Boffins build basis for 9TB DVDs

All down to the longitudinal surface plasmon resonance of gold nanorods, don't you know

Optical Disc

Aussie scientists have devised a digital disc design capable of holding the content from 2000 DVDs - more than nine terabytes of data - in a unit physically no bigger than a DVD or Blu-ray Disc.

In a paper entitled Five-dimensional optical recording mediated by surface plasmons in gold nanorods and published today in the journal Nature, researchers Peter Zijlstra, Dr James Chon and Professor Min Gu of the Swinburne University of Technology's Centre for Micro-Photonics in Melbourne, Australia describe a "multiplexed optical recording" system that's capable, they calculate, of an "information density beyond 10^12 bits per cm³".

The proposed disc structure uses a two-dimensional array of the gold nanorods. Multiple layers extend this basic structure into three dimensions, the team demonstrated.

The extra two "dimensions" described in the paper are the wavelength of light - its colour, essentially - and polarisation, allowing every one of the data storage points to hold encode even more information.

The nanorods' colour is governed by their shape, set by heating the nanorod up until it melts and, with the right incident laser light, re-solidifies on cooling.

The gold nanorods also polarise the light, and by adjusting the degree of polarisation, the scientists were able to encode information that way too.

Reading back the information involves heating each nanorod and examining the colour and polarisation of the light it emits. Heating the nanorods to read the information doesn't destroy that data.

The researchers admitted that all three techniques - spatial, wavelength and polarisation - have been proposed before, but separately. They contend they're the first to find a material that can by used to apply all three techniques.

The best bit: all this extra data comes at no cost to the disc's size, said Gu.

Plenty more work needs to be done, he admitted, most importantly the speed at which data can be stored on a disc. The team's data-recording surface isn't a disc and it doesn't rotate. It also requires a large and complex apparatus to read the information back - all a long way from a thin 12cm disc you can slot in a PC peripheral.

However, Gu reckons discs based on his team's design could become a commercial reality within five to ten years. ®

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