III-V microdisk/microring resonators and injection microlasers

Semiconductor whispering-gallery-mode (WGM) microresonators are promising candidates for creating compact, energy-efficient light sources (microlasers) for various applications owing to their small footprints, high Q factors, planar geometry, in-plane light emission, and high sensitivity to the environment. In this review we present the most recent advances in III-V microdisk/microring lasers. We briefly describe basic physics behind photonic WGM resonators and discuss different designs of III-V microdisk/microring lasers. We focus on the technological key points of the different approaches to realize efficient optical and carrier confinement in the laser cavity. Advantages and disadvantages of various types of the laser active region, i.e. quantum well (QW) and quantum dots, are discussed. We also report on successful fabrication of microlasers with gain medium of mixed dimensionality, so called QW-dots, which is promising for low-threshold, temperature insensitive and high output power operation. We summarized and systematically compare the characteristics of electrically driven microlasers. We address one major shortcoming for the circular WGM lasers, which is that the lasing emission is non-directional and non-homogeneous along the cavity rim. High quality factor of the resonator modes and circular symmetry lead to difficulties in obtaining the directional light output and in obtaining significant levels of the output optical power. We compared various techniques for realizing unidirectional emission or coupling to a waveguide. We also discuss high-speed direct modulation, which is another crucial characteristic for the microlasers. We also address energy consumption characteristics of the WGM microlasers under direct modulation and possibilities of energy-to-data ratio minimization. Finally, we summarize the prospects for the WGM lasers and their role in future applications in communications and sensing.