Preface
Acknowledgements
Contents
1 Introduction: The Basics of Optical Communications
1.1 Introduction
1.2 Introduction to Optical Communications
1.2.1 The Basics of Optical Communications
1.2.2 A Remarkable Coincidence
1.2.3 Optical Amplifiers
1.2.4 A Complete Technology
1.3 A Picture of Semiconductor Lasers
1.4 Organization of the Book
1.5 Summary and Learning Points
1.6 Questions and Problems
2 The Basics of Lasers
2.1 Introduction
2.2 Introduction to Lasers
2.2.1 Black Body Radiation
2.2.2 Statistical Thermodynamics Viewpoint of Black Body Radiation
2.2.3 Some Probability Distribution Functions
2.2.4 Density of States
2.2.5 Spectrum of a Black Body
2.3 Black Body Radiation: Einsteinโs View
2.4 Implications for Lasing
2.5 Differences Between Spontaneous Emission, Stimulated Emission, and Lasing
2.6 Some Example of Laser Systems
2.6.1 Erbium-Doped Fiber Laser
2.6.2 HeNe Gas Laser
2.7 Summary and Learning Points
2.8 Questions
2.9 Problems
3 Semiconductors as Laser Materials 1: Fundamentals
3.1 Introduction
3.2 Energy Bands and Radiative Recombination
3.3 Semiconductor Laser Material System
3.4 Determining the Band Gap
3.4.1 Vegardโs Law: Ternary Compounds
3.4.2 Vegardโs Law: Quaternary Compounds
3.5 Lattice Constant, Strain, and Critical Thickness
3.5.1 Thin Film Epitaxial Growth
3.5.2 Strain and Critical Thickness
3.6 Direct and Indirect Bandgaps
3.6.1 Dispersion Diagrams
3.6.2 Features of Dispersion Diagrams
3.6.3 Direct and Indirect Band Gaps
3.6.4 Phonons
3.7 Summary and Learning Points
3.8 Questions
3.9 Problems
4 Semiconductors as Laser Materials 2: Density of States, Quantum Wells, and Gain
4.1 Introduction
4.2 Density of Electrons and Holes in a Semiconductor
4.2.1 Modifications to Eq.ย 4.9: Effective Mass
4.2.2 Modifications to Eq.ย 4.9: Including the Band Gap
4.3 Quantum Wells as Laser Materials
4.3.1 Energy Levels in an Ideal Quantum Well
4.3.2 Energy Levels in a Real Quantum Well
4.4 Density of States in a Quantum Well
4.5 Number of Carriers
4.5.1 Quasi-Fermi Levels
4.5.2 Number of Holes Versus Number of Electrons
4.6 Condition for Lasing
4.7 Optical Gain
4.8 Semiconductor Optical Gain
4.8.1 Joint Density of States
4.8.2 Occupancy Factor
4.8.3 Proportionality Constant
4.8.4 Linewidth Broadening
4.9 Summary and Learning Points
4.10 Learning Points
4.11 Questions
4.12 Problems
5 Semiconductor Laser Operation
5.1 Introduction
5.2 A Simple Semiconductor Laser
5.3 A Qualitative Laser Model
5.4 Absorption Loss
5.4.1 Band-to-Band and Free Carrier Absorption
5.4.2 Band-to-Impurity Absorption
5.5 Rate Equation Models
5.5.1 Carrier Lifetime
5.5.2 Consequences in Steady State
5.5.3 Units of Gain and Photon Lifetime
5.5.4 Slope Efficiency
5.6 Facet-Coated Devices
5.7 A Complete DC Analysis
5.8 Summary and Learning Points
5.9 Questions
5.10 Problems
6 Electrical Characteristics of Semiconductor Lasers
6.1 Introduction
6.2 Basics of pโn Junctions
6.2.1 Carrier Density as a Function of Fermi Level Position
6.2.2 Band Structure and Charges in pโn Junction
6.2.3 Currents in an Unbiased pโn Junction
6.2.3.1 Diffusion Current
6.2.3.2 Drift Current
6.2.4 Built-in Voltage
6.2.5 Width of Space Charge Region
6.3 Semiconductor pโn Junctions with Applied Bias
6.3.1 Applied Bias and Quasi-Fermi Levels
6.3.2 Recombination and Boundary Conditions
6.3.3 Minority Carrier Quasi-Neutral Region Diffusion Current
6.4 Semiconductor Laser pโn Junctions
6.4.1 Diode Ideality Factor
6.4.2 Clamping of Quasi-Fermi Levels at Threshold
6.5 Summary of Diode Characteristics
6.6 Metal Contact to Lasers
6.6.1 Definition of Energy Levels
6.6.2 Band Structures
6.7 Realization of Ohmic Contacts for Lasers
6.7.1 Current Conduction Through a MetalโSemiconductor Junction: Thermionic Emission
6.7.2 Current Conduction Through a MetalโSemiconductor Junction: Tunneling Current
6.7.3 Diode Resistance and Measurement of Contact Resistance
6.8 Summary and Learning Points
6.9 Questions
6.10 Problems
7 The Optical Cavity
7.1 Introduction
7.2 Chapter Outline
7.3 Overview of a Fabry-Perot Optical Cavity
7.4 Longitudinal Optical Modes Supported by a Laser Cavity
7.4.1 Optical Modes Supported by an Etalon: The Laser Cavity in 1D
7.4.2 Free Spectral Range in a Long Etalon
7.4.3 Free Spectral Range in a Fabry-Perot Laser Cavity
7.4.4 Optical Output of a Fabry-Perot Laser
7.4.5 Longitudinal Modes
7.5 Calculation of Gain from Optical Spectrum
7.6 Lateral Modes in an Optical Cavity
7.6.1 Importance of Lateral Modes in Real Lasers
7.6.2 Total Internal Reflection
7.6.3 Transverse Electric and Transverse Magnetic Modes
7.6.4 Quantitative Analysis of the Waveguide Modes
7.7 Two-Dimensional Waveguide Design
7.7.1 Confinement in Two Dimensions
7.7.2 Effective Index Method
7.7.3 Waveguide Design Targets for Lasers
7.8 Summary and Learning Points
7.9 Questions
7.10 Problems
8 Laser Modulation
8.1 Introduction: Digital and Analog Optical Transmission
8.2 Specifications for Digital Transmission
8.3 Small Signal Laser Modulation
8.3.1 Measurement of Small Signal Modulation
8.3.2 Small Signal Modulation of LEDs
8.3.3 Rate Equations for Lasers, Revisited
8.3.4 Derivation of Small Signal Homogenous Laser Response
8.3.5 Small Signal Laser Homogenous Response
8.4 Laser AC Current Modulation
8.4.1 Outline of the Derivation
8.4.2 Laser Modulation Measurement and Equation
8.4.3 Analysis of Laser Modulation Response
8.4.4 Demonstration of the Effects of ฯc
8.5 Limits to Laser Bandwidth
8.6 Relative Intensity Noise Measurements
8.7 Large Signal Modulation
8.7.1 Modeling the Eye Pattern
8.7.2 Considerations for Laser Systems
8.8 Summary and Conclusions
8.9 Learning Points
8.10 Questions
8.11 Problems
9 Distributed Feedback Lasers
9.1 A Single-Wavelength Laser
9.2 Need for Single-Wavelength Lasers
9.2.1 Realization of Single-Wavelength Devices
9.2.2 Narrow Gain Medium
9.2.3 High Free Spectral Range and Moderate Gain Bandwidth
9.2.4 External Bragg Reflectors
9.3 Distributed Feedback Lasers: Overview
9.3.1 Distributed Feedback Lasers: Physical Structure
9.3.2 Bragg Wavelength and Coupling
9.3.3 Unity Round Trip Gain
9.3.4 Gain Envelope
9.3.5 Distributed Feedback Lasers: Design and Fabrication
9.3.6 Distributed Feedback Lasers: Zero Net Phase
9.4 Experimental Data from Distributed Feedback Lasers
9.4.1 Influence of ฮบ on Threshold Current and Slope Efficiency
9.4.2 Influence of Phase on Threshold Current
9.4.3 Influence of Phase on Cavity Power Distribution and Slope
9.4.4 Influence of Phase on Single-Mode Yield
9.5 Modeling of Distributed Feedback Lasers
9.6 Coupled Mode Theory
9.6.1 A Graphical Picture of Diffraction
9.6.2 Coupled Mode Theory in Distributed Feedback Laser
9.6.3 Measurement of ฮบ
9.7 Inherently Single-Mode Lasers
9.8 Other Types of Gratings
9.9 Learning Points
9.10 Questions
9.11 Problems
10 Assorted Miscellany: Dispersion, Fabrication, and Reliability
10.1 Introduction
10.2 Dispersion and Single Mode Devices
10.3 Temperature Effects on Lasers
10.3.1 Temperature Effects on Wavelength
10.3.2 Temperature Effects on DC Properties
10.4 Laser Fabrication: Wafer Growth, Wafer Fabrication, Chip Fabrication, and Testing
10.4.1 Substrate Wafer Fabrication
10.4.2 Laser Design
10.4.3 Heterostructure Growth
10.4.3.1 Heterostructure Growth: Molecular Beam Epitaxy (MBE)
10.4.3.2 Heterostructure Growth: Metallorganic Chemical Vapor Deposition (MOCVD)
10.5 Grating Fabrication
10.5.1 Grating Fabrication
10.5.2 Grating Overgrowth
10.6 Wafer Fabrication
10.6.1 Wafer Fabrication: Ridge Waveguide
10.6.2 Wafer Fabrication: Buried Heterostructure Versus Ridge Waveguide
10.6.3 Wafer Fabrication: Vertical Cavity Surface-Emitting Lasers (VCSELS)
10.7 Chip Fabrication
10.8 Wafer Testing and Yield
10.9 Reliability
10.9.1 Individual Device Testing and Failure Modes
10.9.2 Definition of Failure
10.9.3 Arrhenius Dependence of Aging Rates
10.9.4 Analysis of Aging Rates, FITS, and MTBF
10.9.5 Electrostatic Discharge and Electrical Overstresses
10.9.6 Optical Overstress and Snap Test
10.10 Design for โฆ
10.10.1 Design Tools
10.10.2 Design for High Speed Directly Modulated Lasers
10.10.3 Design for High Power
10.10.4 Design for Low Linewidth
10.10.5 Design Over Temperature
10.11 Summary and Learning Points
10.12 Questions
10.13 Problems
11 Laser Communication Systems I: Amplitude Modulated Systems
11.1 Introduction
11.2 Evolution of Optical Speed
11.3 Evolutionary Changes
11.4 Multiplexing
11.4.1 Wavelength Division Multiplexing
11.4.2 Wavelength Division Multiplexing and Demultiplexing
11.4.3 Optical Add Drop Multiplexors
11.5 Overview of Amplitude-Modulated Communication
11.5.1 Definitions for Amplitude Modulation Formats
11.5.2 Bits Versus Symbols
11.5.3 Pulse Amplitude Modulation
11.6 External Modulation
11.6.1 Quantum-Confined Stark Effect
11.6.2 Absorption Modulation Through the Quantum-Confined Stark Effect
11.6.3 MachโZehnder Modulator from Electooptic Materials
11.6.4 Phase Shifting with Plasma Effect
11.7 Laser Linewidth
11.7.1 Inherent Laser Linewidth
11.7.2 Linewidth Enhancement Factor
11.8 Direct Detection Receivers
11.9 Summary and Learning Points
11.10 Questions
11.11 Problems
12 Coherent Communication Systems
12.1 Introduction
12.2 Phasor Representation of Light
12.2.1 Reminder: Phasor Representation of Electrical Signals
12.2.2 Phasor Representation of Optical Signals
12.3 Phasor Descriptions of Coherent Optical Transmission
12.3.1 Binary (and More) Phase Shift Keying
12.3.2 Differential Phase Shift Keying
12.3.3 Quadrature Amplitude Modulation
12.3.4 Polarization Division Multiplexing
12.3.5 Polarization-Maintaining Fiber
12.4 Coherent Optical Transmitters
12.4.1 Binary (or More) Phase Shift Keying Transmitter
12.4.2 Quadrature Amplitude Modulation
12.5 Receivers
12.5.1 Reference Signal
12.5.2 Balanced Photodiode
12.5.3 A Full Coherent System
12.6 Coherent Transmission in Context
12.6.1 Comparison of Coherent and Incoherent (Amplitude Shift Keying) Systems
12.6.2 Communication Formats
12.7 Limits to Transmission Distance in Optical Systems
12.7.1 Optical Signal-to-Noise Ratio
12.7.2 Eye Diagram-Based Signal-to-Noise Ratio
12.7.3 Bit Error Rate Versus Transmission Format and Signal-to-Noise Ratio
12.8 Noise Sources
12.8.1 Relative Intensity Noise
12.8.2 Shot Noise
12.8.3 Erbium-Doped Fiber Amplifier Noise
12.8.4 Thermal Johnson Noise
12.8.5 Combination of Noise Sources
12.8.6 Other Noise Sources
12.9 Final Words
12.10 Summary and Learning Points
12.11 Questions
12.12 Problems
Index