To Lase or Not to Lase, That is The Question: Coherence, Dynamics & Modulation Response of Near-unity-beta Telecom-band Semiconductor Nanolasers
The pursuit for ideal integrated light sources that promise compact footprints, fast modulation and low energy consumption has led to the development of on-chip semiconductor nanostructure-based lasers. Their properties can be tailored to meet the demands of a broad range of applications including optical interconnects, quantum information processing, nonlinear microscopy and bio-/chemical sensing. Most current studies focus on proof-of-concept demonstrations of novel device designs, where the only evidence for lasing is provided by the conventional measurement of the output light intensity as a function of input intensity (LL-curve). While such a measurement is adequate for macroscopic devices ranging from large-scale solid-state lasers to commercial laser diodes on the order of a few hundred microns in size, it becomes less reliable for nanoscale lasers with high spontaneous emission factors, beta. Additionally, little has been done to examine the nonlinear dynamics of a single or multiple coupled nanolasers. Similarly, the fundamental response limit of a nanolaser subjected to small-signal modulation has seldom been investigated, especially experimentally. In light of such deficiency, we dedicate this thesis work to advance our understanding of these key aspects of nanostructure lasers. We first concentrate our attention on high-beta metal-clad photonic-mode nanolasers (MCPMNL). In Chapters 2 and 3, we present an experimental technique exploiting the second-order coherence function to assess the coherence and observe dynamical hysteresis of MCPMNLs. We show that while this technique is applicable to lasers with betas ranging from 10e-5 to unity, it is most beneficial for characterizing near-unity-beta nanolasers, when it supplants the LL-curve as one of the most reliable method to demonstrate lasing and identify the threshold. In Chapter 4, we demonstrate the first direct current modulation of an electrically pumped MCPMNL. Theoretical analyses indicate that the fundamental response limit near the lasing threshold for a MCPMNL is on the order of 10 GHz under pump modulation and 100 GHz under loss modulation. In the second part of this thesis, we present two collaborative efforts on other types of nanostructure lasers, including a topological laser engineered to possess arbitrarily large orbital angular momentum (Chapter 5) and two strongly coupled photonic crystal nanolasers exhibiting mode-correlation dynamics (Chapter 6).