All optical computing surfaces again!
Warning.
There is NO opportunity for large scale integration, the MOST IMPORTANT ASPECT in computing. This is because the de Broglie wavelength of the information carriers, typically 1.5um, is so HUGE.
Warning.
There is NO opportunity for large scale integration, the MOST IMPORTANT ASPECT in computing. This is because the de Broglie wavelength of the information carriers, typically 1.5um, is so HUGE.
The first is that light beams can cross paths without interfering with each other, allowing for a level of parallelism and density of signal paths without the concern of crosstalk/interference or shorting. Additionally, the information density of an optical signal is vastly higher than an electrical signal, and multiple optical signals can share the same pathways simultaneously. Also, energy usage is greatly reduced, so the constraints due to heat waste are much less.
Having said all that, the idea of optical circuits in a VLSI is still a very foreign and exotic concept for us, so it's hard to say how far we can take it if we invest at the level we have for electrical ICs. It's naive though to say it's not feasible due to some oversimplification of feature size limitations.
So there is a likely opportunity for large-scale integrated photonics, as long as you have enough parallelism.
Some potential benefits of optics include high data rate, parallel processing of multiple streams, transmission over longer distances, and lower heat dissipation.
What about vertically?
CMOS logic is still "mostly planar". With sufficiently low heat dissipation, you could make a cube and easily overcome the planar density problem.
The main challenge seems like it would be lithography cost for each of the many layers, but if the minimum feature size is 1.5um, there might be a clever way to make this work cheaply (DLP projection + gradual extrusion?)
But unfortunately, for small N, like the N = 2 bits here, the additional complexity of pure optical + quantum computing just doesn’t pay off!
If your gate gets 50x50x50 times bigger, you need some pretty extreme savings per area/volume of circuit if you want to reduce the per-gate usage. Can they save that much?
Light would reduce the time cost of distance, and increase the density of connections (optical signals can pass through each other) so this could actually work.
For classics optics. Exists superlens optics, which using metamaterials and monochromatic light source, and could "see" artifacts of size much less then wave length.