Ciena references data from the most recent 4Q18 Optical Application report in a blog post that outlines its opinions on how 400G is being deployed.

This month Cignal Ai updated its growth forecast for the coherent 400G DWDM market and provided the interesting graph below which shows how 400G will start to replace 100G and 200G deployments moving forward. The positive outlook represented in the graph is based on expected strong performance of 400G+ equipment across all distances and the expectation that the use of 400G ZR will expand to applications beyond data center interconnect (DCI).

The report also states that significant 400G growth will not begin until 2019, as Ciena is the only production supplier of this technology in 2018.