Nonlinear photonics in mid-infrared quantum cascade lasers : doctoral thesis accepted by Télécom ParisTech and mirSense, Paris, France

This thesis presents the first comprehensive analysis of quantum cascade laser nonlinear dynamics and includes the first observation of a temporal chaotic behavior in quantum cascade lasers. It also provides the first analysis of optical instabilities in the mid-infrared range. Mid-infrared quantum cascade lasers are unipolar semiconductor lasers, which have become widely used in applications such as gas spectroscopy, free-space communications or optical countermeasures. Applying external perturbations such as optical feedback or optical injection leads to a strong modification of the quantum cascade laser properties. Optical feedback impacts the static properties of mid-infrared Fabry–Perot and distributed feedback quantum cascade lasers, inducing power increase; threshold reduction; modification of the optical spectrum, which can become either single- or multimode; and enhanced beam quality in broad-area transverse multimode lasers. It also leads to a different dynamical behavior, and a quantum cascade laser subject to optical feedback can oscillate periodically or even become chaotic. A quantum cascade laser under external control could therefore be a source with enhanced properties for the usual mid-infrared applications, but could also address new applications such as tunable photonic oscillators, extreme events generators, chaotic Light Detection and Ranging (LIDAR), chaos-based secured communications or unpredictable countermeasures. Supervisor’s Foreword 6 Abstract 9 Preface 10 Preface 12 Journal Publications 12 Invited Conference Presentations 12 Conference Presentations 12 Acknowledgements 15 Contents 17 Acronyms 21 1 Introduction 22 1.1 The Need for Mid-infrared Sources 22 1.1.1 Applications at Mid-infrared Wavelengths 22 1.1.2 Available Mid-infrared Sources 24 1.2 Organization of the Dissertation 27 References 28 2 Quantum Cascade Lasers: High Performance Mid-infrared Sources 30 2.1 Principle of Operation 31 2.2 Theory 33 2.2.1 Heterostructure 33 2.2.2 Spontaneous Emission and Material Gain Calculation 34 2.2.3 QCL Rate Equations 36 2.2.4 QCL Modulation Response 38 2.3 Linewidth Enhancement Factor 39 2.3.1 Definition 39 2.3.2 Measurements Methods 40 2.3.3 α-Factor of QCLs 42 2.4 Detailed Study of a QCL Design 43 2.4.1 Fabrication of QCL Devices 43 2.4.2 QCL Internal Parameters 44 2.4.3 Laser Static Properties 45 2.4.4 QCL Gain Measurements 48 2.4.5 Intensity Noise Measurements 49 2.5 Conclusions 52 References 53 3 Optical Feedback in Interband Lasers 56 3.1 Analysis of the Optical Spectrum of a Laser Diode Under Optical Feedback 57 3.2 Analytical Approach of Optical Feedback 59 3.2.1 Rate Equations of a Laser Diode Under Optical Feedback 59 3.2.2 Feedback-Induced Frequency Shift 60 3.2.3 Threshold Reduction Due to Optical Feedback 61 3.2.4 Linewidth Evolution with Optical Feedback 61 3.2.5 Undulations on the L-I Curves 64 3.3 Dynamical Properties of a Laser Diode Under Optical Feedback 66 3.3.1 Dimensionless Rate Equations with Optical Feedback 66 3.3.2 Bifurcation Diagram Representing the Laser Dynamics 67 3.3.3 Influence of the Bias Current, the External Cavity Length and the α-factor on the Bifurcation Diagram 68 3.3.4 Phase Diagrams 70 3.3.5 Coherence Collapse and Chaos 70 3.3.6 Low Frequency Fluctuations 72 3.3.7 Extension to the Dynamics of a Class-A Laser Under Optical Feedback 75 3.3.8 Chaotic Laser Diodes and Applications 76 3.4 Conclusions 78 References 79 4 Impact of Optical Feedback on Quantum Cascade Lasers 83 4.1 Previous Studies 83 4.2 Experimental Setup 85 4.3 Numerical Model 87 4.4 Linewidth Enhancement Factor Measurement 88 4.4.1 Wavelength Shift with Optical Feedback 88 4.4.2 Self-mixing Interferometry 89 4.4.3 Gain Compression Coefficient 91 4.5 Influence of the Optical Feedback on the QCL L-I Characteristic Curves 94 4.5.1 Case of the DFB QCL 94 4.5.2 Case of the Fabry-Perot QCL 94 4.5.3 Optical Feedback from a Mid-infrared Fiber 95 4.6 Feedback Regimes in a Mid-infrared QCL 97 4.6.1 Optical Spectra of a QCL Under Optical Feedback 97 4.6.2 Feedback Cartography of the DFB QCL 98 4.7 Nonlinear Dynamics and Chaos in a QCL Under Optical Feedback 99 4.7.1 Time Series and Electrical Spectra 99 4.7.2 Low Frequency Fluctuations 101 4.7.3 Experimental Bifurcation Diagram 103 4.7.4 Numerical Bifurcation Diagram 104 4.7.5 Consequences of the Possible Chaotic Operation of a QCL 109 4.8 Conclusion 110 References 110 5 Beam Shaping in Broad-Area Quantum Cascade Lasers Using Optical Feedback 112 5.1 Motivations 112 5.2 Preliminary Study 114 5.2.1 Experimental Setup 114 5.2.2 Beam Shaping with Optical Feedback 115 5.2.3 Temporal Evolution with Optical Feedback 116 5.3 Case of a High-Performance 32 m-wide QCL 117 5.3.1 Design and Processing 117 5.3.2 Laser Performances 118 5.3.3 Beam Steering Effect 120 5.3.4 Modifications on the Optical Feedback Experimental Setup 121 5.3.5 Conventional Optical Feedback 122 5.3.6 Spatially-Filtered Optical Feedback 123 5.3.7 Feedback Response of a QCL with Multi-lobe Far-Field 123 5.3.8 Comparison with a 14μm-Wide Laser 125 5.4 Beam Steering Suppression with Optical Feedback 125 5.5 Conclusions 127 References 127 6 Impact of Optical Injection on Quantum Cascade Lasers 129 6.1 Impact of Optical Injection on Interband Laser Diodes 130 6.1.1 Locking Map 130 6.1.2 Improved Laser Properties in the Stable Locking Region 132 6.1.3 Instabilities and Chaos Outside the Stable Locking Region 134 6.2 Previous Studies of Optical Injection in Quantum Cascade Lasers 135 6.3 Numerical Analysis of Injection Locking in Quantum Cascade Lasers 137 6.3.1 Rate Equations Under Optical Injection 137 6.3.2 Analytical Model 138 6.3.3 Numerical Locking Map 141 6.4 Conclusions 146 References 146 7 Conclusions and Perspectives 149 References 152 Front Matter ....Pages i-xxiii Introduction (Louise Jumpertz)....Pages 1-8 Quantum Cascade Lasers: High Performance Mid-infrared Sources (Louise Jumpertz)....Pages 9-34 Optical Feedback in Interband Lasers (Louise Jumpertz)....Pages 35-61 Impact of Optical Feedback on Quantum Cascade Lasers (Louise Jumpertz)....Pages 63-91 Beam Shaping in Broad-Area Quantum Cascade Lasers Using Optical Feedback (Louise Jumpertz)....Pages 93-109 Impact of Optical Injection on Quantum Cascade Lasers (Louise Jumpertz)....Pages 111-130 Conclusions and Perspectives (Louise Jumpertz)....Pages 131-134