SOAs Nonlinearities and Their Applications for Next Generation of Optical Networks

Semiconductor optical amplifiers (SOAs) have attracted a lot of interest because of their application potential in the field of optical communications. Their use has been envisaged in different applications in the access, core and metropolitan networks. Particularly, they have been envisioned for all-optical signal processing tasks at very high bit rates that cannot be handled by electronics, such as wavelength conversion, signal regeneration, optical switching as well as logic operations. To implement such all-optical processing features, the phenomena mostly used are: cross gain modulation (XGM), cross phase modulation (XPM), four-wave mixing (FWM) and cross polarization modulation (XPolM). The aim of the present work is to present a qualitative and an exhaustive study of the nonlinear effects in the SOA structure and their applications to achieve important functions for next generation of optical networks. These phenomena are exploited in high speed optical communication networks to assure high speed devices and various applications, such as: wavelength converters in WDM networks, all-optical switches, optical logic gates, etc. Particularly, we focus on analyzing the impact of variation of intrinsic and extrinsic parameters of the SOA on the polarization rotation effect in the structure. This nonlinear behavior is investigated referring to numerical simulations using a numerical model that we developed based on the Coupled Mode Theory (CMT) and the formalism of Stokes. Consequently, it is shown that the azimuth and the ellipticity parameters of the output signal undergo changes according to injection conditions, i.e. by varying the operating wavelength, the input polarization state, the bias current, the confinement factor and obviously the SOA length, which plays an important role in the gain dynamics of the structure. We will show that the obtained results by the developed model are consistent with those obtained following the experimental measurements that have been carried out in free space. In addition, an investigation of the impact of nonlinear effects on the SOA behavior in linear operating and saturation regimes will be reported. Their exploitation feasibility for applications in high bit rate optical networks are therefore discussed. Hence, the impact of variation of the SOA parameters on the saturation phenomena is analyzed by our numerical simulations. It was shown that high saturation power feature, which is particularly required in wavelength division multiplexing (WDM) applications to avoid crosstalk arising from gain saturation effects, can be achieved by choosing moderate values of the operating parameters. Moreover, we will address one of the essential processes to consider in SOAs