FJ,

POET has stated they are targeting DR and FR "reaches" for 400G. So that means they are committed to PAM-4 optical modulation. Additionally, at least the FR requires forward error correction. So that is good in the sense that they are not just committing to the "easy" stuff.

One question is can POET support coherent? I can't see where they said they can or cannot.

To be considered coherent modulation means that you are tracking phase, in this case the phase of the lightwave itself. The long reach ZR spec requires this. I can't see anywhere POET has ever mentioned doing this version. As it is long reach this is probably a lower demand higher margin product.

FR spec...

http://www.100glambda.com/specifications/download/2-specifications/1-400g-fr4-technical-spec-d1p0

rogue