To prove their point  the first DVD–sized discs with storage capacities well over one terabyte could be available in as little as five years through a concept, which the researchers have already demonstrated on test media, using layers of gold nanorods to achieve 'five–dimensional recording'. (Right 7D)

CDs and DVDs, store data as a spiral track of microscopic pits etched onto their surface. Light from a laser diode is reflected from the surface and the reflected light drops in intensity every time the laser reading beam hits a pit. At one layer of pits storage is 2D, with multiple layers, capacities up to about 17 GB, storage is 3D.

To reach above 1TB (1012 bytes), scientists believe they will need to be able to record in more 'dimensions' and achieved success in adding one extra dimension in the form of sensitivity to either the polarization or colour of the laser light, a technique called multiplexing.

Now, James Chon and colleagues from Swinburne University of Technology in Melbourne   combined both types of multiplexing for 5D recording.

"Previously there has never been an effort to record in all five dimensions," Chon told  Physics World  "This is due to a lack of material that can respond in all five-dimensional recording conditions — colour, polarization and spatial."

For its recording media, the researchers used gold nanorods, responding to different colours and polarizations depending on apparent size and orientation. When nanorods are irradiated with laser light, only those that are aligned to the light's polarization and have an absorption cross-section matching the light's wavelength will absorb it, melt and change in shape. Because there are nanorods left unaffected after one recording, more recording cycles can still take place.

To read the data a laser again illuminates the nanoparticles, which begin to resonate with quasi-particles known as plasmons. The plasmon resonance is very sensitive to the incident light's polarization and colour, and requires a laser that is only a hundredth as powerful, so no more melting takes place.

Compatible with existing technology In tests using media with three layers of gold nanorods, Chon and colleagues achieved a data storage density of 1.1 Tbit per cubic centimetre, which would equate to 1.6 Tb for a DVD–sized disc. Researchers think that by using thinner spacers between layers, capacity could be increased to 7.2 Tb and say  recording speeds could be as fast as 1Gb/s, with discs compatible to existing technology.

Chon says the group is collaborating with Samsung to commercialize the concept, and hopes to see the first devices on sale in five years. "We have only conducted proof-of-principle experiments," he adds. "It is our future work for this technology to be transferred to industry, where many challenges will have to be overcome."

Still why stop at five if we can get to seven or nine?