Comparison of the lasing modes of a microdisk and a microring

Microcavity lasers shaped as thin circular disks are famous for the ultra-low thresholds of their whispering-gallery (WG) modes. We considered a two-dimensional (2-D) model of such a laser in free space with a ring-like active region and compared the characteristics of its modes with the modes of an active microring, i.e. a similar disk with a concentric hole. The comparison showed that a microring has considerable rarefaction effect in terms of emission thresholds, accompanied by the blue-shift of emission spectra. If the ring becomes narrower than half-wavelength in material, then all lasing modes obtain catastrophically high thresholds.