

Laser puts record data rate through fibre: 26 terabits per second - sushumna
http://www.bbc.co.uk/news/science-environment-13469924

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juiceandjuice
"The Fourier transform is a well-known mathematical trick that can in essence
extract the different colours from an input beam, based solely on the times
that the different parts of the beam arrive.

The team does this optically - rather than mathematically, which at these data
rates would be impossible - by splitting the incoming beam into different
paths that arrive at different times, recombining them on a detector."

This is cool, and makes sense.

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etherael
This sounds a bit like buffering, what impact would something like that have
on latency I wonder.

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nitrogen
At the speed of light, the latency impact of an optical implementation of the
Fourier transform operating within the confines of an equipment rack should be
negligible. In this case it sounds like they intend to implement the optical
computation directly on a silicon chip.

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joelthelion
>The trick is to use what is known as a "fast Fourier transform" to unpick
more than 300 separate colours of light in a laser beam, each encoded with its
own string of information.

No, the "trick" is decades of hard work and research in materials,
electronics, photonics, signal processing and more.

Journalists like to believe you can sum up any scientific result in one
sentence understandable by mortals. It turns out it's not the case.

~~~
mseebach
It takes a very unfavourable reading to come to that conclusion, IMO.

The particular discovery that is the core of this, is to do this transform.
That doesn't imply that (a) doing that is simple (b) getting to the point
where you can do the trick doesn't build on decades worth of science.

And, just out of curiosity, what's the alternative to simplification? "It's
fast. There's no way you'd be able to grasp why. kthxbye."

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oasisbob
Vint Cerf has stated that the theoretical capacity of fiber is 38THz of analog
bandwidth: <http://www.nnsquad.org/archives/nnsquad/msg01402.html>

I'd be interested to hear how close this record gets to the theoretical
maximum, and where the intrinsic limit comes from.

~~~
workerthread
The intrinsic limit comes from the frequency range for which the fiber is
transparent (or rather, the attenuation is low "enough"). And this in turn
depends on the composition of the glass the fiber is made from.

The wavelength range currently standardized for telecommunication is
1260nm-1675nm [1], which corresponds to 59 THz as far as I can tell. I don't
know which wavelength range Vint Cerf had in mind.

[1] [http://en.wikipedia.org/wiki/Fiber-
optic_communication#Trans...](http://en.wikipedia.org/wiki/Fiber-
optic_communication#Transmission_windows)

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patrickgzill
Can someone "compare and contrast" this with existing CWDM and DWDM
technologies, which also use different "colors" (think different frequencies,
really) traveling over the same fiber?

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oasisbob
I was wondering the same thing, and tracked down the original article:
[http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nph...](http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2011.74.html)

There's a diagram available in the abstract that compares OFDM (the technique
they use) with WDM.

Apparently OFDM only uses a single light-source, versus (C|D)WDM, which
multiplex multiple discrete wavelengths onto the same fiber.

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phlux
They are using _LASERS_ on fiber now? Sheesh - what will they think of next!
Soon you'll tell me that RADIO WAVES can be used to transmit information!

