Amplifier-less transmission of 56Gbit/s PAM4 over 60km using 25Gbps EML and APD

In this paper, we experimentally demonstrated 56Gbit/s PAM4 signal optical amplifier-less transmissions over a record distance 60km using 25Gbps EML and APD. Compared to PD-based receiver, improvements of 7dB and 50% in terms of receiver sensitivity and transmission distance were achieved.