Phase-controlled optical switching and slow- and weak-light solitons in a coherent molecular system with permanent dipole moments

We investigate the linear and nonlinear light pulse propagations in a three-level λ-type molecular system with permanent dipole moments via electromagnetically induced transparency (EIT). We find that EIT characters in such a system depend strongly on the phase of control field, based on which a phase-controlled optical switch can be designed. We show that the Kerr nonlinearity of the system can be largely enhanced due to the controlfield-induced quantum interference effect. We derive a nonlinear Schrödinger equation for the evolution of the probe-field envelope and demonstrate that it is possible to generate stable slow- and weak-light solitons in the system.