TM and TE directional modes of an optical microdisk resonator with a point scatterer

Dielectric microresonators are becoming key components for novel opto-electronic devices. Circular microresonators (microdisks) are natural candidates for lasing since some of their modes have extremely high Q-factor (low thresholds). In those modes, which are called whispering gallery modes, light circulates 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 emission which is due to rotational symmetry of the system. In contrast to usual procedure, where a geometric 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 point scatterer inside the microdisk itself. Numerical results show that both TM and TE highly directional modes are observed in the visible spectrum depending on the position of the scatterer. A simple geometric optic explanation of that dependence is given.