Nonlinearity Compensation in a Fiber-Optic Link by Optical Phase Conjugation

This article is intended as a guide to the techniques for nonlinearity compensation in a fiber-optic communication link based on optical phase conjugation. In the first part, the basics of the phase conjugation process are illustrated from both a mathematical and physical point of view. Then, the more commonly used devices for optical phase conjugation are described, with particular attention to the devices based on periodically poled lithium niobate waveguides. Subsequently, the applications of optical phase conjugation to the nonlinearity compensation of amplitude-modulated and phase-modulated signals are analyzed.