Optical microdisk resonator with a small but finite size scatterer

Circular microresonators (microdisks) are natural can- didates for the realization of low-threshold miniature laser sources since some of their modes have extremely high Q-factors (low thresholds). In those modes, which are called whispering gallery modes, light cir- culates around the circumference of the disk trapped by total internal reflection. Although the microdisk cavities can provide ultra-low threshold lasing, their applicability faces the problem of isotropic light emis- sion which is due to the rotational symmetry of the system. Contrary to usual procedure, where a geo- metric deformation of the microdisk boundary is used to break the symmetry and, as a result, to achieve the output directionality, we propose a scenario inducing rotational symmetry breaking by placing a small but finite size circular scatterer inside the microdisk itself. We calculate positions of the new resonant modes and show that some of them possess clear emission direc- tionality while preserving high Q-factors.