Light leaks a little at every interface, and coupling is where CPO's optical losses concentrate, an invisible ceiling on yield and serviceability. Doubling V-groove density, edge vs. grating coupling, passive vs. active alignment: this unglamorous layer is where volume-production gaps open up.

CPO decks spend 90% of their time on EIC-PIC stacking, but the first question in data center ops is: can you replace the fiber? Four companies, four approaches and three optical interfaces are competing, and whoever ships first may set the de facto standard.