All-Optical Time-Extended OCDM-PAM4 for 200 Gbps/λ O-Band Multi-Span Transmission

This paper presents an all-optical time-extended optical code division multiplexing (TE-OCDM) system using two different optical en/decoders (E/Ds). The proposed system configuration alleviates the rigorous requirement for transmitter specifications in TE-OCDM systems. We numerically evaluate the use of PAM-4 with TE-OCDM for the first time by optimizing chip period to reduce inter-symbol interference (ISI). We utilize an analytical model and simulations to investigate the bit error rate (BER) in back-to-back scenario as a function of extinction ratio (ER) and total power contrast ratio (PCR). The fiber simulation with inline amplifications shows that 8 TE-OCDM PAM-4 signals at 12.5 Gbaud using 1274 nm could reach up to $8\times 30$ km. The total bit rate is equivalent to 200 Gbps (8 TE-OCDM users $\times 12.5$ Gbaud $\times 2$ bits/symbol) per wavelength. Further analysis of the scalability of TE-OCDM over the entire O-band through the optical E/D spectral periodicity, suggests that the feasible total bit rate that can be achieved is approximately 3 Tbps.