Phase-controlled stable solitons in nonlinear fibers

Bright and grey coupled solitons with complex envelopes are obtained as exact solutions of the system describing doped optical nonlinear fibers. The solitons formed are found to be free of amplitude and phase instabilities during their evolution, leading to the realization of stable soliton propagation. The phase of the input solitons plays a crucial role in the formation of tanh–sech paired pulses. This soliton is not supported in a two-level atomic medium and is exclusive to the Λ system.