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After 50 years of effort, researchers made silicon emit light

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Re: After 50 years of effort, researchers made silicon emit light

#81

Post by jpmattia »

> Modern transistors, which function as a computer’s brain cells, are only a few atoms long. If they are packed too tightly, that can cause all sorts of problems: electron traffic jams, overheating, and strange quantum effects. One solution is to replace some electronic circuits with optical connections that use photons instead of electrons to carry data around a chip.

Journalists need to be educated: Transmission lines are photonic, so silicon already has connections carrying data around using photons. As you would expect, those photons are traveling at the speed of light in the material.

If I were king, I would demand that every optical-silicon publication explicitly describe why their optical photons are more desirable than microwave photons that are already in widespread use.

Re: After 50 years of effort, researchers made silicon emit light

#82

Post by jacquesm »

miscPerson wrote: post #79
datenwolf wrote: post #50

Gaaah, please stop advertising optical computers as the technology that will overcome Moore's law. It makes no effing sense. Wavelength of the light emitted by these devices: ~4000nm Latest generation commodity CPU transistor structure size: 7nm Add to that that photons really don't like being trapped; you essentially need a delay line and optical amplifier to hold them indefinitely (that's essentially the core techn…

This is a tangent, but could you point me towards delay line + amplifier literature? Would be much appreciated.

That's how the very first computers worked:

https://www.computerhistory.org/storageengine/edsac-computer...

Not optical, but piezo electrical, usually with a crystal or air as the medium instead of mercury. Optical is much the same principle, a feedback loop incorporating the delay line, so the same bits get re-injected over and over again and can only be read out at specific points in time.

Re: After 50 years of effort, researchers made silicon emit light

#83

Post by jpmattia »

pieterk wrote: post #80

If anyone is interested in how this new material is made: it’s literally grown from scratch. Imagine a 3D printer at atom scale. But because the scale is so small, the nozzle has to deposit a gas. The magic is in making the individual gas molecules get to the right place. Layer by layer, to what theory predicted would be a light emitting configuration. Incredible achievement. https://www.nature.com/articles/s41586-02…

MOVPE is more of a self-assembly process than 3D printing, and it has been around for decades.

BTW It is worth noting from your link that the silicon is being grown on a GaAs substrate, so to be useful they would have to figure out how to grow the silicon wire on a silicon substrate. (GaAs already has many options for optical devices.)

Re: After 50 years of effort, researchers made silicon emit light

#84

Post by jl2718 »

So bad, had to stop reading.

>> cubic crystal lattice that allows electrons to move within the lattice under certain voltage conditions. But it doesn’t allow similar movement for photons, and that’s why light can’t move through silicon easily.

Uhhh.. not really. I’ll try to explain (forgive my ad-lib MatSci from 20 years ago). Efficient light generation is a matter of direct or indirect bandgap. A direct transition is one where the electron wave number is unchanged in dropping from the high to low energy state, so it can be completed with a single photon (light). An indirect transition fails conservation of energy and momentum with one photon, so it requires phonon (heat) interactions. Semiconductors have an energy gap between the highest few occupied state and the lowest few unoccupied states, and these are the only states that can exchange energy. Direct transitions generate mostly photons, so even if it gets absorbed, it will get re-emitted intact until it leaves the material. Indirect transitions means that phonons remove energy each time, so it all becomes heat. In normal conditions, Indirect materials are more transparent, although direct materials can become transparent by population inversion, which is when there are more electrons in the high-energy states then the low-energy states for the bandwidth of the photons being generated. Then any photon generated is more likely to generate more photons on its way out (stimulated emission) than to be absorbed. This is what you want. Okay I’ll stop now, but there are tricks that you can use to get this behavior in silicon, an indirect-bandgap material, which is the topic of the article.

Re: After 50 years of effort, researchers made silicon emit light

#85

Post by hinkley »

jacquesm wrote: post #82
miscPerson wrote: post #79

Earlier quoted context omitted.

This is a tangent, but could you point me towards delay line + amplifier literature? Would be much appreciated.

That's how the very first computers worked: https://www.computerhistory.org/storageengine/edsac-computer... Not optical, but piezo electrical, usually with a crystal or air as the medium instead of mercury. Optical is much the same principle, a feedback loop incorporating the delay line, so the same bits get re-injected over and over again and can only be read out at specific points in time.

I thought the mercury delay lines were the craziest thing I’d heard about in computer evolution until I learned about using a cathode ray tube as memory.

Re: After 50 years of effort, researchers made silicon emit light

#86

Post by econcon »

You can get light out of anything.

All you need to do is shoot it with a photon bean, and the when material can no longer absorb the photons you send at it, it will begin releasing them as reflection. But the one you are shooting in aren't the same ones that are coming out.

Re: After 50 years of effort, researchers made silicon emit light

#87

Post by LargoLasskhyfv »

whatshisface wrote: post #65
gibybo wrote: post #62

Earlier quoted context omitted.

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

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?

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.

Re: After 50 years of effort, researchers made silicon emit light

#88

Post by twomoretime »

lopsidedBrain wrote: post #60
dannypgh wrote: post #55

Earlier quoted context omitted.

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…

> 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.

Re: After 50 years of effort, researchers made silicon emit light

#89

Post by ip26 »

twomoretime wrote: post #88
lopsidedBrain wrote: post #60

Earlier quoted context omitted.

> 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)

Re: After 50 years of effort, researchers made silicon emit light

#90

Post by jacquesm »

hinkley wrote: post #85
jacquesm wrote: post #82

Earlier quoted context omitted.

That's how the very first computers worked: https://www.computerhistory.org/storageengine/edsac-computer... Not optical, but piezo electrical, usually with a crystal or air as the medium instead of mercury. Optical is much the same principle, a feedback loop incorporating the delay line, so the same bits get re-injected over and over again and can only be read out at specific points in time.

I thought the mercury delay lines were the craziest thing I’d heard about in computer evolution until I learned about using a cathode ray tube as memory.

In a way that is a delay line too, the phosphor decay time allows you to read out the bits a bit later than you put them in. The big advantage is that it is theoretically random access.
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