Nonlinear Evolution of Amplitude and Phase Modulated Signals and Performance Evaluation of Single-channel Systems in Long Haul Optical Fiber Links

Abstract

In this work we numerically study the signal evolution in long haul links in presence of nonlinear Kerr effect, chromatic dispersion and ASE of the optical amplifiers, and the performance of long-haul IM-DD and PSK coherent systems is also evaluated. Propagation in condition of low and high chromatic dispersion is analyzed taking into account also the chromatic dispersion fluctuations. In the first propagation regime the signal presents a large spectral broadening due to the nonlinear interaction between ASE and signal. Conditions for transmission of NRZ intensity and phase modulated signals are found, even though the IM-DD systems present better performance. In the second propagation regime the nonlinear Kerr effect can compensate the degradation induced by the chromatic dispersion both for amplitude and phase modulated signals in the anomalous dispersion region. Also in this regime the IM-DD systems present better performance than the PSK ones and soliton propagation, included in this regime, allows us to obtain the best conditions for signal transmission. A performance comparison among optical systems, considering the two propagation regimes, shows that the best performance is obtained by means of soliton IM-DD systems in the case of very long distances (> 6000 km) and by means of conventional IM-DD systems operating at the zero dispersion wavelength in the case of long distances (< 6000 km). The zero dispersion wavelength condition can be practically obtained considering links with a fluctuating GVD presenting an average value equal to zero.