Thanks Derek,
Some simples figure to explain it:
And now, remenber that December 2015 article in Nature journal, see the optical amplifiers before the receivers ?!? (sorry for image clarity)
The other questions that was debated about this article, was that we don't know if the laser in an on of off-chip solution and it is a VCSEL (low-powered) of not?
http://www.nature.com/nature/journal/v528/n7583/abs/nature16454.html