Gain-saturated spectral characteristics in a Raman-assisted fiber optical parametric amplifier.

We investigate the gain spectral characteristics in the course of saturation in a Raman-assisted fiber optical parametric amplifier (FOPA). It is experimentally observed that the saturated gain spectrum is modified with suppressed signal wavelength dependence as compared to a conventional FOPA. The gain at signal wavelengths on both farther and closer sides of the unsaturated gain peak from the pump saturates in a similar way. The modification of the saturated gain spectrum is explained by distributed nonlinear phase mismatch caused by the Raman effect.