I. Introduction
Analytical models for optical fiber transmission have been widely studied in the literature. These models are based on the equations that govern the optical field propagation: the nonlinear Schrödinger equation (NLSE) [1, Ch. 2] and its variants. The NLSE has no known exact solution for an arbitrary input waveform. One of the most efficient alternatives for approximated numerical solutions is the split step Fourier method (SSFM) [2], which simulates the effects of fiber propagation. On the other hand, to analyse these effects and design novel transceivers, analytical models are highly desirable.