Reach extension of PAM4 signals in O-band transmission by application of alternate-mark-inversion

We improve the tolerance of O-band PAM4 transmission to nonlinearity by adopting an alternate-mark-inversion scheme. Improvements in receiver sensitivity are shown over both semiconductor optical amplifier and bismuth doped fibre amplifier equipped links, the greatest being a 4.4dB Q-factor improvement over 60km of SMF-28e.