and coaxial transmissions. With a WDM channel, it can be combined with any other of the known electrical multiplexing or multiple-access schemes. These include electrical frequency-domain multiplexing, which is then referred to as subcarrier multiplexing (SCM), time-domain multiplexing (TDM), and code-domain multiplexing. One scheme of particular interest for both the multiplexing and multiple access is orthogonal frequency-domain multiplexing (OFDM), which can be applied within a wavelength channel or covering the optical frequencies of several wavelength channels. The respective multiple access schemes are time-domain multiple access (TDMA), subcarrier multiple access (SCMA), frequency-domain multiple access (FDMA), and code-domain multiple access (CDMA).

1.2 History of WDM

The development toward commercial WDM transport systems as the common basis of all metropolitan area, regional, national, and international telecommunications networks was enabled by a number of relevant milestones:

1960: first laser developed [1]1966: first description of dielectric waveguides as a potential means for data transmission by Kao and Hockham [2]1970: first low-loss optical fiber produced (∼20 dB/km) [3,4]1976: first InGaAsP diode laser for 1300 nm window produced [5]1978: first low-loss single-mode fiber produced (∼0.2 dB/km) [6]1978: first experimental WDM systems developed [7]1987: first Erbium-doped fiber amplifier (EDFA) developed [8,9]1995: first commercial WDM systems available

These milestones were accompanied by the development of ever-improved components (e.g., diode lasers for the 1550 nm window) and various types of single-mode fibers.

High-speed single-mode fiber transmission started in 1981 with single-channel transmission at ∼1300 nm. Reasons were the availability of suitable semiconductor diode lasers and the fact that the first single-mode fibers [which are meanwhile referred to as standard single-mode fibers (SSMF)] had their region of lowest chromatic dispersion (CD) around 1300 nm. CD was the strongest deteriorating effect for early fiber transmission, limiting maximum reach. In addition, the region around 1300 nm had lowest fiber attenuation for wavelengths lower than the water-peak absorption region. The next step—for single-channel transmission—was to align the regions of lowest CD and lowest fiber attenuation in order to further maximize reach, in particular for the upcoming 10 Gb/s transmission. Since fiber attenuation is basically a material characteristic that cannot be influenced significantly for silica fibers, the region of lowest CD had to be shifted to ∼1550 nm in order to align both parameters. CD can be shifted since it depends on both the material and waveguide (geometry) characteristics. Hence, it can be shifted by designing a suitable radial refractive index profile. This has been done around 1990, and the result is the so-called dispersion-shifted fiber (DSF)—sometimes also referred to as dispersion-shifted single-mode (DSSM) fiber. DSF was heavily deployed in Japan and certain other regions (e.g., parts of the United States and Spain).

The deployment of DSF badly interfered with the usage of first WDM systems. The problem was caused by transmitting several WDM channels around 1550 nm, at close-to-zero CD. The EDFA, which had meanwhile been invented and which revolutionized long-reach fiber transmission, enabled long transparent link lengths exceeding 600 km. With increasing transparent link lengths and increasing total and per-channel fiber launch power, a fiber characteristic—nonlinearity—got relevant that had not been considered seriously before. Though basic work on fiber nonlinearity had been published in the 1970s (see Section 2.2), one of the nonlinear effects, four-wave mixing (FWM), now started to seriously limit WDM transmission on real-world fibers. FWM is the parametric mixing effect that occurs due to the fundamental fiber's cubic Kerr nonlinearity. As with all parametric mixing, it relies on phase matching between the mixing waves that can be achieved in real fiber in the absence of CD. This was just the design goal for single-channel transmission DSFs. Once it efficiently occurs, FWM cannot be counteracted anymore; it thus fundamentally limits reach.

The problem with WDM transmission on fibers with close-to-zero CD then led to the development of a family of modified single-mode fibers. These fiber designs, known as nonzero dispersion-shifted fibers (NZ-DSF) or dispersion-flattened single-mode (DFSM) fibers, followed the idea to provide nonzero CD that is yet smaller than that in SSMF in order to reduce both the linear and nonlinear distortions. The second-generation WDM systems could achieve approximately the same maximum reach (which was still limited in the 600 km range) on SSMF and NZ-DSF. With transparent reach extended into the ultralong-haul domain and the techniques for optical CD compensation having been developed during the 1990s, it turned out that nonlinear distortions were still the dominating reach limitation. This led to the development of several NZ-DSF with increased (and also flattened) CD. Finally, with the product of transparent reach and total capacity (in terms of number of WDM channels and per-channel bit rate) further increasing, it turned out that in the presence of nonlinearity, SSMF with their high CD are the optimum choice of silica fibers. Further improvements of the bandwidth-reach product will likely require disruptive new fiber types.

Driven by improvements of components and modulation and equalization techniques, the total transport capacity of WDM systems has largely increased since the first experiments with WDM. This is shown in Fig. 1.1 for both the experimental and commercial WDM systems.

Figure 1.1 Development of WDM systems transport capacity over time.

Two aspects can be derived from Fig. 1.1. First, commercial WDM systems are following “hero” experiments somewhat more timely now and both are approaching an area of slowed down capacity improvement. Over the next few years, WDM on SSMF will finally reach what is now known as the nonlinear Shannon limit [10]. Further progress beyond this limit will require new fiber types.

References

1. T.H. Maiman, Stimulated optical radiation in ruby, Nature, Vol. 187, No. 4736, 1960, pp. 493–494.

2. K.C. Kao and G.A. Hockham, Dielectric-fibre surface waveguide for optical frequencies, Proc. IEEE, Vol. 113, No. 7, 1966, pp. 1151ff.

3. D.B. Keck et al., On the ultimate lower limit of attenuation in glass optical waveguides, Appl. Phys. Lett., Vol. 22, No. 7, April 1973, pp. 307ff.

4. P.C. Schultz Making the first low loss optical fibers for communications, ECOC2010 Torino, September 2010.

5. J. Hsieh et al., Room-temperature cw operation of GaInAsP/InP double-heterostructure diode lasers emitting at 1.1 μm, Appl. Phys. Lett., Vol. 28, No. 12, 1976, pp. 709–711.

6. H. Murata and N. Inagaki, Low-loss single-mode fiber development and splicing research in Japan, IEEE J. Quantum Electron. Vol. 17, No. 6, June 1981, pp. 835–849.

7. W.J. Tomlinson and C. Lin, Optical wavelength-division multiplexer for the 1–1.4-micron spectral region, Electron. Lett., Vol. 14, May 1978, pp. 345–347.

8. R.J. Mears et al., Low-threshold tunable CW and Q-switched fiber laser operating at 1.55 μm, Electron. Lett., 22, 1986, pp. 159–160.

9. R.J. Mears et al., Low-noise erbium-doped fiber amplifier at 1.54 μm, Electron. Lett., Vol. 23, 1987, pp. 1026–1028.

10. R.-J. Essiambre et al., Capacity limits of optical fiber networks, IEEE J. Lightwave Technol., Vol. 28, No. 4, 2010, pp. 662–701.