A good read.
"The 25.6-Tbits/s switch chips emerging around 2020 will need optical interfaces, authors of a book on silicon photonics predicted last year. On-board optics may be required as early as 2021, said networking veteran, Andreas Bechtolshiem , in a recent talk calling for an 800G Ethernet standard, perhaps the last to use discrete optical modules."
Full article here:
http://www.eetimes.com/document.asp?doc_id=1331512&page_number=1