Nonlinear Amplification Of Noise In Optical Communication System And Its Influence On Pulse Breakup

Noise nonlinear amplification, in optical communication system, can reduce the SNR (Signal to Noise Ratio) of system, and increase its BER (Bit Error Rate), resulting in degradation of system performance. Noise nonlinear amplification caused by MI (modulational instability) is one of mechanisms for pulse breakup. In this paper, a model of optical pulse transmission in single-mode fiber (SMF) is established in the presence of noise, and the mechanisms for breakup of chirped pulse with different durations are analyzed through numerically solving the theoretic model, and special attention is given to the effect of noise nonlinear amplification on the chirped pulse breakup. The results are listed as following:Mechanisms for breakup of pulses with different durations and effect of noise on non-chirped pulse breakup are simulated using Spit-step Fourier Method (SSFM), respectively. It is found that, in the absence of noise, for both of short and intermediate pulse, the pulse breakup starts from the pulse collapse due to high-order soliton compression, but the long pulse breakup is caused by noise nonlinear amplification resulting from MI. However, the noise can make the intermediate pulse break up due to MI instead of high-order soliton compression, and the mechanism of short and long pulse breakup are still high-order soliton compression and MI, respectively, even in the presence of noise.Great attention is given to the effect of initial chirp on the pulse breakup. It is found that, the effect of initial chirp on pulse breakup depends on mechanisms of pulse breakup both in the absence of noise and in the presence of noise. For the pulses which break up due to high-order soliton compression, the positive and negative initial chirp can enhance and slow down the process of pulse breakup, respectively. However, for the pulses which break up due to MI, the initial chirp has little influence on the process of pulse breakup. Moreover, the process of short pulse breakup is related to the strength of negative initial chirp, and the short pulse experiences no pulse compression, and breaks up from the top of the pulse during the initial stage of pulse breakup when strong negative initial chirp is applied.