Nonlinear Effects Mitigation for a PDM-16QAM 224 Gb/s Transmission systems using DBP and MLSE

High order modulation nonlinear effects has been appointed as the main limitation in coherent optical fiber transmission. Many different approaches has been investigated to cope with nonlinear effects in optical systems and the most studied method for coherent systems is the digital back-propagation algorithm. MLSE methods have also been effective in combating nonlinear impairments; however it has only been implemented for 112 Gb/s QPSK systems. In this paper, we perform, for the first time, a maximum likelihood sequence estimator (MLSE) in the context of an experimental PDM-16QAM transmission and compare the result with Digital Back-propagation equalization. Also, the use of a combination of both methods is proposed, which increases the distance reached in over 40%.