All-optical soliton switching for the asymmetric fiber couplers.

Coupled nonlinear Schrödinger (CNLS) equations for the fiber couplers with asymmetric self-phase modulation (SPM) and cross-phase modulation (XPM) are studied. With symbolic computation, one- and two-soliton solutions are obtained for the constant- and variable-coefficient CNLS equations. Switching dynamics of the solitons is discussed, and effects of the second-order group-velocity dispersion β, SPM coefficient σ, XPM coefficient σ and Kerr nonlinear intensity γ on the all-optical switching properties are studied, while other coefficients in those equations are seen not to affect the all-optical switching properties. For the constant-coefficient CNLS equations, we find that | β| is proportional to the optical switching speed, and the optical extinction ratios increase with the decrease of σ/ σ and increase of | β| and γ. A numerical simulation by the split-step Fourier and Runge-Kutta methods is presented on the constant-coefficient CNLS equations to analyse the stability of the one- and two-solitons with the random initial perturbations. For the variable-coefficient CNLS equations, effects of σ/ σ, β( z) = a e and γ( z) = a e on the optical switching are analyzed (where a, a and b are all constants, and z gives the direction of propagation in the fiber couplers): optical switching speed increases with the increase of | a| and decrease of | b|, and optical extinction ratios increase with the increase of | a| and decrease of σ/ σ and | a|. [ABSTRACT FROM AUTHOR]