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Comment by dannypgh | Hacker News Reader

It's definitely not a continuation of Moore's law as it has nothing to do with transistor density, but it may mean that the performance people expect from computers - which is why people are usually talking about Moore's law - may continue increasing.

I don't see how the wavelength is comparable to transistor size because as you switch to the optical realm, the benefit of information propagation at speeds near c (or c, if you're pulling a vacuum) means physical size doesn't matter as much. At 4Ghz you can move information 7.5cm in one cycle, and that's a pretty large distance compared to any integrated circuit I've ever seen.

Why is storage necessary? If you can move bits to optical gates and get a result back it seems to me like you can work around the fact that, in an electrical system, capacitance and heat (due to density achieved in the quest for minimizing capacitance) start to limit the computation you can do.

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I thought electric charge in conductors already moved very close to C? https://en.wikipedia.org/wiki/Speed_of_electricity

Exactly. If we're pedantic about it, a charge signal moves at the speed of light. But the signals are what computers use.

Only if you consider 70% or so to be close. There's some room for improvement over copper wires. Now, if there are any physicists here who want to jump in, I have a question about that. I heard waveguides are dispersive, would sending pulses of light through tiny channels slow it down as well?

But light in a dielectric medium also travels slower.

If n=1.3 -> v = c/1.3 = 77% of c

Some people working in optics say it works "at the speed of light." That's true of course ... but the speed is no different from using copper.

Unfortunately something like 0.7c is about the fastest speed of EM wave propagation in an optical waveguide or along a copper waveguide. Another comment here gives a slightly faster example with n=1.3, which is maybe achievable in some kind of polymer. Or in highly purified water, for what it's worth.

You can get a mild speedup, 40% or something, by moving to free space. But that is an unbelievable can of worms, taking all the signals out of the waveguides and somehow still getting 1B signals going to the right place. The 40% speedup doesn't remotely pay for giving up solid state waveguides.

"Dispersive" fortunately doesn't mean a meaningful slowdown. It just means that a transmitted bit will travel at a range of slightly different speeds. If it goes very far, the shape of the pulse will get messed up. But that's a problem people are already pretty good at solving.

Not a physicist, but you may want to look for 'hollow core fiber / photonic crystal fiber'.

Where some are said to reach up to 99.x % the speed of light in a vacuum.

Laser physicist here, did some work with PCF: Expensive as fuck, highly polarization dependent, almost impossible to splice.

Nonetheless it feels like at least every few months or even weeks a new announcement appears in pop-science sites like eurekalert and phys.org. Feels a little bit like the always around the corner next big battery tech.

Most fascinating thing i've read years ago they'd be the prime candidate for manufacturing in space, because real vacuum.

> Why is storage necessary?

Have you ever tried wiring any non-trivial logic without flip-flops? Say, a simple signal routing layer. Even the most basic bits of logic becomes much less efficient to downright impossible without storage.

You can use hybrid systems where, say, memory is conventional RAM but computation (maybe full cpu or submodule like apu) is done with photons. You can probably perform large numbers of concurrent operations by taking advantage of the wavelike properties of photons.

You can wave pipeline electrons too. It just very rapidly becomes an impossible design problem as the complexity of your design increases (and as the variation grows in significance with node shrinks)

Electrical signals in silicon are not that much slower than light in a vacuum and already signal propagation delay is a serious problem in CPUs.

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