  We put forward the concept of resonant, Rabi-like flopping and adiabatic
transitions between confined light modes in properly modulated multimode
waveguides. The phenomenon is shown to take place in both, the linear and the
nonlinear regimes. In addition, we find that the mode transitions occur not
only in simple geometries, but also in complex confining multimode structures.
The phenomenon is analogous to the familiar stimulated state transitions that
occur in multilevel quantum systems.
