Polarization-dependent parametric and Raman processes in a birefringent optical fiber

The generation of new frequencies by the parametric four-photon mixing process, stimulated Raman processes, and subsequent stimulated mixing processes, all of which arise from the third-order nonlinearity in a single-mode birefringent fiber, is reported. It is observed that different processes are dominant for different input pump polarization angles with respect to the birefringence axes of the fiber. By examining the evolution of the nonlinear output spectra at various input pump power levels for different polarization angles, the pump-polarization-dependent third-order nonlinear processes are studied in detail. The effect of the birefringence-compensated group-velocity matching between the pump and parametric frequencies of different polarizations results in effective nonlinear interactions over long distances for the picosecond pulses