[gorkish]

> Photonics and copper both travel at about the speed of light.

Just going to put this out there since it's totally non-obvious to a lot of armchair engineers, but this is not at all true. Velocity factor in most transmission lines (optical or electrical) is typically about 0.66c but varies depending on the material and the physical dimensions of the medium.

In very highspeed circuit design, (10s of ghz) both path length and velocity factor matching are considered when evaluating timing constraints for chipscale features.