This is why POET is building both LR4 and FR4 which effectively covers all data center reach requirements  in the most economical way possible.

This line should probably have read: "This  is  why  POET's Tier 1 company (the US customer) is  paying POET to  build both LR4 and FR4 400G optical  engines".

Multiplexing different wavelength onto single fiber using CMOS processes is  going to  be an industry leading product. And market intelegence indicates that only POET can achieve this. This is ultimately the lowest cost solution for higher data rates but as Suresh says it is very hard. It is  why people are building other standards that do  not integrate CWDM...because they can't do  it.