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Boffins light way to photonic computing with 1PB DVD tech

Smallest-ever laser dot shines a light on silicon alternatives

Successive generations of optical media generally rely on a new laser and a medium capable of responding to the new laser's qualities.

And so it is with a new piece of research, titled Three-dimensional deep sub-diffraction optical beam lithography with 9nm feature size [PDF], revealed today that it may one day be possible to achieve areal density of a petabyte (1000TB) on a single 12cm platter.

There's a bit more to this “breakthrough” than just another “oh look future storage could be much bigger” revelation.

As the authors from Swinburne University's Centre for Micro-Photonics explain, the lasers involved get around a property of light called “Abbe's Limit”. The authors of the paper have published a lay-person's explanation of it here that says “the diameter of a spot of light, obtained by focusing a light beam through a lens, cannot be smaller than half its wavelength – around 500 nanometres (500 billionths of a metre) for visible light.”

The head of a pin is one million nanometres across, so 500nm is still lovely and small. But if one can get the spots of light lasers make even smaller, and shine those dots on an optical medium, we get the chance for more information to be packed onto a disk.

Here's how the researchers explain their technique for making even smaller lasers:

In our study, we showed how to break this fundamental limit by using a two-light-beam method, with different colours, for recording onto discs instead of the conventional single-light-beam method.

Both beams must abide by Abbe’s law, so they cannot produce smaller dots individually. But we gave the two beams different functions:

  • The first beam (red, in the figure right) has a round shape, and is used to activate the recording. We called it the writing beam
  • The second beam – the purple donut-shape – plays an anti-recording function, inhibiting the function of the writing beam
  • The two beams were then overlapped. As the second beam cancelled out the first in its donut ring, the recording process was tightly confined to the centre of the writing beam.

This new technique produces an effective focal spot of nine nanometres – or one ten thousandth the diameter of a human hair.

The team has also developed a new “photoresin” that is sensitive to the differences between the two beams and their overlaps so it can produce readable markings that represent data. Professor Min Gu, lead author of the paper, told The Reg his labs have working disks featuring the new photoresin and are working on drives.

But Professor Gu also said the lab is considering applications beyond storage, especially optical/photonic computing.

To understand why that's worth considering remember that Intel proudly talks up its 22nm manufacturing process and innovations to extend its life, but has to contend with the fact that electrons won't get smaller any time soon which makes it hard to build chips on smaller scales.

Plenty of energy (pardon the pun) is being expended on photonic/optical computing as a way around that problem, as photons' slippery qualities mean even 22 =nm leaves plenty of wriggle room. And that's where Professor Gu thinks 9nm lasers may shine (pardon the pun again).

Of course there's a long way to go before anyone slaps a “9nm Inside” sticker on an a Mark 12 IntelPad or hands you a 1PB disk. But hey: science just reduced lasers from 500nm to 9: let's enjoy that achievement before we lust after its appearance in our pockets. ®

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