Many-body effects and quantum-optical mode coupling in semiconductor lasers

Semiconductor lasers are invaluable tools for technological progress. They are indispensable for applications in optical communications, integrated photonic circuits, entanglement generation, quantum computing and sensing. This work develops a comprehensive quantum-optical semiconductor laser theory based on an equation of motion approach, capturing a broad spectrum of laser phenomena. A key focus is the linewidth behavior of singlemode quantum-well lasers. Deviations from the Schawlow-Townes behavior, particularly in micro- and nanolasers, are investigated. Many-body effects, including Coulomb interactions and electron-phonon coupling, significantly influence laser characteristics and alter the gain spectrum. Furthermore, the work extends the laser theory to multimode operation, identifying critical mode coupling mechanisms and introducing the concept of a “coherent phase” as a criterion for distinguishing between quantum and classical regimes. It is discussed that spontaneous emission disrupts phase coherence, while conventional lasers maintain it above the threshold. The research also explores the role of electron scattering in multimode lasing, demonstrating its major impact on laser characteristics. Additionally, the developed multimode laser theory is used to investigate mode locking in single-section quantum-dot lasers. Established theories for mode locking are based on a classical description of the light field, whereas here a quantum-optical theory is developed. Quantum fluctuations and relaxation dynamics are shown to play a crucial role for pulse generation. An analytical lower limit for the width of the beat-note spectrum is derived, with future work suggested to explore intensity-dependent effects on mode locking stability. These findings contribute to the theoretical foundation necessary for advancements in on-chip quantum computing, quantum communication, and integrated photonics.