Enabling Technologies for High Spectral-efficiency Coherent Optical Communication Networks: (Wiley Series in Microwave and Optical Engineering)

Enabling Technologies for High Spectral-efficiency Coherent Optical Communication Networks Presents the technological advancements that enable high spectral-efficiency and high-capacity fiber-optic communication systems and networks This book examines key technology advances in high spectral-efficiency fiber-optic communication systems and networks, enabled by the use of coherent detection and digital signal processing (DSP). The first of this book’s 16 chapters is a detailed introduction. Chapter 2 reviews the modulation formats, while Chapter 3 focuses on detection and error correction technologies for coherent optical communication systems. Chapters 4 and 5 are devoted to Nyquist-WDM and orthogonal frequency-division multiplexing (OFDM). In chapter 6, polarization and nonlinear impairments in coherent optical communication systems are discussed. The fiber nonlinear effects in a non-dispersion-managed system are covered in chapter 7. Chapter 8 describes linear impairment equalization and Chapter 9 discusses various nonlinear mitigation techniques. Signal synchronization is covered in Chapters 10 and 11. Chapter 12 describes the main constraints put on the DSP algorithms by the hardware structure. Chapter 13 addresses the fundamental concepts and recent progress of photonic integration. Optical performance monitoring and elastic optical network technology are the subjects of Chapters 14 and 15. Finally, Chapter 16 discusses spatial-division multiplexing and MIMO processing technology, a potential solution to solve the capacity limit of single-mode fibers. Contains basic theories and up-to-date technology advancements in each chapter Describes how capacity-approaching coding schemes based on low-density parity check (LDPC) and spatially coupled LDPC codes can be constructed by combining iterative demodulation and decoding Demonstrates that fiber nonlinearities can be accurately described by some analytical models, such as GN-EGN model Presents impairment equalization and mitigation techniques Enabling Technologies for High Spectral-efficiency Coherent Optical Communication Networks is a reference for researchers, engineers, and graduate students.

Table of Contents:
List of Contributors xv Preface xvii 1 Introduction 1 Xiang Zhou and Chongjin Xie 1.1 High-Capacity Fiber Transmission Technology Evolution, 1 1.2 Fundamentals of Coherent Transmission Technology, 4 1.2.1 Concept of Coherent Detection, 4 1.2.2 Digital Signal Processing, 5 1.2.3 Key Devices, 7 1.3 Outline of this Book, 8 References, 9 2 Multidimensional Optimized Optical Modulation Formats 13 Magnus Karlsson and Erik Agrell 2.1 Introduction, 13 2.2 Fundamentals of Digital Modulation, 15 2.2.1 System Models, 15 2.2.2 Channel Models, 17 2.2.3 Constellations and Their Performance Metrics, 18 2.3 Modulation Formats and Their Ideal Performance, 20 2.3.1 Format Optimizations and Comparisons, 21 2.3.2 Optimized Formats in Nonlinear Channels, 30 2.4 Combinations of Coding and Modulation, 31 2.4.1 Soft-Decision Decoding, 31 2.4.2 Hard-Decision Decoding, 37 2.4.3 Iterative Decoding, 39 2.5 Experimental Work, 40 2.5.1 Transmitter Realizations and Transmission Experiments, 40 2.5.2 Receiver Realizations and Digital Signal Processing, 45 2.5.3 Formats Overview, 49 2.5.4 Symbol Detection, 50 2.5.5 Realizing Dimensions, 51 2.6 Summary and Conclusions, 54 References, 56 3 Advances in Detection and Error Correction for Coherent Optical Communications: Regular, Irregular, and Spatially Coupled LDPC Code Designs 65 Laurent Schmalen, Stephan ten Brink, and Andreas Leven 3.1 Introduction, 65 3.2 Differential Coding for Optical Communications, 67 3.2.1 Higher-Order Modulation Formats, 67 3.2.2 The Phase-Slip Channel Model, 69 3.2.3 Differential Coding and Decoding, 71 3.2.4 Maximum a Posteriori Differential Decoding, 78 3.2.5 Achievable Rates of the Differentially Coded Phase-Slip Channel, 81 3.3 LDPC-Coded Differential Modulation, 83 3.3.1 Low-Density Parity-Check (LDPC) Codes, 85 3.3.2 Code Design for Iterative Differential Decoding, 91 3.3.3 Higher-Order Modulation Formats with V < Q, 100 3.4 Coded Differential Modulation with Spatially Coupled LDPC Codes, 101 3.4.1 Protograph-Based Spatially Coupled LDPC Codes, 102 3.4.2 Spatially Coupled LDPC Codes with Iterative Demodulation, 105 3.4.3 Windowed Differential Decoding of SC-LDPC Codes, 108 3.4.4 Design of Protograph-Based SC-LDPC Codes for Differential-Coded Modulation, 108 3.5 Conclusions, 112 Appendix: LDPC-Coded Differential Modulation—Decoding Algorithms, 112 Differential Decoding, 114 LDPC Decoding, 115 References, 117 4 Spectrally Efficient Multiplexing: Nyquist-WDM 123 Gabriella Bosco 4.1 Introduction, 123 4.2 Nyquist Signaling Schemes, 125 4.2.1 Ideal Nyquist-WDM (Δf = Rs), 126 4.2.2 Quasi-Nyquist-WDM (Δf > Rs), 128 4.2.3 Super-Nyquist-WDM (Δf < Rs), 130 4.3 Detection of a Nyquist-WDM Signal, 134 4.4 Practical Nyquist-WDM Transmitter Implementations, 137 4.4.1 Optical Nyquist-WDM, 139 4.4.2 Digital Nyquist-WDM, 141 4.5 Nyquist-WDM Transmission, 146 4.5.1 Optical Nyquist-WDM Transmission Experiments, 148 4.5.2 Digital Nyquist-WDM Transmission Experiments, 148 4.6 Conclusions, 149 References, 150 5 Spectrally Efficient Multiplexing – OFDM 157 An Li, Di Che, Qian Hu, Xi Chen, and William Shieh 5.1 OFDM Basics, 158 5.2 Coherent Optical OFDM (CO-OFDM), 161 5.2.1 Principle of CO-OFDM, 161 5.3 Direct-Detection Optical OFDM (DDO-OFDM), 169 5.3.1 Linearly Mapped DDO-OFDM, 169 5.3.2 Nonlinearly Mapped DDO-OFDM (NLM-DDO-OFDM), 173 5.4 Self-Coherent Optical OFDM, 174 5.4.1 Single-Ended Photodetector-Based SCOH, 175 5.4.2 Balanced Receiver-Based SCOH, 177 5.4.3 Stokes Vector Direct Detection, 177 5.5 Discrete Fourier Transform Spread OFDM System (DFT-S OFDM), 180 5.5.1 Principle of DFT-S OFDM, 180 5.5.2 Unique-Word-Assisted DFT-S OFDM (UW-DFT-S OFDM), 182 5.6 OFDM-Based Superchannel Transmissions, 183 5.6.1 No-Guard-Interval CO-OFDM (NGI-CO-OFDM) Superchannel, 184 5.6.2 Reduced-Guard-Interval CO-OFDM (RGI-CO-OFDM) Superchannel, 186 5.6.3 DFT-S OFDM Superchannel, 188 5.7 Summary, 193 References, 194 6 Polarization and Nonlinear Impairments in Fiber Communication Systems 201 Chongjin Xie 6.1 Introduction, 201 6.2 Polarization of Light, 202 6.3 PMD and PDL in Optical Communication Systems, 206 6.3.1 PMD, 206 6.3.2 PDL, 208 6.4 Modeling of Nonlinear Effects in Optical Fibers, 209 6.5 Coherent Optical Communication Systems and Signal Equalization, 211 6.5.1 Coherent Optical Communication Systems, 211 6.5.2 Signal Equalization, 213 6.6 PMD and PDL Impairments in Coherent Systems, 215 6.6.1 PMD Impairment, 216 6.6.2 PDL Impairment, 222 6.7 Nonlinear Impairments in Coherent Systems, 228 6.7.1 System Model, 229 6.7.2 Homogeneous PDM-QPSK System, 230 6.7.3 Hybrid PDM-QPSK and 10-Gb/s OOK System, 233 6.7.4 Homogeneous PDM-16QAM System, 234 6.8 Summary, 240 References, 241 7 Analytical Modeling of the Impact of Fiber Non-Linear Propagation on Coherent Systems and Networks 247 Pierluigi Poggiolini, Yanchao Jiang, Andrea Carena, and Fabrizio Forghieri 7.1 Why are Analytical Models Important?, 247 7.1.1 What Do Professionals Need?, 247 7.2 Background, 248 7.2.1 Modeling Approximations, 249 7.3 Introducing the GN–EGN Model Class, 260 7.3.1 Getting to the GN Model, 260 7.3.2 Towards the EGN Model, 265 7.4 Model Selection Guide, 269 7.4.1 From Model to System Performance, 269 7.4.2 Point-to-Point Links, 270 7.4.3 The Complete EGN Model, 272 7.4.4 Case Study: Determining the Optimum System Symbol Rate, 286 7.4.5 NLI Modeling for Dynamically Reconfigurable Networks, 289 7.5 Conclusion, 294 Acknowledgements, 295 Appendix, 295 A.1 The White-Noise Approximation, 295 A.1 BER Formulas for the Most Common QAM Systems, 295 A.2 The Link Function 𝜇, 296 A.3 The EGN Model Formulas for the X2-X4 and M1-M3 Islands, 297 A.4 Outline of GN–EGN Model Derivation, 299 A.5 List of Acronyms, 303 References, 305 8 Digital Equalization in Coherent Optical Transmission Systems 311 Seb Savory 8.1 Introduction, 311 8.2 Primer on the Mathematics of Least Squares FIR Filters, 312 8.2.1 Finite Impulse Response Filters, 313 8.2.2 Differentiation with Respect to a Complex Vector, 314 8.2.3 Least Squares Tap Weights, 314 8.2.4 Application to Stochastic Gradient Algorithms, 316 8.2.5 Application to Wiener Filter, 317 8.2.6 Other Filtering Techniques and Design Methodologies, 318 8.3 Equalization of Chromatic Dispersion, 318 8.3.1 Nature of Chromatic Dispersion, 318 8.3.2 Modeling of Chromatic Dispersion in an Optical Fiber, 318 8.3.3 Truncated Impulse Response, 319 8.3.4 Band-Limited Impulse Response, 320 8.3.5 Least Squares FIR Filter Design, 321 8.3.6 Example Performance of the Chromatic Dispersion Compensating Filter, 321 8.4 Equalization of Polarization-Mode Dispersion, 323 8.4.1 Modeling of PMD, 324 8.4.2 Obtaining the Inverse Jones Matrix of the Channel, 325 8.4.3 Constant Modulus Update Algorithm, 325 8.4.4 Decision-Directed Equalizer Update Algorithm, 326 8.4.5 Radially Directed Equalizer Update Algorithm, 327 8.4.6 Parallel Realization of the FIR Filter, 327 8.4.7 Generalized 4 × 4 Equalizer for Mitigation of Frequency or Polarization-Dependent Loss and Receiver Skew, 328 8.4.8 Example Application to Fast Blind Equalization of PMD, 328 8.5 Concluding Remarks and Future Research Directions, 329 Acknowledgments, 330 References, 330 9 Nonlinear Compensation for Digital Coherent Transmission 333 Guifang Li 9.1 Introduction, 333 9.2 Digital Backward Propagation (DBP), 334 9.2.1 How DBP Works, 334 9.2.2 Experimental Demonstration of DBP, 335 9.2.3 Computational Complexity of DBP, 336 9.3 Reducing DBP Complexity for Dispersion-Unmanaged WDM Transmission, 339 9.4 DBP for Dispersion-Managed WDM Transmission, 342 9.5 DBP for Polarization-Multiplexed Transmission, 349 9.6 Future Research, 350 References, 351 10 Timing Synchronization in Coherent Optical Transmission Systems 355 Han Sun and Kuang-Tsan Wu 10.1 Introduction, 355 10.2 Overall System Environment, 357 10.3 Jitter Penalty and Jitter Sources in a Coherent System, 359 10.3.1 VCO Jitter, 359 10.3.2 Detector Jitter Definitions and Method of Numerical Evaluation, 361 10.3.3 Laser FM Noise- and Dispersion-Induced Jitter, 363 10.3.4 Coherent System Tolerance to Untracked Jitter, 366 10.4 Digital Phase Detectors, 368 10.4.1 Frequency-Domain Phase Detector, 369 10.4.2 Equivalence to the Squaring Phase Detector, 371 10.4.3 Equivalence to Godard’s Maximum Sampled Power Criterion, 373 10.4.4 Equivalence to Gardner’s Phase Detector, 374 10.4.5 Second Class of Phase Detectors, 377 10.4.6 Jitter Performance of the Phase Detectors, 378 10.4.7 Phase Detectors for Nyquist Signals, 380 10.5 The Chromatic Dispersion Problem, 383 10.6 The Polarization-Mode Dispersion Problem, 386 10.7 Timing Synchronization for Coherent Optical OFDM, 390 10.8 Future Research, 391 References, 392 11 Carrier Recovery in Coherent Optical Communication Systems 395 Xiang Zhou 11.1 Introduction, 395 11.2 Optimal Carrier Recovery, 397 11.2.1 MAP-Based Frequency and Phase Estimator, 397 11.2.2 Cramér–Rao Lower Bound, 398 11.3 Hardware-Efficient Phase Recovery Algorithms, 399 11.3.1 Decision-Directed Phase-Locked Loop (PLL), 399 11.3.2 Mth-Power-Based Feedforward Algorithms, 401 11.3.3 Blind Phase Search (BPS) Feedforward Algorithms, 405 11.3.4 Multistage Carrier Phase Recovery Algorithms, 408 11.4 Hardware-Efficient Frequency Recovery Algorithms, 416 11.4.1 Coarse Auto-Frequency Control (ACF), 416 11.4.2 Mth-Power-Based Fine FO Estimation Algorithms, 418 11.4.3 Blind Frequency Search (BFS)-Based Fine FO Estimation Algorithm, 421 11.4.4 Training-Initiated Fine FO Estimation Algorithm, 423 11.5 Equalizer-Phase Noise Interaction and its Mitigation, 424 11.6 Carrier Recovery in Coherent OFDM Systems, 429 11.7 Conclusions and Future Research Directions, 430 References, 431 12 Real-Time Implementation of High-Speed Digital Coherent Transceivers 435 Timo Pfau 12.1 Algorithm Constraints, 435 12.1.1 Power Constraint and Hardware Optimization, 436 12.1.2 Parallel Processing Constraint, 438 12.1.3 Feedback Latency Constraint, 440 12.2 Hardware Implementation of Digital Coherent Receivers, 442 References, 446 13 Photonic Integration 447 Po Dong and Sethumadhavan Chandrasekhar 13.1 Introduction, 447 13.2 Overview of Photonic Integration Technologies, 449 13.3 Transmitters, 451 13.3.1 Dual-Polarization Transmitter Circuits, 451 13.3.2 High-Speed Modulators, 452 13.3.3 PLC Hybrid I/Q Modulator, 455 13.3.4 InP Monolithic I/Q Modulator, 455 13.3.5 Silicon Monolithic I/Q Modulator, 457 13.4 Receivers, 459 13.4.1 Polarization Diversity Receiver Circuits, 459 13.4.2 PLC Hybrid Receivers, 461 13.4.3 InP Monolithic Receivers, 462 13.4.4 Silicon Monolithic Receivers, 462 13.4.5 Coherent Receiver with 120∘ Optical Hybrids, 465 13.5 Conclusions, 467 Acknowledgments, 467 References, 467 14 Optical Performance Monitoring for Fiber-Optic Communication Networks 473 Faisal N. Khan, Zhenhua Dong, Chao Lu, and Alan Pak Tao Lau 14.1 Introduction, 473 14.1.1 OPM and Their Roles in Optical Networks, 474 14.1.2 Network Functionalities Enabled by OPM, 475 14.1.3 Network Parameters Requiring OPM, 477 14.1.4 Desirable Features of OPM Techniques, 480 14.2 OPM Techniques For Direct Detection Systems, 482 14.2.1 OPM Requirements for Direct Detection Optical Networks, 482 14.2.2 Overview of OPM Techniques for Existing Direct Detection Systems, 483 14.2.3 Electronic DSP-Based Multi-Impairment Monitoring Techniques for Direct Detection Systems, 485 14.2.4 Bit Rate and Modulation Format Identification Techniques for Direct Detection Systems, 488 14.2.5 Commercially Available OPM Devices for Direct Detection Systems, 489 14.2.6 Applications of OPM in Deployed Fiber-Optic Networks, 489 14.3 OPM For Coherent Detection Systems, 490 14.3.1 Non-Data-Aided OSNR Monitoring for Digital Coherent Receivers, 491 14.3.2 Data-Aided (Pilot Symbols Based) OSNR Monitoring for Digital Coherent Receivers, 494 14.3.3 OPM at the Intermediate Network Nodes Using Low-Cost Structures, 495 14.3.4 OSNR Monitoring in the Presence of Fiber Nonlinearity, 496 14.4 Integrating OPM Functionalities in Networking, 499 14.5 Conclusions and Outlook, 499 Acknowledgments, 500 References, 500 15 Rate-Adaptable Optical Transmission and Elastic Optical Networks 507 Patricia Layec, Annalisa Morea, Yvan Pointurier, and Jean-Christophe  Antona 15.1 Introduction, 507 15.1.1 History of Elastic Optical Networks, 509 15.2 Key Building Blocks, 511 15.2.1 Optical Cross-Connect, 512 15.2.2 Elastic Transponder, 513 15.2.3 Elastic Aggregation, 515 15.2.4 Performance Prediction, 516 15.2.5 Resource Allocation Tools, 520 15.2.6 Control Plane for Flexible Optical Networks, 524 15.3 Practical Considerations for Elastic WDM Transmission, 527 15.3.1 Flexible Transponder Architecture, 527 15.3.2 Example of a Real-Time Energy-Proportional Prototype, 529 15.4 Opportunities for Elastic Technologies in Core Networks, 530 15.4.1 More Cost-Efficient Networks, 531 15.4.2 More Energy Efficient Network, 532 15.4.3 Filtering Issues and Superchannel Solution, 532 15.5 Long Term Opportunities, 534 15.5.1 Burst Mode Elasticity, 534 15.5.2 Elastic Passive Optical Networks, 536 15.5.3 Metro and Datacenter Networks, 537 15.6 Conclusions, 539 Acknowledgments, 539 References, 539 16 Space-Division Multiplexing and MIMO Processing 547 Roland Ryf and Nicolas K. Fontaine 16.1 Space-Division Multiplexing in Optical Fibers, 547 16.2 Optical Fibers for SDM Transmission, 548 16.3 Optical Transmission in SDM Fibers with Low Crosstalk, 551 16.3.1 Digital Signal Processing Techniques for SDM Fibers with Low Crosstalk, 552 16.4 MIMO-Based Optical Transmission in SDM Fibers, 553 16.5 Impulse Response in SDM Fibers with Mode Coupling, 558 16.5.1 Multimode Fibers with no Mode Coupling, 561 16.5.2 Multimode Fibers with Weak Coupling, 561 16.5.3 Multimode Fibers with Strong Mode Coupling, 565 16.5.4 Multimode Fibers: Scaling to Large Number of Modes, 566 16.6 MIMO-Based SDM Transmission Results, 566 16.6.1 Digital Signal Processing for MIMO Transmission, 567 16.7 Optical Components for SDM Transmission, 568 16.7.1 Characterization of SDM Systems and Components, 570 16.7.2 Swept Wavelength Interferometry for Fibers with Multiple Spatial Paths, 571 16.7.3 Spatial Multiplexers, 576 16.7.4 Photonic Lanterns, 578 16.7.5 Spatial Diversity for SDM Components and Component sharing, 582 16.7.6 Wavelength-Selective Switches for SDM, 583 16.7.7 SDM Fiber Amplifiers, 590 16.8 Conclusion, 593 Acknowledgments, 593 References, 594 Index 609

About the Author :
Xiang Zhou is a Tech Lead within Google Platform Advanced Technology. Before joining Google, he was with AT&T Labs, conducting research on various aspects of optical transmission and photonics networking technologies. Dr. Zhou is an OSA fellow and an associate editor for Optics Express. He has extensive publications in the field of optical communications. Chongjin Xie is a Senior Director at Ali Infrastructure Service, Alibaba Group. Before joining Alibaba Group, he was a Distinguished Member of Technical Staff at Bell Labs, Alcatel-Lucent. Dr. Xie is a fellow of OSA and senior member of IEEE. He is an associate editor of the Journal of Lightwave Technology and has served in various conference committees.