Fiber Optic Communications

Preface
	Use of This Book
Acknowledgements
Contents
About the Author
1 Perspectives on Lightwave Communications
	1.1 Reasons for Fiber Optic Communications
		1.1.1 The Road to Optical Networks
		1.1.2 Benefits of Using Optical Fibers
	1.2 Optical Wavelength Bands
		1.2.1 Electromagnetic Energy Spectrum
		1.2.2 Optical Windows and Spectral Bands
	1.3 Decibel Notation
	1.4 Digital Multiplexing Techniques
		1.4.1 Basic Telecom Signal Multiplexing
		1.4.2 Multiplexing Hierarchy in SONET/SDH
		1.4.3 Optical Transport Network (OTN)
	1.5 Multiplexing of Wavelength Channels
		1.5.1 Basis of WDM
		1.5.2 Polarization Division Multiplexing
		1.5.3 Optical Fibers with Multiple Cores
	1.6 Basic Elements of Optical Fiber Systems
	1.7 Evolution of Fiber Optic Networks
	1.8 Standards for Fiber Optic Communications
	1.9 Summary
	References
2 Optical Fiber Structures and Light Guiding Principles
	2.1 The Nature of Light
		2.1.1 Polarization
		2.1.2 Linear Polarization
		2.1.3 Elliptical Polarization and Circular Polarization
		2.1.4 Quantum Aspects of Light
	2.2 Basic Laws and Definitions of Optics
		2.2.1 Concept of Refractive Index
		2.2.2 Basis of Reflection and Refraction
		2.2.3 Polarization Characteristics of Light
		2.2.4 Polarization-Sensitive Devices
	2.3 Optical Fiber Configurations and Modes
		2.3.1 Conventional Fiber Types
		2.3.2 Concepts of Rays and Modes
		2.3.3 Structure of Step-Index Fibers
		2.3.4 Ray Optics Representation
		2.3.5 Lightwaves in a Dielectric Slab Waveguide
	2.4 Modes in Circular Waveguides
		2.4.1 Basic Modal Concepts
		2.4.2 Cutoff Wavelength and V Number
		2.4.3 Optical Power in Step-Index Fibers
		2.4.4 Linearly Polarized Modes
	2.5 Single-Mode Fibers
		2.5.1 SMF Construction
		2.5.2 Definition of Mode–Field Diameter
		2.5.3 Origin of Birefringence
		2.5.4 Effective Refractive Index
	2.6 Graded-Index (GI) Fibers
		2.6.1 Core Structure of GI Fibers
		2.6.2 GI Fiber Numerical Aperture
		2.6.3 Cutoff Condition in GI Fibers
	2.7 Optical Fiber Materials
		2.7.1 Glass Optical Fibers
		2.7.2 Standard Fiber Fabrication
		2.7.3 Active Glass Optical Fibers
		2.7.4 Plastic Optical Fibers
	2.8 Photonic Crystal Fiber Concepts
		2.8.1 Index-Guiding PCF
		2.8.2 Photonic Bandgap Fiber
	2.9 Optical Fiber Cables
		2.9.1 Fiber Optic Cable Structures
		2.9.2 Designs of Indoor Optical Cables
		2.9.3 Designs of Outdoor Optical Cables
	2.10 Summary
	Appendix: The Fresnel Equations
	References
3 Optical Signal Attenuation and Dispersion
	3.1 Fiber Attenuation
		3.1.1 Units for Fiber Attenuation
		3.1.2 Absorption of Optical Power
		3.1.3 Scattering Losses in Optical Fibers
		3.1.4 Fiber Bending Losses
		3.1.5 Core and Cladding Propagation Losses
	3.2 Optical Signal Dispersion Effects
		3.2.1 Origins of Signal Dispersion
		3.2.2 Modal Delay Effects
		3.2.3 Factors Contributing to Dispersion
		3.2.4 Group Delay Results
		3.2.5 Material-Induced Dispersion
		3.2.6 Effects of Waveguide Dispersion
		3.2.7 Dispersion Behavior in Single-Mode Fibers
		3.2.8 Origin of Polarization-Mode Dispersion
	3.3 Design and Characteristics of SMFs
		3.3.1 Tailoring of Refractive Index Profiles
		3.3.2 Concept of Cutoff Wavelength
		3.3.3 Standards for Dispersion Calculations
		3.3.4 Definition of Mode-Field Diameter
		3.3.5 Bending Loss in Single-Mode Fibers
	3.4 ITU-T Standards for Fibers
		3.4.1 Recommendation G.651.1
		3.4.2 Recommendation G.652
		3.4.3 Recommendation G.653
		3.4.4 Recommendation G.654
		3.4.5 Recommendation G.655
		3.4.6 Recommendation G.656
		3.4.7 Recommendation G.657
	3.5 Designs and Use of Specialty Fibers
	3.6 Character of Multicore Optical Fibers
	3.7 Summary
	References
4 Light Sources for Fiber Links
	4.1 Basic Concepts of Semiconductor Physics
		4.1.1 Semiconductor Energy Bands
		4.1.2 Intrinsic and Extrinsic Materials
		4.1.3 Concept of a pn Junction
		4.1.4 Direct Bandgap and Indirect Bandgap
		4.1.5 Fabrication of Semiconductor Devices
	4.2 Principles of Light-Emitting Diodes (LEDs)
		4.2.1 LED Structures
		4.2.2 Semiconductor Materials for Light Sources
		4.2.3 LED Quantum Efficiency and Output Power
		4.2.4 Response Time of an LED
	4.3 Principles of Laser Diodes
		4.3.1 Modes and Threshold Conditions in Laser Diodes
		4.3.2 Laser Diode Rate Equations
		4.3.3 External Differential Quantum Efficiency
		4.3.4 Laser Resonant Frequencies
		4.3.5 Structures and Radiation Patterns of Laser Diodes
		4.3.6 Lasers Operating in a Single Mode
		4.3.7 Modulation of Laser Diodes
		4.3.8 Laser Output Spectral Width
		4.3.9 External Laser Light Modulation
		4.3.10 Lasing Threshold Temperature Effects
	4.4 Output Linearity of Light Sources
	4.5 Summary
	References
5 Optical Power Coupling
	5.1 Source-to-Fiber Power Coupling
		5.1.1 Light Source Emission Patterns
		5.1.2 Calculation of Power Coupling
		5.1.3 Optical Coupling Versus Wavelength
		5.1.4 Equilibrium Numerical Aperture
	5.2 Coupling Improvement with Lensing Schemes
	5.3 Losses Between Fiber Joints
		5.3.1 Mechanical Misalignment Effects
		5.3.2 Fiber Variation Losses
		5.3.3 Single-Mode Fiber Losses
		5.3.4 Preparation of Fiber End Faces
	5.4 Summary
	References
6 Photodetection Devices
	6.1 Operation of Photodiodes
		6.1.1 The pin Photodetector
		6.1.2 Basics of Avalanche Photodiodes
	6.2 Noise Effects in Photodetectors
		6.2.1 Signal-to-Noise Ratio
		6.2.2 Sources of Photodetector Noise
		6.2.3 Signal-to-Noise Ratio Limits
		6.2.4 Noise-Equivalent Power and Detectivity
	6.3 Response Times of Photodiodes
		6.3.1 Photocurrent in the Depletion Layer
		6.3.2 Response Time Characteristics
	6.4 Comparisons of Photodetectors
	6.5 Summary
	References
7 Optical Receiver Operation
	7.1 Basic Receiver Operation
		7.1.1 Transmitting Digital Signals
		7.1.2 Sources of Detection Errors
		7.1.3 Receiver Front-End Amplifiers
	7.2 Performance Characteristics of Digital Receivers
		7.2.1 Determining Probability of Error
		7.2.2 Specifying Receiver Sensitivity
		7.2.3 The Basic Quantum Limit
	7.3 Principles of Eye Diagrams
		7.3.1 Features of Eye Patterns
		7.3.2 BER and Q-Factor Measurements
	7.4 Burst-Mode Receivers
	7.5 Characteristics of Analog Receivers
	7.6 Summary
	References
8 Digital Optical Fiber Links
	8.1 Basic Optical Fiber Links
		8.1.1 Signal Formats for Transporting Information
		8.1.2 Considerations for Designing Links
		8.1.3 Creating a Link Power Budget
		8.1.4 Formulating a Rise-Time Budget
		8.1.5 Transmission at Short Wavelengths
		8.1.6 Attenuation Limits for SMF Links
	8.2 Concepts of Link Power Penalties
		8.2.1 Power Penalties from Chromatic Dispersion
		8.2.2 Power Penalties Arising from PMD
		8.2.3 Extinction Ratio Power Penalties
		8.2.4 Modal Noise Power Penalties
		8.2.5 Power Penalties Due to Mode-Partition Noise
		8.2.6 Chirping-Induced Power Penalties
		8.2.7 Link Instabilities from Reflection Noise
	8.3 Detection and Control of Errors
		8.3.1 Concept of Error Detection
		8.3.2 Codes Used for Linear Error Detection
		8.3.3 Error Detection with Polynomial Codes
		8.3.4 Using Redundant Bits for Error Correction
	8.4 Coherent Detection Schemes
		8.4.1 Fundamental Concepts
		8.4.2 Homodyne Detection
		8.4.3 Heterodyne Detection
		8.4.4 SNR in Coherent Detection
		8.4.5 BER Comparisons in Coherent Detection
	8.5 Higher-Order Signal Modulation Formats
		8.5.1 Concept of Spectral Efficiency
		8.5.2 Phase Shift Keying or IQ Modulation
		8.5.3 Differential Quadrature Phase-Shift Keying
		8.5.4 Quadrature Amplitude Modulation (QAM)
	8.6 Summary
	References
9 Analog Optical Fiber Channels
	9.1 Basic Elements of Analog Links
	9.2 Concept of Carrier-to-Noise Ratio
		9.2.1 Carrier Power
		9.2.2 Photodetector and Preamplifier Noises
		9.2.3 Effects of Relative Intensity Noise (RIN)
		9.2.4 Limiting C/N Conditions
	9.3 Multichannel Amplitude Modulation
	9.4 Spurious-Free Dynamic Range
	9.5 Radio-Over-Fiber Links
	9.6 Microwave Photonics
	9.7 Summary
	References
10 Wavelength Division Multiplexing (WDM)
	10.1 Concepts of WDM
		10.1.1 WDM Operational Principles
		10.1.2 Standards for WDM
	10.2 Passive Optical Couplers
		10.2.1 The 2 × 2 Fiber Coupler
		10.2.2 Scattering Matrix Analyses of Couplers
		10.2.3 Basis of the 2 × 2 Waveguide Coupler
		10.2.4 Principal Role of Star Couplers
		10.2.5 Mach–Zehnder Interferometry Techniques
	10.3 Nonreciprocal Isolators and Circulators
		10.3.1 Functions of Optical Isolators
		10.3.2 Characteristics of Optical Circulators
	10.4 WDM Devices Based on Grating Principles
		10.4.1 Grating Basics
		10.4.2 Optical Fiber Bragg Grating (FBG)
		10.4.3 WDM FBG Applications
	10.5 Dielectric Thin-Film Filter (TFF)
		10.5.1 Applications of Etalon Theory
		10.5.2 TFF Applications to WDM Links
	10.6 Arrayed Waveguide Devices
	10.7 WDM Applications of Diffraction Gratings
	10.8 Summary
	References
11 Basics of Optical Amplifiers
	11.1 Fundamental Optical Amplifier Types
		11.1.1 General Applications of Optical Amplifiers
		11.1.2 Amplifier Classifications
	11.2 Semiconductor Optical Amplifiers
		11.2.1 External Pumping of Active Medium
		11.2.2 Amplifier Signal Gain
		11.2.3 SOA Bandwidth
	11.3 Erbium-Doped Fiber Amplifiers
		11.3.1 Basics of Fiber Amplifier Pumping
		11.3.2 Construction of an EDFA
		11.3.3 EDFA Power-Conversion Efficiency and Gain
	11.4 Noises Generated in Optical Amplifiers
	11.5 Optical Signal-To-Noise Ratio (OSNR)
	11.6 Fiber Link Applications
		11.6.1 Power Amplifier Functions
		11.6.2 Use of In-Line Amplifiers
		11.6.3 Optical Amplifier as a Preamplifier
	11.7 Raman Optical Amplifiers
		11.7.1 Principle of Raman Gain
		11.7.2 Pump Lasers for Raman Amplifiers
	11.8 Multiband Optical Amplifiers
	11.9 Overview of Optical Fiber Lasers
	11.10 Summary
	References
12 Nonlinear Processes in Optical Fibers
	12.1 Classifications of Nonlinearities
	12.2 Effective Length and Effective Area
	12.3 Stimulated Raman Scattering
	12.4 Stimulated Brillouin Scattering
	12.5 Self-Phase Modulation
	12.6 Cross-Phase Modulation in WDM Systems
	12.7 Four-Wave Mixing in WDM Channels
	12.8 Mitigation Schemes for FWM
	12.9 Basic Optical Wavelength Converters
		12.9.1 Wavelength Converters Using Optical Gatings
		12.9.2 Wavelength Converters Based on Wave-Mixing
	12.10 Principles of Solitons
		12.10.1 Structures of Soliton Pulses
		12.10.2 Fundamental Parameters for Solitons
		12.10.3 Width and Spacing of Soliton Pulses
	12.11 Summary
	References
13 Fiber Optic Communication Networks
	13.1 Concepts of Optical Networks
		13.1.1 Terminology Used for Networks
		13.1.2 Generic Network Categories
		13.1.3 Layered Structure Approach to Network Architectures
		13.1.4 Optical Layer Functions
	13.2 Common Network Topologies
		13.2.1 Performance of Passive Linear Buses
		13.2.2 Performance of Star Networks
	13.3 Basic SONET/SDH Concepts
		13.3.1 SONET/SDH Frame Formats and Speeds
		13.3.2 Optical Interfaces in SONET/SDH
		13.3.3 SONET/SDH Rings
		13.3.4 SONET/SDH Network Architectures
	13.4 High-Speed Lightwave Transceivers
		13.4.1 Links Operating at 10 Gb/s
		13.4.2 Transceivers for 40 Gb/s Links
		13.4.3 Transceivers for 100 Gb/s Links
		13.4.4 Links Operating at 400 Gb/s and Higher
	13.5 Schemes for Optical Add/Drop Multiplexing
		13.5.1 Configurations of OADM Equipment
		13.5.2 Reconfiguring OADM Equipment
	13.6 Optical Switching Architectures
		13.6.1 Concept of an Optical Crossconnect
		13.6.2 Considerations for Wavelength Conversion
		13.6.3 Methodologies for Wavelength Routing
		13.6.4 Optical Packet Switching
		13.6.5 Optical Burst Switching
		13.6.6 Elastic Optical Networks
	13.7 WDM Network Implementations
		13.7.1 Long-Distance WDM Networks
		13.7.2 Metro WDM Networks
		13.7.3 Data Center Networks
	13.8 Passive Optical Networks
		13.8.1 Basic Architectures for PONs
		13.8.2 Active PON Modules
		13.8.3 Controlling PON Traffic Flows
		13.8.4 Protection Switching for PON Configurations
		13.8.5 WDM PON Architectures
	13.9 Summary
	References
14 Basic Measurement and Monitoring Techniques
	14.1 Overview of Measurement Standards
	14.2 Survey of Test Equipment
		14.2.1 Lasers Used for Test Support
		14.2.2 Optical Spectrum Analyzer
		14.2.3 Multipurpose Test Equipment
		14.2.4 Optical Attenuators
		14.2.5 OTN Tester for Performance Verification
		14.2.6 Visual Fault Indicator
	14.3 Optical Power Measurement Methods
		14.3.1 Physical Basis of Optical Power
		14.3.2 Optical Power Meters
	14.4 Characterization of Optical Fibers
		14.4.1 Refracted Near-Field Method
		14.4.2 Transmitted Near-Field Technique
		14.4.3 Optical Fiber Attenuation Measurements
	14.5 Concept of Eye Diagram Tests
		14.5.1 Standard Mask Testing
		14.5.2 Stressed Eye Opening
		14.5.3 BER Contours
	14.6 Optical Time-Domain Reflectometer
		14.6.1 OTDR Trace Characterization
		14.6.2 Attenuation Measurements with an OTDR
		14.6.3 OTDR Dead Zone
		14.6.4 Locating Fiber Faults
		14.6.5 Measuring Optical Return Loss
	14.7 Optical Performance Monitoring
		14.7.1 Network Management Systems and Functions
		14.7.2 Optical Layer Management
		14.7.3 Fundamental OPM Function
		14.7.4 OPM Architecture for Network Maintenance
		14.7.5 Detecting Network Faults
	14.8 Optical Fiber Network Performance Testing
		14.8.1 BER Measurements
		14.8.2 OSNR Measurements
		14.8.3 Q Factor Estimation
		14.8.4 OMA Measurement Method
		14.8.5 Measurement of Timing Jitter
	14.9 Summary
	References
Appendix A International Units and Physical Constants
Appendix B Decibels
B.1 Definition
B.2 The dBm
B.3 The Neper
Appendix C Acronyms
Appendix D List of Important Roman Symbols
Appendix E List of Important Greek Symbols