How could you make a 2nm optics cable? The wavelengths are two orders of magnitude larger than that.

Not even remotely an expert on chip design, but deep learning dataflow is a lot more predictable and linear than what a CPU or even a GPU doing actual graphics needs to do. Speed of light latency is probably not an issue since the relevant distances are not one side of the die to the other but rather the distance between adjacent components.

I don’t think the size of silicon transistors has anything to do with this. There is no direct comparison. So they will prob bigger but no one cares.

Photonic integrated circuits are almost as old as regular integrated circuits.