Investigation of Raman-Assisted Crosstalk Reduction in Multi-Wavelength Fiber Optical Parametric Amplification

Suppression of four-wave mixing (FWM) crosstalk during multi-wavelength amplification in a Raman-assisted fiber optical parametric amplifier (FOPA) is investigated theoretically and experimentally. The principle of crosstalk reduction by using a backward Raman pump is revealed by analytical expressions and verified by simulations. The crosstalk reduction is attributed to the unique power evolution of the signals caused by the monotonically increasing parametric pump power in the Raman-assisted FOPA. We obtain more than 7-dB reduction in FWM crosstalk initiated from both degenerate-FWM and nondegenerate-FWM processes in the Raman-assisted FOPA, as compared to a conventional FOPA with equivalent signal gain. The experimental results show excellent agreement with the simulations. We also discuss the effects of signal channel number and the powers of the parametric pump and the Raman pump on the FWM crosstalk. The simulation results indicate that under the same level of signal gain, the amount of crosstalk reduction can be increased by using a stronger Raman pump associated with a weaker parametric pump.