  We theoretically investigate light propagation in two periodically modulated
nonlinear waveguides with certain propagation constant detuning between two
guides. By slowly varying the amplitude of modulation, we can steer the light
to the desired output waveguide when equal amounts of lights are launched into
each waveguide. We also reveal that the light propagation dynamics depends
sensitively on the detuning between two guides. Our findings can be explained
qualitatively by means of adiabatic navigation of the extended nonlinear
Floquet states.
