ITTR, I will concur with your IMO that ADVA could be customer A, and a couple of tidbits may support this:

During the Sidoti talk yesterday, TM indicated that POET's "Customer A" made an announcement at OFC of the availability of new 100G product(s) matching the description of POET's 4 lambda 100G design, and to be available to their customers in the new year.  Of course, POET was never actually mentioned as being inside.

In a recent talk where SV reported out on OFC, he alludes to a situation where some of those attending ended up making the connection between the newly announced product and the POET platform's capabilities.

At OFC, ADVA announced upcoming availability of their new 100G CWDM4 and LR4 products, presumably to be released sometime early next year.

breadcrumbs perhaps, but compelling nontheless.