Nonlinearity Tolerance of RZ-AMI Format in 42.7-Gb/s Long Haul Transmission Over Standard SMF Spans

We compare 42.7-Gb/s return-to-zero alternate mark inversion (RZ-AMI) and return-to-zero on-off keying (RZ-OOK) formats in a recirculating loop transmission experiment over 24x80-km standard single-mode fiber (SMF) spans. It is found that RZ-AMI is more tolerant to fiber nonlinearity, in good agreement with theoretical and numerical predictions.