Intrapulse Four-Wave Mixing and Four-Component Ultraslow Optical Solitons

The nonlinear propagation of a probe pulse in a M-type five-level atomic system is investigated under the condition of electromagnetically induced transparency. As for a long probe pulse, its dispersion effect can be neglected, and the four-wave mixing process and the energy exchange can occur among the four components within the probe pulse with different polarization directions and different side-bands. In contrast, as for a short probe pulse, the dispersion effect must be considered, and a novel kind of four-component ultraslow optical soliton occurs among these four components. In addition, the input power for the generation of such soliton is at micro-watt level, which is much lower than that needed for the generation of the vector solitons in fibers.