I would say optical clock coming in three to five years is a realistic expectation. That would be on-chip. Optics is an ideal way to do that. Usually, when you think about entry points, you look at the interconnection hierarchy starting with the edge of the system all the way down to the chip, and you figure it's going to be easier to enter in the high level than down. And then on to the chips themselves.
Integration is obviously the driving force.
We'll provide optical interconnection with dimensions comparable to current minimum feature sizes. Normally, you think of photons as being big. You can't shrink them down. But the size of a photon in a medium is lambda, the wavelength, divided by n, the refraction of the medium. Silicon has an index of refraction of 3.5, so you're shrinking it down by that size already.