Multilayer equalizer for 2-channel OTDM-PAM-8 transmission system

We propose to utilize a multilayer equalizer (consisting of a demultiplexer based on two half-symbol-spaced feed-forward equalizers and a simplified symbol-spaced nonlinear multiple-input multiple-output equalizer) for a two-channel optical time-division multiplexed system. To operate the multiplexed system, it is necessary to compensate for the interference occurring during the multiplexing. The demultiplexer (in the first layer) makes the transmission performance insensitive to the sampling position, which enables the use of the symbol-spaced multiple-input multiple-output equalizer (in the second layer). This enables compensation for interference in the presence of a manufacturing imperfection of the multiplexer. Furthermore, this can enhance the performance of the nonlinear multiple-input multiple-output equalizer to lower the bit-error rate floor. For the second layer, we propose using a nonlinear multiple-input multiple-output equalizer with reduced complexity. We experimentally demonstrate the transmission of a 150-Gb/s optical time-division multiplexed signal based on eight-level pulse amplitude modulation over a 1.9-km standard single-mode fiber with a BER of < 10-3.