
After 50 years of effort, researchers made silicon emit light - john_alan
https://www.wired.com/story/after-50-years-of-effort-researchers-made-silicon-emit-light/
======
datenwolf
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 technology my whole PhD thesis centers around), it makes
them a really impractical thing to store bits with. Things with a rest mass
can be stored easily, though. Things like, say, electrons!

~~~
dannypgh
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.

~~~
gibybo
I thought electric charge in conductors already moved very close to C?
[https://en.wikipedia.org/wiki/Speed_of_electricity](https://en.wikipedia.org/wiki/Speed_of_electricity)

~~~
whatshisface
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?

~~~
LargoLasskhyfv
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.

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

~~~
LargoLasskhyfv
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.

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armada651
It's kind of fitting that this was done in Eindhoven, a city that formed
around the Philips light bulb factory.

It's a place that celebrates a history of making stuff glow.

~~~
donnellycc
I graduated from TU/e and in my experience their applied physics department,
specifically nanomaterials like this are very well funded and attract a lot of
international talent.

Eindhoven likes light! And....making bridges out of beer crates:
[https://www.ed.nl/default/tu-e-studenten-vestigen-nieuw-
reco...](https://www.ed.nl/default/tu-e-studenten-vestigen-nieuw-record-met-
bierkrattenbrug-video-foto-s~a0720318/)

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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.

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xt00
Super cool -- one challenge will be that in order to live on the hot
processors of today, these emitters will need to still work at around 400K --
the good news is that these appear to still work well at around 300K -- but it
sounds like these go to nearly no bandgap at higher temperatures and shift
into the infrafred. But yea, pretty awesome stuff..

~~~
01100011
Wouldn't infrared be acceptable for data transmission?

~~~
GordonS
Not sure how applicable it is, but the IrDA (Infrared Data Association)
protocol tops out at only 16Mbps.

~~~
layoutIfNeeded
False.

>GigaIR: 512 Mbit/s – 1 Gbit/s, NRZI, 2-ASK, 4-ASK, 8b/10b

[https://en.wikipedia.org/wiki/Infrared_Data_Association](https://en.wikipedia.org/wiki/Infrared_Data_Association)

~~~
fulafel
GigaIR seems to be vapourware from 2008 that died since.

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pieterk
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/s41586-020-2150-y/figures/6](https://www.nature.com/articles/s41586-020-2150-y/figures/6)

~~~
jpmattia
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.)

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cybert00th
Really impressed they stuck at it, by the sounds of it there's still a lot of
work to do. Hopefully it won't be another 50 years before we see it adopted at
scale.

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RaoulP
Is the breakthrough here about emission or transmission? Or is the physics for
these two connected? It's not clear to me, between the title and the article.

Secondly, could using a "photonic" memory bus bring RAM access speeds close to
cache speeds, or is the transmission distance/time not the main issue there?

~~~
Sheppy96
Transmission time isn’t really the main issue, it’s more about the work
required to get a memory request through the levels of the hierarchy to DRAM
and back. Probing each level of cache, propagating through the miss queues,
translation (maybe with TLB miss), waiting for the DRAM controller, etc.

~~~
adwn
What? That doesn't make sense. If cache probing would be the cause for DRAM
accesses being slow, we wouldn't need caches. We would just access DRAM
directly!

It's the other way around: DRAM accesses are slow, that's why we need caches.

> _translation (maybe with TLB miss)_

In most architectures, the caches are physically addressed, so TLB lookups
occur _before_ even L1 cache access. Successful TLB lookups are extremely
fast! And you can't skip the TLB, even if you don't have any data caches.

~~~
MrBuddyCasino
> In most architectures, the caches are physically addressed, so TLB lookups
> occur before even L1 cache access.

So to see if a memory location is contained in a cache line, a TLB lookup is
needed to first get the physical address? I wouldn't have expected this, can
you expand on why this is the case?

~~~
dooglius
See Linus Torvalds' thesis, section 4.3.3 "The case against virtual data
caches":
[https://www.cs.helsinki.fi/u/kutvonen/index_files/linus.pdf](https://www.cs.helsinki.fi/u/kutvonen/index_files/linus.pdf)

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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.

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jonplackett
On a scale of zero to really big deal. How much of a big deal is this?

~~~
The_rationalist
Photonic can only be up to 20% faster... And I'm talking about a fully
photonic cpu, not an hybrid one that has a light/electricity translation cost.

~~~
gridlockd
> Photonic can only be up to 20% faster...

How did you come up with that number? The speed of travel? That's not really
the main bottleneck in current computer architectures, at least not yet.

Using photons would enable quite different architectures that we haven't even
conceived of yet.

------
baybal2
Silicon photodiodes and LEDs are in the infrared range, so they still can be
considered light emitting

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ctack
Really not sure this is the correct way to think about it, but if the silicon
is now transparent and parts of it are emitting light, how is the focus
limited / controlled ie. how does a receiver know from emitter it should be
receiving from?

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wffurr
How long until isolinear optical chips, then?

[https://memory-alpha.fandom.com/wiki/Isolinear_chip](https://memory-
alpha.fandom.com/wiki/Isolinear_chip)

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thatguy27
Anybody else annoyed by this being written up as if the research was just
published?

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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.

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anthk
Good. This means less heat, and a much faster transmission.

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mattjoyce
Title : "After 50 Years of Effort".... 1st Para : "NEARLY FIFTY YEARS ago,
Gordon Moore..."

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knolax
> Modern transistors, which function as a computer’s brain cells

Who's the target audience for this analogy? If you understand what a brain
cell is then you probably know what a transistor is too. I would bet that more
people know what a transistor is than what a brain cell is.

~~~
capableweb
You don't need to know the details of a brain cell to get the analogy. If I
say "transistor" to my mom, she wouldn't be able to tell me what it is. If I
say "It's like the brain cells for the computer", she would probably
understand that "Ah, so a computer has many transistors that helps it think",
which seems good enough for an article with a broad audience.

> I would bet that more people know what a transistor is than what a brain
> cell is

I'm happy to take you up on that bet, but it depends on what bubble you ask.
In San Francisco/Silicon Valley, that's probably true, but outside any high-
tech bubbles, more people know that we have brain cells in our heads, than we
have transistors in our computers, I'm fairly sure.

~~~
Someone
I would take that bet, too. If you say “transistor” to non-technical people
over 50 or so, they more likely would think of small portable radios
([https://en.m.wikipedia.org/wiki/Transistor_radio](https://en.m.wikipedia.org/wiki/Transistor_radio)).
To them, and many others, computers don’t have transistors, they have chips.

They _might_ know the transistor replaced vacuum tubes, but I doubt many would
be able to tell what function either had, or be able to point out the
transistors inside such a radio.

~~~
pbhjpbhj
Is that a USA/North America thing, based on calling radio sets "transistor
radios"?

Here in the UK we had "the wireless", and I'm confident that my parents - late
70s - who were the generation of first domestic computer ownership in the UK
would associate "transistor" primarily with computers.

~~~
romwell
Definitely not just a USA thing, "transistor" also meant "transistor radio" in
Russian back in the day.

(E.g. this song from 1982: [https://learnsongs.ru/song/dinamik-na-plyazhe-
pleshchet-voln...](https://learnsongs.ru/song/dinamik-na-plyazhe-pleshchet-
volna-68477))

~~~
neeleshs
Same in India!

