I know when silicon photonics were brand new, they had a big limitation because they only had designs that fired out of the plane of the chip, not across it. That limits you to interconnects and not cross-chip signaling. And since for a CPU you need a heat sink on top that means you have to fire down, toward the motherboard.

Also it turns out the speed of light in glass is not that impressive. So encoding and decoding at the ends eats up the speed advantage. That’s my impression as to why a lot of high profile articles on optical logic came out shortly thereafter. What if we just keep it as light for longer?