50-km C-Band Transmission of 50-Gb/s PAM4 Using 10-G EML and Complexity-Reduced Adaptive Equalization

In this paper, we experimentally demonstrate the transmission of 50-Gb/s four-level pulse-amplitude modulation (PAM4) signal over 50-km standard single mode fiber (SSMF) in C-band using electroabsorption modulated laser and PIN/APD detector with 8.5/6 GHz bandwidth. A simplified Volterra-DFE filter is proposed, which reduces the required tap number by ∼70% compared with traditional DFE and Volterra filtering. Experimental results show that by using 86-tap equalization, a sensitivity of –15 and –14 dBm can be achieved at the FEC limit of 1 × 10⁻³ in back to back (BtB) and 50-km SSMF transmission cases. In addition, by replacing the PIN-TIA with a 10-Gb/s APD-ROSA for detection, the sensitivity can be further increased by 5.5 and 3 dB for BtB and 50-km SSMF transmission cases, respectively.