Photonic integrated circuit (PIC), the technology that integrates multiple photonic components into a functional circuit on a single chip, is one of the key technologies for high-speed data communication and telecommunication. However, the integration density of PICs has been limited by the physical dimensions of on-chip light sources. Thus far, on-chip lasers with a micro-scale device footprint and low power consumption remain elusive due to various fabrication challenges. While micro-cavity lasers fabricated by conventional top-down etching suffer from scattering losses due to sidewall roughness, traditional bottom-up laser fabrication approach such as the vapour-liquid-solid growth of nanowire lasers faces challenges including limited scalability, poor fabrication reproducibility, and potential metallic contamination.

Here, we demonstrate a bottom-up approach to fabricate uniform arrays of III-V micro-ring lasers as potential on-chip light sources. In my talk, three different aspects of the bottom-up III-V micro-ring lasers will be covered. In the first part of the talk, I will be discussing the growth of InP laser cavities with a uniform ring-like morphology by utilising a shape engineering technique via selective area epitaxy. The micro-ring cavities are terminated by sidewalls consisting of high-quality crystal facets, which can act as optical mirrors to form a whispering-gallery mode (WGM) cavity with a high Q-factor. 

In the second part of the talk, I will be discussing the direct incorporation of an InAsP/InP multi-quantum well (MQW) gain medium into the bottom-up micro-ring cavities. With an atomic-resolution transmission electron microscopy analysis, we will look into the detailed growth mechanism of the MQW gain medium. The MQW micro-ring cavities show low-threshold lasing at room-temperature, with tunable emission wavelengths in the telecommunication O-band. More importantly, with a high-throughput laser characterisation technique, we have demonstrated a remarkable > 80% fabrication yield in over a thousand micro-ring lasers – a chip-scale fabrication process.

Finally, in the third part of the talk, I will present results on the fabrication of a directional laser based on an optically-coupled InP micro-ring/nanowire system. While conventional WGM lasers are known to have poor emission directionality, in this work we have achieved vertical emission by coupling the micro-ring laser emission into a vertical nanowire grown at the ring centre, which acts as a directional antenna. Vertical laser emissions with strong far-field directivities in the coupled systems have been confirmed using a Fourier imaging technique.