Ultrafast Lasers Based on Quantum Dot Structures: Physics and Devices

In this monograph, the authors address the physics and engineering together with the latest achievements of efficient and compact ultrafast lasers based on novel quantum-dot structures and devices. Their approach encompasses a broad range of laser systems, while taking into consideration not only the physical and experimental aspects but also the much needed modeling tools, thus providing a holistic understanding of this hot topic.

Table of Contents:
Introduction IX Acknowledgments XI 1 Semiconductor Quantum Dots for Ultrafast Optoelectronics 1 1.1 The Role of Dimensionality in Semiconductor Materials 1 1.2 Material Systems Used 4 1.2.1 III–V Epitaxially Grown Quantum Dots 4 1.2.2 QD-Doped Glasses 6 1.2.3 Quantum Dashes 6 1.3 Quantum Dots: Distinctive Properties for Ultrafast Devices 7 1.3.1 Inhomogeneous Broadening 7 1.3.2 Ultrafast Carrier Dynamics 9 2 Foundations of Quantum Dot Theory 11 2.1 Energy Structure and Matrix Elements 11 2.2 Theoretical Approaches to Calculating Absorption and Gain in Quantum Dots 14 2.3 Kinetic Theory of Quantum Dots 22 2.4 Light–Matter Interactions in Quantum Dots 37 2.5 The Nonlinearity Coefficient 51 3 Quantum Dots in Amplifiers of Ultrashort Pulses 55 3.1 Optical Amplifiers for High-Speed Applications: Requirements and Problems 55 3.2 Quantum Dot Optical Amplifiers: Short-Pulse Operating Regime 62 3.3 Quantum Dot Optical Amplifiers at High Bit Rates: Low Distortions and Patterning-Free Operation 63 3.4 Nonlinear Operation and Limiting Function Using QD Optical Amplifiers 76 4 Quantum Dot Saturable Absorbers 77 4.1 Foundations of Saturable Absorber Operation 77 4.2 The General Physical Principles of Saturable Absorption in Semiconductors 80 4.2.1 Physical Processes in a Saturable Absorber 80 4.2.2 Geometry of Saturable Absorber: SESAM versus Waveguide Absorber – The Cavity Enhancement of Saturable Absorption and the Standing Wave Factor in SESAMs 84 4.3 The Main Special Features of a Quantum Dot Saturable Absorber Operation 87 4.3.1 Bandwidth of QD SAs 88 4.3.2 Dynamics of Carrier Relaxation: Ultrafast Recovery of Absorption 88 4.3.3 Saturation Fluence 94 5 Monolithic Quantum Dot Mode-Locked Lasers 99 5.1 Introduction to Semiconductor Mode-Locked Lasers 99 5.1.1 Place of Semiconductor Mode-Locked Lasers Among Other Ultrashort Pulse Sources 99 5.1.2 Mode-Locking Techniques in Laser Diodes: The Main Principles 100 5.1.3 Passive Mode Locking: The Qualitative Picture, Physics, and Devices 101 5.2 Theoretical Models of Mode Locking in Semiconductor Lasers 103 5.2.1 Small-Signal Time Domain Models: Self-Consistent Pulse Profile 103 5.2.2 Large-Signal Time Domain Approach: Delay Differential Equations Model 109 5.2.3 Traveling Wave Models 120 5.2.4 Frequency and Time–Frequency Treatment of Mode Locking: Dynamic Modal Analysis 125 5.3 Main Predictions of Generic Mode-Locked Laser Models and their Implication for Quantum Dot Lasers 126 5.3.1 Laser Performance Depending on the Operating Point 126 5.3.2 Main Parameters that Affect Mode-Locked Laser Behavior 129 5.4 Specific Features of Quantum Dot Mode-Locked Lasers in Theory and Modeling 131 5.4.1 Delay Differential Equation Model for Quantum Dot Mode-Locked Lasers 132 5.4.2 Traveling Wave Modeling of Quantum Dot Mode-Locked Lasers: Effects of Multiple Levels and Inhomogeneous Broadening 141 5.4.3 Modal Analysis for QD Mode-Locked Lasers 153 5.5 Advantages of Quantum Dot Materials in Mode-Locked Laser Diodes 154 5.5.1 Advantages of QD Saturable Absorbers 154 5.5.2 Broad Gain Bandwidth 154 5.5.3 Low Threshold Current 155 5.5.4 Low Temperature Sensitivity 155 5.5.5 Suppressed Carrier Diffusion 156 5.5.6 Lower Level of Amplified Spontaneous Emission 157 5.5.7 Linewidth Enhancement Factor 157 5.6 Ultrashort Pulse Generation: Achievements and Strategies 158 5.6.1 Monolithic Mode-Locked Quantum Dot Lasers 158 5.6.2 Chirp Measurement and Pulse Compression 161 5.6.3 Toward Higher Power: Tapered Lasers 164 5.6.4 Toward Higher Repetition Rates 165 5.6.5 External Cavity QD Mode-Locked Lasers 166 5.7 Noise Characteristics of QD Mode-Locked Lasers 167 5.7.1 Timing Jitter 167 5.7.2 Pulse Repetition Rate Stability and Resilience to Optical Feedback 170 5.7.3 Performance Under Optical Injection 172 5.8 Performance of QD Mode-Locked Lasers at Elevated Temperature 174 5.8.1 Stable Mode Locking at Elevated Temperature 174 5.8.2 Pulse Duration Trends at Higher Temperatures 175 5.8.3 The Use of p-Doping in QD Mode-Locked Lasers 176 5.9 Exploiting Different Transitions for Pulse Generation 176 5.9.1 Mode Locking via Ground and Excited States 176 5.9.2 The Excited-State Transition as Tool for Novel Mode-Locking Regimes 179 5.10 Summary and Outlook 180 5.10.1 QD Mode-Locked Laser Diodes: New Functionalities 180 5.10.2 Future Directions 181 6 Ultrashort Pulse Solid State Lasers Based on Quantum Dot Saturable Absorbers 183 6.1 A Brief Historical Overview of Ultrashort-Pulse Generation 183 6.2 Macroscopic Parameters of Saturable Absorbers 184 6.3 QD SESAMs for Efficient Passive Mode Locking of Solid-State Lasers Emitted around 1 mm 187 6.4 QD SESAMs for Efficient Passive Mode Locking of Solid-State Lasers Emitted around 1.3 mm 193 6.5 QD SESAMs for the Passive Mode Locking of Fiber Lasers 199 6.6 Mode-Locked Semiconductor Disk Lasers Incorporating QD SESAMs 201 6.7 Optically Pumped Quantum Dot VECSELs 204 7 Saturable Absorbers Based on QD-Doped Glasses 207 7.1 II–VI Semiconductor Nanocrystals in Glass 207 7.2 IV–VI Semiconductor QD-Doped Glasses for Ultrashort-Pulse Generation from Solid-State Lasers 209 7.3 QD-Doped Glass Saturable Absorbers for Passive Mode Locking around 1.3 mm 210 7.4 Cr:YAG Laser Passively Mode Locked with a QD-Doped Glass Saturable Absorber 212 7.5 PbS QD-Doped Glass Saturable Absorbers for Passive Mode Locking around 1 mm and Their Nonlinear Characteristics 214 8 Emerging Applications of Ultrafast Quantum Dot Lasers 217 8.1 Optical Communications 217 8.2 Datacoms 219 8.3 Biophotonics and Medical Applications 220 8.4 Outlook 220 References 223 Index 241

About the Author :
Eugene Avrutin has been working in the field of theory, numerical modelling, and computer-added design of semiconductor optoelectronic devices since 1986. Having previously been a researcher at the A.F. Ioffe Institute, St Petersburg (till 1993), and a research assistant in the University of Glasgow (1994-1999), he has held an academic position at the University of York since 2000. He has published two book chapters, more than 70 peer-reviewed journal papers and over a hundred conference papers, many of them in the field of fast and ultrafast laser sources and/or reduced dimensionality semiconductors. Maria Ana Cataluna is a lecturer and a Royal Academy of Engineering/EPSRC Research Fellow at the University of Dundee (UK). She has been committed to research in ultrafast laser physics and technology development since 2000, having previously worked at the Instituto Superior Técnico, Portugal (2000-2002), at the University of St. Andrews, UK (2003-2007), subsequently joining the University of Dundee in 2007. She was awarded the IEEE Photonics Society Graduate Student Fellowship (2007), for her work on innovative mode-locking regimes in ultrafast quantum-dot based lasers. She has published more than 50 papers in peer-reviewed journals and conference proceedings and three invited book chapters. Edik Rafailov has been engaged in the research and development of high-power cw and ultrashort pulse lasers, nonlinear and integrated optics since 1987. In 2005 he moved to Dundee University as a lecturer and established a new Photonics and Nanoscience group. In 2008 he became a reader and two years later a professor. He was previously a senior researcher at Ioffe Institute, St Petersburg (1987-1997) and a research fellow at the University of St. Andrews (1997-2005). He has authored and co-authored over 220 articles in refereed journals and conference proceedings, three invited chapters and numerous invited talks to CLEO, SPIE and LEOS. He also holds 8 UK and two US patents. Professor Rafailov is the coordinator of projects funded by EU FP7 program and EPSRC. His current research interests include novel high-power CW, short, ultrashort-pulse and high-repetition rate lasers; generation of UV/visible/IR and THz radiation, nano-structures; nonlinear optics and Biophotonics.