PT-Symmetry in Colloidal Quantum Dot Microdisk Lasers with Engineered Notches

Whispering gallery mode resonators are susceptible to parasitic splitting of clockwise and counterclockwise modes due to the sensitivity of optical modes to perturbations of the circular resonator boundary. This makes them useful devices for optical sensing and allow for evanescently coupling of modes of different resonators. We have studied laser mode behavior when a notch is engineered into the boundary of circular microdisk resonator based on colloidal quantum dots. We found substantive reduction of the parasitic mode splitting and enhanced emission directionality for resonators with by tuning the size of the notch. We also investigated the effects of Parity-Time (PT) symmetry in evanescently coupled microdisk pairs with variation of the gain and loss induced by the optical pump. We demonstrate that the exceptional point behavior of these systems can be controlled by the size of the engineered notch.