Finite-dimensional description of nonlinear pulse propagation in optical-fiber couplers with applications to soliton switching

We have developed a general formalism able to describe nonlinear pulse propagation in multimode optical fibers or waveguide couplers by means of a finite number of parameters, which are functions of the traveled distance. These parameters possess a direct physical meaning and can be interpreted, for a wide class of time-dependent interaction phenomena, as conjugate variables of a suitable Hamiltonian. The accuracy and the importance of the method are discussed with reference to a specific example of bimodal optical propagation, involving soliton switching and soliton instabilities.