We developed an analytical model for the statistics of polarization-dependent gain (PDG) in both copumped and counterpumped fiber Raman amplifiers (FRAs). The validity of this model was confirmed by using experimental data and numerical simulations. The results show that the PDG in a counterpumped FRA cannot be neglected since it is only about 3 times smaller than that in a copumped FRA. Using the proposed model, we also evaluated the effects of various parameters on the PDG including the wavelength difference between the signal and pump,degree-of-polarization (DOP) of pump laser, polarization-mode dispersion,and fiber loss at the pump wavelength. In addition, the proposed model was used to analyze the requirement of the DOP of pump for the suppression of PDG within 1 dB.
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