Coherent vector π pulse in optical amplifiers

We obtain an exact linearly polarized vector solitary solution for the amplification of an optical pulse with a time width short compared with both population and polarization decay time. This dissipative soliton results from the balance between the gain from inverted resonant two-level atoms and the linear loss of the host material. We suppose that the excited state of the active centers is degenerate on the projection of the angular momentum, with a symmetric state of inversion. Quite remarkably, we find that after the passing of the pulse, the atomic medium does not return to the ground state, and a finite Zeeman coherence is generated. Numerical simulations demonstrate the stability of vector π solitons with an arbitrary state of elliptical polarization in the presence of both linear birefringence and group-velocity dispersion of the host material.