A comprehensive study on XPM- and SRS-induced noise in cascaded IM-DD optical fiber transmission systems

A comprehensive study of XPM- and SRS-induced crosstalk noise evolution as well as their interaction along lossy, nonlinear dispersive fiber in a cascaded IM-DD system is performed analytically and numerically. XPM-induced intensity noise (XPMN) comes mainly from few adjacent channels, featuring in higher frequency and higher noise power per contributing channel; while SRS-induced intensity noise (SRSN) comes mainly from all the distant channels, featuring in lower frequency and lower noise power per contributing channel. Interaction between XPMN and SRSN depends on the relative wavelength location between pump and probe as well as dispersion management scheme, and may add either constructively or destructively. SRSN may even exceed XPMN in some cases. In a system with complete dispersion compensation in each span, XPMN, SRSN, and their interaction are all proportional to the square of span number. In dispersion-managed systems, SRSN can be enhanced significantly by resonance effect between fiber spans. On the other hand, XPMN can be markedly suppressed by dispersion management, due mainly to much weaker phase-to-intensity noise conversion through residual dispersion.