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Comment by vturner | Hacker News Reader

Often wondered why we don't use light (photons) for computing. It seems we could control frequency and compute with it?

It's actually highly inefficient to do (general) computation with photons. In contrast to electrons, photons really don't like to interact so you need a lot of optical power to implement an optical transistor-like, this was studied by Prof. David Miller some time ago (doi:10.1038/nphoton.2009.240, I think this is the correct citation am on the phone right now). Like others said, the device proposed in the paper here is more like an analog computer (with ML they have really seen a revival, both in electronics and optics), for a specific "calculation" they can be vastly more efficient, but they can't do general computation. The device here relies on interference and the photodetectors provide the nonlinearity, people have been researching these type of devices for neural networks for quite a while.

I wondered similar things at various points. I’m still waiting for the Ga chips the guys at Intel said were right around the corner...in 1999. My rudimentary guess is tech or manufacturing just isn’t there.

I wrote some unpublished fiction once about a super computer that used light as the interconnect fabric between nodes/CPUs, where each core could talk to any other core with virtually no latency and high bandwidth. I guess it's never been used (widely) because it's easy enough to run copper.

Could you elaborate on the work? Did you write about unexpected implications of this technology?

Nothing that visionary or even self aware, but imagine a giant sphere, sealed with an inside vacuum and also coated on the inside with IC's connected via copper for power and basic communication but each IC also had a nodule/transceiver that could communicate with every other IC via the light spectrum, because every IC had line of sight to the others, all submerged in liquid nitrogen or some other coolant. The premise was a giant campus like a school that users would be able to carry near-dumb terminals around, like smartphones with very little power but if they needed computational power all they had to do to tap into the sphere, by being in visible range of receptacles all around the campus both inside and out. And the sphere could borrow processing power from unused devices if they were available. So light was the practical connection for users, but also used inside the sphere.

Copper is actually the faster way to interconnect electrical computers. https://www.arista.com/assets/data/pdf/Copper-Faster-Than-Fi...

For electrical computers connected via optics and vice versa there is also a latency cost to converting the signal types that makes doing so at <rack sized distances a painfully bad choice. Not to mention the cost & power associated with converting light to lasers and back. That being said any real world supercomputer bigger than 1 rack has a significant amount of optical interconnect as it's easier to get a coherent signal farther with optics at the same power.

There are not yet any good (cheap, reliable, composable) optical transistors.

As long as Moore's law keeps trucking along, there's no economic incentive to do so. This is similar to the explosion of Electron and other heavy technologies because there's no need to be efficient, or so some developers think. Of course, now that the law is slowing down, we might see more novel techniques, in both hardware and software design.

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