  Interference patterns associated with soliton-soliton interaction are
investigated in detail. We find that the temporal and spatial interference
patterns exhibit quite different characteristics. The period of the spatial
interference pattern is determined by the relative velocity of the solitons,
and the temporal pattern behavior is determined by the peak amplitudes and the
kinetic energy of the solitons. Analytical expressions for the periods of the
interference patterns are obtained. A method for classifying the nonlinearity
of many nonlinear systems is proposed. As an example, we discuss possibilities
to observe these properties of solitons in a nonlinear planar waveguide.
