I. Introduction
The constantly increasing need for higher bit rates and longer optical transmission paths has led to alternative, more resilient to fiber losses and bandwidth efficient, modulation formats which exploit the phase of the optical field. Phase modulated signals exhibit a higher receiver sensitivity over conventional intensity modulation systems and suitability for multilevel signaling. The major impairment for phase modulation formats is the nonlinear phase noise produced by the accumulated amplitude noise of optical amplifiers and transferred to signal phase through fiber nonlinear effects, such as self-phase modulation (SPM) and cross-phase modulation (XPM). Till now, several techniques have been proposed for all-optical nonlinear phase noise suppression that are summarized in two basic categories; a) phase preserving amplitude limiters and b) phase sensitive parametric amplifiers.