Optical Amplified 40-Gbps Symmetrical TDM-PON Using 10-Gbps Optics and DSP

We proposed and demonstrated a symmetrical 40-Gbps time division multiplexed passive optical network (TDM-PON) using low-cost 10-Gbps optical components in the optical network unit, optical amplification at the optical line terminal (OLT), and digital signal processing (DSP), based on four-level pulsed amplitude (PAM-4) modulation in the downstream and electrical duobinary (EDB) detection in the upstream. The use of 10-Gbps components in combination with DSP allows us to increase the serial bitrate beyond 10 Gbps for TDM-PON in a more cost-effective way. The reduced signal-to-noise ratio and the reduced dispersion tolerance by going to the higher rate were investigated for PAM-4 and EDB and optimized using DSP for PON applications. 33-dB power budget and 0–10 km range has been achieved for continuous-mode PAM-4 downstream transfer, and 29-dB power budget and 0–5 km range has been demonstrated for burst-mode EDB upstream transmission at 1537 nm. DSP, in the form of feedforward equalization and decision feedback equalization, compensated for the limited system bandwidth and significantly improved the 10-Gbps class receiver performance for 40 Gbps. Erbium doped fiber amplifiers (EDFAs) were used in the OLT as both booster and preamplifier. DSP techniques were applied to help recover the burst-mode upstream signal and effectively compensate for the amplitude transient effect from EDFAs.