Nonlinear Electrical Predistortion and Equalization for the Coherent Optical Communication System

One of major issues of the advanced optical communication system is the signal distortion caused by fiber nonlinearity. Both predistorters and equalizers have been used for nonlinearity compensation and electrical compensation has become a popular choice among optical communication engineers in recent years. However, to the best of the authors´ knowledge, no comparative study about electrical equalizers and predistorters has been conducted for optical communication systems. Using a coherent optical orthogonal frequency division multiplexing (CO-OFDM) system as a test system, we investigated the performance of electrical p th-order inverse Volterra predistorters and equalizers. Our research results show that both the equalizer and the predistorter can compensate for the nonlinearity of the CO-OFDM system. The major difference between the predistorter and the equalizer is that the predistorter regulates the input power; therefore, the performance of the CO-OFDM system with a predistorter is independent over a wide range of the laser launch power. The results presented in this paper can lead to a better understanding of electrical equalization and predistortion techniques for optical communication systems.