Characterization of Polarization Pulling in Fiber Optical Parametric Amplifiers

In fiber optical parametric amplifiers (FOPAs), the output states of polarization (SOPs) of both the signal and the idler are affected by the pump SOP through the polarization pulling effect. We proposed a normalized model to characterize the general dynamics of polarization pulling in degenerated pump FOPAs. By using this model, we determined the relationship between the output degree of polarization (DOP) and the gain of the FOPAs over three orders of magnitude changes in polarization-mode dispersion (PMD) coefficient. We demonstrated numerically that when fibers with typical PMD coefficients are used, the output signals of the FOPAs can achieve higher DOP than those of co-propagating fiber Raman amplifiers, which depends on whether the parametric gain is sufficiently large to compensate the PMD-induced phase mismatch. We also found that for FOPAs using different types of fibers with moderate PMD coefficients, this DOP-gain relationship exhibits highly similar behaviors. We thus adopted a set of modified empirical formulas to analyze this relationship. This formula can also describe the relationship between the output DOP and the conversion efficiency of the idler. The results indicate that in all cases studied, FOPAs achieve much stronger polarization pulling to the idlers than the signals.