PULSE GENERATION IN BIREFRINGENT OPTICAL FIBERS BY 4-WAVE-MIXING AND RAMAN-SCATTERING

Pulse generation in birefringent fibers by four-wave mixing in the pre sence of Raman scattering is theoretically modeled by a set of coupled nonlinear Schrodinger equations that are solved numerically. We discu ss phase matching in the positive group-velocity dispersion regime for the split-pump configuration, which places the parametric frequency s hift within the Raman band, and derive the combined initial gain. It: is found that for shorter fiber lengths the symmetry-breaking roles of Raman-Stokes gain and Raman-anti-Stokes loss is balanced by four-wave mixing, resulting in a common effective power, gain for both componen ts. The importance of the relative phase of the four participating pul ses as a switching parameter for the direction of the energy flow is d emonstrated. It is further shown that, as a result of pulse walk-off, Raman scattering becomes the dominant process for longer fiber lengths . Theoretical results are compared with experimental cross-correlation pulse shapes.