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

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.

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

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.