This paper analyzes the Four Wave Mixing(FWM) phenomenon between pump and noise in the application of Fiber Raman Amplifiers(FRA) in Non-Zero Dispersion Shifted Fibers(NZ-DSF) and deduces the position where the fourth beam of light appears and proves it in experiments.On this basis
it suggests that when FRA are applied in NZ-DSF
the pump wavelength should be far away from the zero dispersion shift point