Design and fabrication of single-mode tunable lasers for regrowth-free monolithically integrated photonic circuits

In this communication age, the bandwidth requirements are increasing exponentially with the development of more and more data-intensive services, from high-definition video streaming and cloud-based computing to the Internet of Things and machine-to-machine communication. This rapid expansion is powered by a rapidly growing fibre-based optical communication network. This growth, both in geographical extension and density of terminals, results in a large-scale need for the photonic components that are at the core of the optical communication network. In order to satisfy the demand, photonics industries need to increase their production capabilities and adopt more efficient fabrication processes. Streamlining the fabrication implies the removal of slow or costly processes. In the case of the photonics fabrication, epitaxial regrowth and advanced lithography steps are slow and expensive parts of the fabrication, and are one of the first targets for streamlining the process. In addition to reducing the cost of the fabrication itself, the integrated electronics approach can be a source of inspiration with the monolithic integration of multiple photonic components fabricated at the same time to create highly complex circuits while limiting the fabrication complexity. Focusing on a component at the core of photonic circuits: the tunable single-mode laser, this work is a contribution to the development of components that can be fabricated without requiring any regrowth or advanced lithography. Based on multi-cavity geometries enabled by multimode interference couplers and on a cleave-free approach to facilitate integration, a portfolio of tunable lasers is presented, showing tuning ranges of up to 51nm in the C and L optical windows, and side-mode suppression ratio levels of up to 35dB. Inspired by integrated electronics, proofs of concept for monolithically integrated electroabsorption modulated lasers and comb sources are presented, showing up to 19.5dB static absorption ratios for the modulated lasers, and a 4GHz optical comb tuned over a 28nm discrete tuning range. These results validate the proposed lasers as suitable candidates for the development of monolithically integrated photonic circuits where the fabrication complexity was kept minimal, making them attractive devices for the large-scale, streamlined production processes necessary to meet the increasing need for photonic components