Stability criterion of coupled soliton states

By operator theory, we prove that the stability of coupled fundamental soliton solutions of two coupled nonlinear Schrodinger equations is determined by dP/d beta criterion (with P the power or energy and beta the propagation constant). Examples of the application of the stability criterion to the coupled fundamental soliton states in nonlinear couplers, birefringent fibers, and birefringent nonlinear planar waveguides are given. The predictions from the analytical stability criterion are consistent with numerical results.