Electronic Equalization of Intrachannel Nonlinearities

Abstract

Intra-channel nonlinearities are the major nonlinear penalties in 40 Gb/s and above high-speed transmission. In this paper electronic equalization of intra-channel nonlinearities is studied. IntroductionElectronic equalization has been an effective technique to overcome the distortion caused by inter-symbol interference (ISI). Recently it has been applied in high bit-rate (10 Gb/s) optical transmission systems and most of the studies have concentrated on compensation of chromatic dispersion (CD), polarization mode dispersion (PMD) and multi-mode dispersion (MMD) [1][2][3]. Various implementations of equalization technique have been investigated include both Viterbi equalizers based on maximum likelihood sequence estimation (MLSE) and analog equalizers such as the feed-forward equalizer (FFE) and the decision-feedback equalizer (DFE). With increased interest for higher data rate systems, we believe the application of equalization at 40 Gb/s will soon become commercially important. In high-speed transmission (at 40 Gb/s and above) the major nonlinear penalties come from intra-channel interactions [4,5], such as intra-channel four-wave-mixing (IFWM) and intra-channel crossphase modulation (IXPM), which cause different ISI pattern with dispersion. The IXPM causes the timing jitter and the IFWM causes ghost pulses in the empty bit slot. Because of shorter pulse width, it's not suitable to compensate chromatic dispersion with electronic equalizer in such systems, especially in long-haul ones. In this paper, unlike current focus on dispersion compensation, we will investigate the capability of electronic equalization for intra-channel nonlinearity.