  The interaction of whispering gallery modes (WGM) of optical microresonators
with subwavelength imperfections has been studied both experimentally and
theoretically. This interaction is responsible for the formation of spectral
doublets in place of single resonance peaks, and for degrading of Q-factors of
the resonances. Within the currently accepted framework the spectral doublets
are explained as a result of degeneracy removal of clockwise and
counterclockwise WGMs due to their coupling caused by defect-induced
backscattering, while the degrading of the Q-factor is described
phenomenologically as an additional contribution to the overall decay rate of
WGM due to coupling between WGM and radiative modes. Here we show that the
existing understanding of this phenomenon is conceptually wrong and develop an
exact theory of WGM interaction with a single defect, which provides a unified
treatment for both aspects of this interaction explaining existing experiments
and predicting new phenomena.
