Role of Coherent Systems in the Next DCI Generation

Coherent transmission has been the standard for fiber optic communications for 100 Gbps rates and higher at distances of 40 km and above for more than a decade. In this paper, we review the continuing role of coherent systems for data center interconnect (DCI) networks at 400 Gbps, 800 Gbps and higher rates, including 1.6 and 3.2 Tbps. We review market factors driving demand for coherent DCI transmission solutions today and over the next five years, with attention to the transition to an IP over DWDM (IPoDWDM) architecture. Implications for small form factor, multi-vendor interoperable, low power consumption transceivers are investigated. We discuss in detail the technical challenges for compact pluggable transceivers operating at symbol rates of 120 Gbaud and above, including speed, interconnect, packaging and power consumption.