Colored-Noise Suppressed Decision Feed-Forward Equalizer for Passive Optical Networks

Driven by bandwidth-hungry applications, 50G passive optical network (PON) has been standardized towards the upstream line rates of 25Gb/$s$ (asymmetric mode) or 50Gbps (symmetric mode). For the asymmetric mode of 50G PON, the legacy 10G-class components with limited bandwidth can be reused with digital signal processing to achieve the upstream line rate of 25Gb/s and maintain cost efficiency. To deal with the limited bandwidth-induced inter-symbol interference (ISI), the feed-forward equalizer (FFE) is the most commonly used. However, the in-band noise will be colored and amplified after using FFE, which will degrade the performance. This paper proposes the decision FFE (DFFE) to deal with the limited bandwidth-induced ISI and suppress the colored noise. The experimental results of the 25Gb/s on-off keying using 10G-class components show approximately 0.5dB improvement in receiver sensitivity at 20 % soft-decision forward error correction limit after using DFFE compared to FFE.