III–V Semiconductor Whispering-Gallery Mode Micro-Cavity Lasers: Advances and Prospects

III-V semiconductor lasers are ubiquitous in modern optoelectronic devices, with applications ranging from telecommunication to general lighting. Among the different kinds of laser cavity designs, whispering-gallery mode (WGM) micro-cavity lasers boast outstanding optical performance due to advantages such as ultra-high Q-factor, compact mode volume, and narrow emission linewidth. Over the past decades, research in III-V WGM micro-cavity lasers has progressed rapidly in various aspects, including the fabrication techniques, emission outcoupling methods, and practical applications. In this paper, a comprehensive review is performed on the advances in these aspects. Although III-V WGM lasers are conventionally fabricated with top-down approaches, recent reports have demonstrated the potential of highly-scalable bottom-up methods in fabricating low-loss WGM lasers. Despite the strong optical confinement in III-V WGM cavities, various techniques have been developed to either outcouple WGM emission into waveguides or direct it into free-space with small beam divergence. Finally, recent developments in different applications of III-V WGM micro-cavity lasers are discussed. Other than serving as integrated photonic components, III-V WGM lasers have also displayed exciting potential in other applications such as label-free sensing and the study of cavity quantum electrodynamics (cQED).