It's not because of Mercury.

We've had this discussion here awhile back and we learned the Mercury doesn't have a trademark, dead or alive.

What seems to be happening (among other things) is that POET is having trouble convincing the examiner that POET isn't just a mere description of what it is, rather than a name.

I think it would be like if Coca-Cola wanted to call themselves "F-Disc" (fizzy-diabetes-inducing-sugar-concoction). It's merely a description of what they offer, but it's also what Pepsi offers, and others aswell. It means that another company with a process to make flat chips combining optics and electronics would also be "POET".

I'm not 100% certain of this since I'm not a lawyer, but it's what I gathered by reading the response from USPTO on their site

http://tsdr.uspto.gov/documentviewer?caseId=sn86465512&docId=OOA20150916170052#docIndex=0&page=1

and here's a discussion about a similar case (which was referred in POET's non-final)

http://thettablog.blogspot.com/2012/09/precedential-no-29-ttab-affirms-2e1-and.html