
Engineers demo first processor that uses light for ultrafast communications - signa11
http://news.berkeley.edu/2015/12/23/electronic-photonic-microprocessor-chip/
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yelnatz
> The photonic I/O on the chip is also energy-efficient, using only 1.3
> picojoules per bit, equivalent to consuming 1.3 watts of power to transmit a
> terabit of data per second. In the experiments, the data was sent to a
> receiver 10 meters away and back.

They mentioned this, but didn't compare it to classic electrical chips.

Does anyone know what we have now?

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exDM69
> Does anyone know what we have now?

I can't quote exact figures but to give a ballpark figure, we're talking about
~5 picojoules per bit at a distance of less than 10 millimeters. This is on a
modern (20 nm) SoC.

So we're talking about a pretty significant improvement in power consumption
and communication distances. A modern chip running at 2-4 GHz requires several
clock cycles for a bit to reach from one corner of the silicon to another.
It's becoming a major hurdle to think about when designing chips.

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thecopy
Does this imply that it will be possible to increase the clock-speed 5/1.3=3.8
times and still be able to cool the CPU with basic air-cooling?

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typon
No it doesn't. This does not affect clock frequency on a single CPU. This
would improve bandwidth and latency in I/O with off chip circuitry such as
memory or co-processors (like GPU).

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madengr
Why would it improve latency? At most it would reduce it by half; i.e. Free-
space propagation vs traces buried in FR4.

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typon
It wouldn't and you're correct. I don't know why I wrote that. Sorry!

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pjc50
Does anyone have a link to the actual paper?

Key point which people may get confused on: this is light for inter-chip
communication, not light-based computation. The achievement is miniaturizing
the transceivers, making them with a standard-ish IC process (Germanium isn't
entirely standard, but very useful), and presumably finding some way to
connect optical fiber in the same way that gold wires are currently bonded to
IC pads.

There are probably a lot of sub-advancements in photonics involved as well.

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jamessb
The actual paper is:
[http://www.nature.com/nature/journal/v528/n7583/pdf/nature16...](http://www.nature.com/nature/journal/v528/n7583/pdf/nature16454.pdf)

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evook
On the 8th ISP and Carrier Lunch in Frankfurt 2013, I heard a talk from
CompassEOS thematizing optical processing chips for a new Generation of
routers. In my opionion It's kind of click baiting to talk about the "first"
processor utilizing light to improve connection speed when I had similiar
technology already in my hands back in 2013.

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ZenoArrow
Two questions:

1\. Had they demonstrated the optical processing chips could be manufactured
with existing processes by building a working chip?

2\. Did the chip(s) in question only route networking signals or were they
capable of more general purpose computing?

There's been plenty of research into integrating optical connects into a
silicon chip, but this is the first general purpose chip I know of which has
done so with existing manufacturing methods, and to me both of those are
important milestones.

EDIT: Looks like IBM managed to beat the Berkeley team, appears they got
something very similar working in 2012:

[http://researcher.watson.ibm.com/researcher/view_group.php?i...](http://researcher.watson.ibm.com/researcher/view_group.php?id=2757)

~~~
evook
> 1\. Had they demonstrated the optical processing chips could be manufactured
> with existing processes by building a working chip?

They had a working setup for demonstration, also we were allowed to hold the
chips, also you wouldn't invite the biggest german networking companies for
lunch without having something to sell. So basically yes.

> 2\. Did the chip(s) in question only route networking signals or were they
> capable of more general purpose computing?

Those chips were limited to route networking signals chip to chip or chip to
backlane. If I remember right CompassOS choosed networking to get production
ready as fast a possible, propably also on the interessents of their investors
who were mainly network focused (e.g. Cisco, Comcast and T-Venture).

Edit: So Berkeley is again selling already developed Innovations as their
accomplishment. “This is a milestone. It’s the first processor that can use
light to communicate with the external world,”

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ZenoArrow
I see, thanks for the info about the Compass chip.

As for Berkeley, yes it appears their PR department is telling lies. Even
though it's promising work, I do wish they could've announced it in a
different way. Silicon photonics is an interesting field, I don't need to be
told about world firsts to find it interesting.

~~~
evook
It's super interesting and in my opinion the last gasp the von Neumann
architecture will go through is going to be a combination of graphene and
photonics. Of course not in the next 10 years, but let's hope for the next 30.

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daviddumon
It may be hard to correctly anticipate what impact this breakthrough will
have, but i get the sense that this combine with quantum computing could
change our future pretty quickly. I feel excited about it and frightened at
the same time ...

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jaibot
Looks like they're pretty unrelated accomplishments; this enables faster
interchip communication, while quantum computers enable speedup of a very
specific subset of problems if you can get enough qubits within a chip to play
nice.

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Strilanc
Communicating between quantum computers will probably involve photons. They're
pretty good at traveling far fast coherently.

... Not good enough that we won't need to use a quantum error correcting code
and repeaters that pump out the decoherence errors along the way, but still
important.

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hackeram
Could anyone throw some insight on how this would help sensors in future
(apart from low power consumption)?

Reference from the article - "Further down the road, this research could be
used in applications such as LIDAR, the light radar technology used to guide
self-driving vehicles and the eyes of a robot; brain ultrasound imaging; and
new environmental biosensors. "

