Study On Gain And Noise Of TDM-pumped Fiber Raman Amplifier

With the development of next generation optical fiber communication network,the requirement of optical fiber communication system for channel capacity is higher and higher.Optical amplifier has become an indispensable amplifier device,which has attracted people's attention.Fiber Raman amplifier(FRA)has become a key technology in modern optical fiber communication because of its advantages of wide bandwidth,low noise and distributed amplification.It has been widely used in dense wavelength division multiplexing(DWDM)optical communication system.Gain characteristics and noise distribution have always been the research focus of FRA.Many schemes have been proposed to improve these two performances.This thesis focuses on the influence of multi wavelength time division multiplexing(TDM)pumping scheme and multi wavelength continuous wave(CW)pumping scheme on the gain performance and noise distribution of FRA.In this thesis,the development history and research status of FRA in China and abroad are briefly introduced,focusing on the principle of FRA and the principle of time division multiplexing pumping scheme.In addition,the transport model and related numerical solution of FRA used in this thesis are introduced.On this basis,the simulation model of the FRA using multi wavelength time division multiplexing(TDM)pumping scheme and multi wavelength continuous(CW)pumping scheme is designed,and the transport process of the FRA is shown in the time and space domain.Based on the simulation results,this paper focuses on:(1)The influence of pump period,pump duty cycle,pump sequence and input signal power on the receiver signal power of multi wavelength time division multiplexing(TDM)pumping scheme is studied.It is found that the signal power of the receiver is positively correlated with the input power.The average power of the receiver signal increases first and then decreases with the increase of pump period,and the peak difference increases gradually.At the same time,the period of signal power fluctuation at the receiver is positively correlated with the pump period.The change of pump sequence and pump duty cycle has influence on the average power and peak difference of the receiving signal,but does not change the periodicity of the signal.These rules will provide theoretical guidance for gain improvement and practical application of multi wavelength TDM pumping scheme.(2)The noise distribution of FRA pumped by multi wavelength TDM is studied.The accumulation process of amplifier spontaneous emission(ASE)noise,double Rayleigh backscattering(DRB)noise and FWM noise in time and space of fiber Raman amplification system in multi wavelength TDM pumping scheme is analyzed.It is found that ASE is the main noise source of TDM pumped FRA.Although four wave multiplexing(FWM)noise may exist in the actual operation process,it has little influence on the receiving signal and can be ignored.(3)The comparison of gain characteristics and noise distribution between TDM pump and CW pump scheme.It is found that the gain of TDM pump is higher than that of CW pump scheme,but the gain flatness of CW pump scheme is better than that of TDM pump.The effect of multi wavelength TDM in the same direction pump on ASE noise is better than that of multi wavelength continuous reverse pump,but it has the opposite effect on DRBs noise.(4)The quantitative evaluation method of fiber Raman amplification system for multi wavelength TDM pump scheme is presented.Based on the gain,noise and peak difference factors,the evaluation method of system performance is proposed.The feasibility of the evaluation standard is verified by changing the pump sequence.The results show that the quantitative evaluation scheme is feasible to some extent.By this method,the best pump sequence is selected successfully.