Dynamic Range Improvement in Fiber Optical Parametric Amplifier With Raman Pumping

We experimentally show that the 1 dB compression point at the gain peak of a fiber optical parametric amplifier (FOPA) can be improved by 4.2 dB when it is assisted with a backward Raman pump to deliver an unsaturated gain of ~25 dB. We derive an efficient numerical model to describe gain saturation in a Raman-assisted FOPA (RA-FOPA). By scrutinizing the evolution of the optical fields, we find that the phase relation among the signal, the pump, and the idler can alleviate gain saturation in the RA-FOPA, instead of accelerating the saturation as in a conventional FOPA. Enhanced linear amplification is also demonstrated with a Nyquist-shaped 16-QAM signal, where the maximum signal power into the RA-FOPA can be 2.2 dB higher than that into the conventional FOPA within a 0.5 dB Q-factor penalty. This letter shows that the RA-FOPA has a superior dynamic range for linear operation, facilitating high-performance amplification for higher-order modulation formats.