  We theoretically study transmission in nanowaveguide coupled to high-quality
plasmon resonances for which the metal loss is overcompensated by gain. The
on-resonance transmission can vary widely from lower than --20dB to higher than
20dB for a range of gain coefficient. A reversible transition between the
high-quality amplification and the suppression can be induced by a quite small
change of gain coefficient for a moderately increased distance between the
waveguide and the resonator. It is expected that in practice a small change of
gain coefficient can be made by flexibly controlling pumping rate or utilizing
nonlinear gain. Additionally, based on the frequency-dependant model for
gain-transition susceptibility, it is shown that the wide variation of the
on-resonance transmission can also be observed for defferent detuning of the
gain-transition line-center. Such a widely controllable on-resonance
transmission is promising for applications such as well-controlled lumped
amplification of surface plasmon-polariton as well as plasmonic switching.
