Research On The Four-wave Mixing Crosstalk Characteristics Of Phase-sensitive Fiber Parametric Amplifiers

Phase sensitive fiber optical parametric amplifier(PS-FOPA)which based on four-wave mixing(FWM)process,is a kind of ultra-low noise optical amplifier.With 0dB quantum limited noise,this new type of optical amplifier can provide noiseless optical amplification.Moreover,PS-FOPA has the properties of high gain,large bandwidth,transparent to signal modulation rate and modulation format.It is potential in long-haul ultra-high-capacity optical fiber communication system.However,when wavelength division multiplexing(WDM)signal amplified by PS-FOPA,unnecessary FWM process will occur in the high nonlinear fiber inevitably,which produce additional frequency component in WDM signal bandwidth.This nonlinear crosstalk will limits the practical application of PS-FOPA in dense WDM system severely.In this paper,we investigated the FWM crosstalk characteristics of WDM amplification in PS-FOPA theoretically and experimentally.We proposed a scheme to suppress the FWM crosstalk and optimized the performance of the optical amplifier.The main research contents and results of this paper are as follows:(1)FWM crosstalk characteristics in WDM PS-FOPA system is studied experimentally and theoretically.We analyzed the process of FWM causing the crosstalk component in signal frequency band,and gave the approximate expression of FWM crosstalk.The results showed that FWM crosstalk increases significantly with the input signal power per channel,signal gain,nonlinear fiber length,signal channel number and other system parameters.FWM crosstalk of PS-FOPA and PI-FOPA is further compared experimentally,and the difference of crosstalk characteristics between PS-FOPA and PI-FOPA is explained through theoretical analysis and simulation.(2)Based on the above study on FWM crosstalk characteristics of PS-FOPA,we proposed to use hybrid PS-FOPA/EDFA scheme to suppress FWM crosstalk.We analyzed the relationship between the FWM crosstalk and noise characteristics of the hybrid PS-FOPA/EDFA and the PS-FOPA,and obtain the optimal gain allocation scheme of the hybrid amplifier system,which can realize the low-crosstalk low-noise optical amplification of PS-FOPA/EDFA.Furthermore,we discussed the experimental implementation of hybrid PS-FOPA /EDFA.(3)We have carried out some basic research on OFDM signal of PS-FOPA,including studied the influence mechanism of spectrum broadening of parametric pump on OFDM signal amplification and the suppression of nonlinear crosstalk.The results showed that the FWM effect between the pump after spectrum broadening and the signal optical carrier will generate redundant frequency components near the signal optical carrier.Because the frequency interval of the sub-carrier of OFDM signal is similar to the modulation frequency of the pump,these frequency components overlap with the sub-carrier of OFDM signal and produce signal crosstalk which referred to as phase modulation induced FWM(PMI-FWM)crosstalk.The magnitude of signal crosstalk is positively correlated with signal optical carrier power.In the experiment,we proposed to use carrier suppression modulation and coherent detection method to realize the suppression of PMI-FWM crosstalk for OFDM signals.These results provided useful guidance for the practical application of PS-FOPA in ultra-low noise amplification of multi-wavelength channels and multi-subcarriers with high spectral efficiency.