  We demonstrate that trapping of dispersive waves between two optical solitons
takes place when resonant scattering of the waves on the solitons leads to
nearly perfect reflections. The momentum transfer from the radiation to
solitons results in their mutual attraction and a subsequent collision. The
spectrum of the trapped radiation can either expand or shrink in the course of
the propagation, which is controlled by arranging either collision or
separation of the solitons.
