Evaluating SOA Nonlinearity Effects by High-Order Susceptibility on Constant Envelope Signals in WDM Systems

Nonlinearity effects, arising within a semiconductor optical amplifier (SOA), have been deeply investigated with particular interest for exploiting them in wavelength conversion. This application shrinks the research area to a precise scenario: a strong pump signal travels through the active medium simultaneously with a modulated signal to be converted. In this case, it is possible to neglect the spectral distribution of the optical power and phase relationship between propagating signals. SOAs have been also studied as line amplifiers for wavelength-division multiplexing (WDM) phase-modulated signals. Aim of this paper is to extend the propagation model in an SOA, in order to simulate nonlinearities occurring in the amplification of a WDM comb signal evaluating-wave mixing on constant envelope modulation schemes (differential phase-shift keying). This can be carried out due to an enhanced analytical model based on the optical field and medium interaction, overcoming the wide-used rate equation approach, which is based on the overall photons density.