ABSTRACT
The whispering gallery at Saint Paul's Cathedral, London, is known to be able to convey whispers tens of meters away along the gallery wall. The first theory-based investigation of optical whispering gallery microresonators (WGMs) was published as early as 1939, while the experimental demonstration was pioneered by several research groups in the late 1970s to early 1980s. Silicon nitride (SiN), whose high nonlinear properties have remained a focus of research into nonlinear optics, is used in fabricating whispering gallery microcavities. An exotic type of microcavity is the bottleneck resonator, which is fabricated by a heat-and-pull process and which hosts whispering gallery modes that are displaced toward and away from the bottlenecks. A relevant topic concerning whispering gallery mode resonators with optical gain is second-harmonic light generation. The chapter provides a brief overview on some fundamental concepts regarding whispering gallery microcavities, materials used for cavity fabrication, as well as various types of cavities under investigation.
