In microdisk cavities, whispering-gallery optical modes are confined
by total internal reflection at the boundary of the disk. The small
mode volumes and the ultralow losses of the modes offer a high potential
for several applications, such as low-threshold lasing. The uniform
in-plane light emission from an ideal disk with circular cross section,
however, is a significant drawback. In this chapter we review the recent
progress in microdisk design for unidirectional light emission from
modes with low losses. We compare and discuss the pros and cons of
various approaches. One important aspect is the ray-wave correspondence
in such deformed microdisks.
