Raman-induced limitation of gain flatness in broadband fiber-optical parametric amplifier

Abstract

Raman effect brings the inevitable limitation of gain flatness in the fiber-optical parametric amplifier even if the phase-matched condition is well satisfied. Phase-matched gain is modulated by the real part of Raman susceptibility especially when it is on the anti-Stokes side. The real part mainly determines the gain profile and limits the flat-gain bandwidth to be less than 180 nm. An asymmetric modulated gain spectrum appears due to the assistance of the imaginary part on the Stokes side. Simulation results also show that the single- and dual-pump configurations have different gain amplitude modulation factors induced by Raman.