MODULATIONAL INSTABILITIES AND DARK SOLITONS IN A GENERALIZED NONLINEAR SCHRODINGER-EQUATION

The generalized nonlinear Schrodinger equation with the nonlinear term of a general form is considered. In particular cases this equation co vers a saturable nonlinearity as well as higher-order nonlinearities. Modulational instability is investigated, and the possibility of dark soliton propagation is analyzed. It is shown that in the small-amplitu de limit the generalized dark solitons are stable, and they are descri bed by the Korteweg-de Vries equation. The condition to create anti-da rk solitons is also formulated.