Can 40-Gb/s Duobinary Signals Be Carried over Transparent DWDM Systems with 50-GHz Channel Spacing?

The feasibility of transmitting 40-Gb/s optical duobinary signals over transparent DWDM systems with 50-GHz channel spacing and multiple optical add/drop multiplexers (OADMs) is investigated. While duobinary signal is tolerant to the passband narrowing due to the concatenated filtering by the OADMs, it is very sensitive to the group-delay ripple (GDR) associated with the filtering, making it difficult to pass through multiple conventional OADMs without severe penalty. It is pointed out that GDR has to be carefully controlled, e.g., by GDR compensation, before 40-Gb/s duobinary signals can be carried in DWDM systems originally designed for 10-Gb/s traffics.