  Mechanisms of whispering-gallery (WG) modes coupling in microdisk photonic
molecules (PMs) with slight and significant size mismatch are numerically
investigated. The results reveal two different scenarios of modes interaction
depending on the degree of this mismatch and offer new insight into how PM
parameters can be tuned to control and modify WG-modes wavelengths and
Q-factors. From a practical point of view, these findings offer a way to
fabricate PM microlaser structures that exhibit low thresholds and directional
emission, and at the same time are more tolerant to fabrication errors than
previously explored coupled-cavity structures composed of identical
microresonators.
