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 dense wavelength-division-multiplexed (DWDM) systems with a 50-GHz channel spacing and multiple optical add-drop multiplexers (OADMs) is investigated. While the duobinary format is tolerant to passband narrowing, from concatenated filtering by the OADMs, it is very sensitive to the group-delay ripple (GDR) associated with this filtering. We show that GDR must be carefully controlled, e.g., by GDR compensation, before 40-Gb/s duobinary signals can be effectively used in DWDM systems originally designed for 10-Gb/s traffic.