Propagation properties of dark solitons

We numerically study the initial-value problem of the nonlinear Schrödinger equation in the normal-dispersion regime of an optical fiber. A nonchirped hyperbolic tangent input pulse having arbitrary amplitude is found to evolve into a primary dark soliton having a constant amplitude and speed. The effect of the input amplitude is to alter the pulse width of the primary dark soliton. In addition, a set of secondary dark solitons of smaller amplitude moving away from the primary pulse is also generated. It is also shown that nonlinear dark pulses in optical fibers are more stable than bright pulses with respect to loss and noise.

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