Theory and experimental characterization of nanostructured lasers

This thesis explores the theory and experimentation of nanostructured lasers, with a focus on their potential for energy-efficient optical communication. In particular, it investigates Fano lasers, a class of microscopic lasers that exploit Fano interference, where discrete modes couple with a continuum, forming bound states in the continuum. These lasers offer promising features, including reduced quantum noise, robustness to optical feedback, and high-speed modulation capabilities. Theoretically, we reinterpret Fano lasers as dispersive laser cavities, where one mirror exhibits frequency-dependent reflectivity. We analyze their general stability properties and derive a novel characteristic equation linking dynamics directly to mirror dispersion. Two key instability mechanisms are identified: sidemode coupling and undamped relaxation oscillations due to dispersive feedback. While instabilities are often undesirable, they can be harnessed for useful functions such as self-pulsing and dual-mode lasing, with important applications in all-optical clock recovery and integrated signal modulation. Guided by our analysis, we propose two coupled-cavity Fano laser designs that exhibit dispersive self-Q-switching and dual-mode behavior. To further understand these systems, we develop a modal framework that tracks instantaneous modes, and derive reduced rate equations describing dynamics on the dominant mode’s center manifold. These insights inform the experimental realization of the proposed designs using nanobeam cavities, where lasing and related dynamic phenomena are demonstrated. Experimentally, we investigate the coupled-cavity Fano laser based on the nanobeam platform with embedded quantum dots. Lasing is demonstrated, and we also observe significant spectral broadening, indicating self-pulsing, as well as mode coupling and optical bistability. Besides Fano lasers, we demonstrate the generation of short optical pulses via nonHermitian coupling between two spatially separated nanolasers. This Q-switching-like effect arises from the abrupt modulation of the pump in one laser, while the other remains below threshold. Finally, we investigate the physics of quantum well lasers using k · p-theory to model band structure, gain, and spontaneous emission. The study sheds light on confinement effects and band mixing, as well as their influence on laser properties.