This "partner" for sure is not a normal "customer". There must be a very trustful relation behind all this.

Most of us agreed in the past that this technology (POET as well as now the optical interposer) is too important to be monopolized. The buyer of DL (with all its well-trained staff!) is not purchasing the IP of POET but finally will have a very deep insight into the technology and even the tiny tweaks and tricks of the optical interposer platform.

I thought it would be the single most important issue to protect the IP of POET: That the interposer would be manufactured by POET inside their DL-fab and then shipped out to the final customers made much sense to me. 

So selling this Fab means POET would endanger to lose this IP?
Don't we see behind all this the dream of Ajit Manocha and the Fab 2.0? https://www.youtube.com/watch?v=ZbVVD6seIGs

For me, it is clear that POET soon will again be a fabless company still having access to the labs of DL (Possibly also somewhere in GB?) I see a change of 15% that Silterra is the buyer but 80% that this is all about GF. And I am not in fear about this cooperation, but see this as a huge opportunity to stay fabless with a strong partner.