
Computing at the speed of light - jbrooksuk
http://unews.utah.edu/news_releases/silicon-photonics/
======
typon
What a terrible article, and it's on a University' official site. The headline
is highly misleading. Making a smaller beam-splitter has almost no effect on
making computers faster, let alone "at the speed of light".

This would be news-worthy and revolutionary if they somehow came up with a
photonic equivalent of a transistor. Something that doesn't exist yet, at
least in the traditional room-temperature equivalent, that's easy to integrate
on a chip.

All these passive photonic components, such as modulators, beam-splitters,
wave-guides and others are all just there to interface to the real work-
horses: the electronic transistors. And the best of these we have currently
have a maximum oscillation frequency of 1-2 THz (InP HEMTs). Anyway, saying
you can compute at the 'speed of light' is a meaningless statement. We measure
compute performance in cycles per second.

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EGreg
Better article: [http://mobile.extremetech.com/latest/221822-by-2020-you-
coul...](http://mobile.extremetech.com/latest/221822-by-2020-you-could-have-
an-exascale-speed-of-light-optical-computer-on-your-desk?origref=)

~~~
arxpoetica
Working link for those not on mobile:
[http://www.extremetech.com/extreme/187746-by-2020-you-
could-...](http://www.extremetech.com/extreme/187746-by-2020-you-could-have-
an-exascale-speed-of-light-optical-computer-on-your-desk)

~~~
basch
the mobile link was way better on desktop

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peter303
I saw this claim in the 1980s. Still waiting.

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Geee
More interesting would be a computer that moves at relativistic speeds or is
placed in a deep gravity well. At light speed or in a black hole the computer
would seem to make any computation instantly.

~~~
Retric
Works the other way, at relativistic speeds or in a deep gravity well time
slows down not speeds up.

~~~
Geee
Damn, you're right. So, I should leave my computer on Earth and make a long
trip at relativistic speed. When I come back, my computation would be much
further than if I had waited on Earth.

~~~
mikeash
Never fear, it works with a rotating black hole:
[http://en.wikipedia.org/wiki/Malament%E2%80%93Hogarth_spacet...](http://en.wikipedia.org/wiki/Malament%E2%80%93Hogarth_spacetime)

~~~
zxyzzxxx
_...observer falling into the black hole experiences an M-H event as they
cross the inner event horizon._

Too bad the observer can't share the result with anyone, and a couple of
moments later s|he expires.

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rbanffy
There is also this article (which is not about doing logic with light but
using light instead of electric current for moving information from one place
to another) from a week ago: [http://www.extremetech.com/extreme/205713-ibm-
announces-sili...](http://www.extremetech.com/extreme/205713-ibm-announces-
silicon-photonics-breakthrough-set-to-break-100gbs-barrier)

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steeve
I was under the impression that electrons moved at the speed of light, but
according to [1], they "only" move at 2200 km/s, which is less than 1% of the
speed of light (~300000 km/s).

Exciting times indeed.

[1]
[http://education.jlab.org/qa/electron_01.html](http://education.jlab.org/qa/electron_01.html)

~~~
bradleyland
This is a good example of asking the wrong question.

How fast does an electron move? 2200 km/s.

How fast does an electrical signal propagate from one end of a circuit to the
other? This is a much more relevant, but also more difficult, question. The
unit used to measure this performance is called Velocity Factor [1].
Unfortunately, I don't know what the VF would be within a modern
microprocessor, but in a wire, it varies from 50% to 99% of the speed of light
in a vacuum.

As is typical for mass media news, this story has been summarized in a way
that glosses over a lot of the detail.

Photonic computers have a very, very long way to go. Even this tiny beam beam
splitter is thousands of times larger than current transistors. Intel uses a
14 nanometer process for Broadwell. The University of Utah beam splitter is
2400 nanometers square. Let's not ignore the fact that a beam splitter and a
transistor aren't even close cousins. A beam splitter can't perform any logic.

All of this technology is still very much in the realm of basic science. A lot
of the assumptions about the speed improvements are based on napkin math
involving theoretical numbers. If anyone ought to know that the difference
between theory and reality is often muddied by the trip through the physical
world, it would be Photonics researchers. Fiber optic (probably the most
widespread application of Photonics research) performance is significantly
impacted by real-world factors. Far more so than electromagnetic mediums.

[1]:
[http://en.wikipedia.org/wiki/Velocity_factor#Typical_velocit...](http://en.wikipedia.org/wiki/Velocity_factor#Typical_velocity_factors)

~~~
stephengillie
> Photonic computers have a very, very long way to go. Even this tiny beam
> beam splitter is thousands of times larger than current transistors. Intel
> uses a 14 nanometer process for Broadwell.

The POC is a major milestone. Miniaturization will come. Don't forget that at
one time, we had to use flatbed trucks to move around 5MB of RAM.

~~~
bradleyland
Absolutely. A 2.4 micron beam splitter is a hell of an achievement. I don't
know what the next closest is in size, but the vast majority of beam splitters
I'm familiar with are measured in millimeters. I'm sure there are others doing
work on miniaturization, but 2.4 micron would seem like genuine landmark
progress.

What we need next is a practical photonic transistor at these scales!

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seanalltogether
What I don't understand about light computing is how to you use photons to do
work? EM radiation is great at carrying information, but it seems that you
need electricity to actually do the work of physically pushing gates and
transistors around. How do you actually replace the work load with light?

~~~
dougmany
Very tiny solar sails.

~~~
cloudsloth
Yeah!

Is that actually feasible?

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Phithagoras
The more informative original release from the University of Utah:
[http://unews.utah.edu/news_releases/silicon-
photonics/](http://unews.utah.edu/news_releases/silicon-photonics/)

~~~
sctb
Thanks, we updated the URL from [http://www.kutv.com/news/features/top-
stories/stories/Light-...](http://www.kutv.com/news/features/top-
stories/stories/Light-based-computers-in-development-to-be-millions-of-times-
faster-than-electronics-based-designs-133067.shtml).

