Optical coupling of an active microdisk to a passive one: effect on the lasing thresholds of the whispering-gallery supermodes.

The lasing spectra and thresholds of a selectively pumped photonic molecule composed of two microdisks is investigated using effective index approximation and full-wave 2-D electromagnetic equations. The lasing eigenvalue problem formulation is used to find modal frequencies and threshold values of material gain. The influence of the optical coupling between active and passive microdisks on the lasing eigenvalues and directionalities of emission is studied. It is shown that for strong coupling the effect of making one of the resonators passive leads to the doubling of the threshold.