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*Optical technique promises terabyte disks*

17:07 27 September 04


A novel method of optical data storage could soon be used to hold a 
terabyte of data on a disk the size of a normal DVD, say researchers at 
Imperial College London, UK.

Information is encoded on a normal DVD in the form of microscopic 
indents on the surface of the disk. The presence or absence of an indent 
corresponds to a binary piece of information - a ‘1’ or a ‘0’. Indents 
are detected by beaming light onto a disk with a laser and measuring the 
amount of light that bounces back.

Using tracks embedded at several depths within a disk, it is possible to 
store more data on the highest capacity disks. Multilayer DVDs hold 
about 16 gigabytes of data, which equals about 8 hours of high quality 
video.

But the researchers realised that the polarity of light might also be 
used to encode information. They developed a type of disk that 
incorporates angled ridges within the pits in order to subtly alter the 
polarity of the light that gets reflected. This can be used to store 10 
times’ more data than is currently possible, they say.


*All-in-one disk*

Using the technique, the researchers think it should be possible to 
create disks capable of holding 250 gigabytes in a single layer. This is 
enough to store 118 hours of video, which could allow every episode of 
long-running television shows to be put on one disk. Using a four-layer 
disk would mean a terabyte could be stored.

In the new system, light polarised in a single direction is beamed onto 
the surface of the disk. Some bounces back with a polarity at 90 degrees 
to that of the original beam. By measuring how much light comes back in 
each of the two directions, it is possible to work out the precise angle 
of the slope.

"We’re using an added property of light not utilised by conventional 
methods," researcher Peter Munro told *New Scientist*.

The most advanced optical storage disks available today use a technology 
known as Blu-ray and can hold roughly 100 gigabytes of data. Blu-ray 
makes use of blue light instead of red, which has a smaller wavelength 
and can therefore read smaller areas of a disk's surface.


*Mini-disks*

The researchers say information could be encoded using 10 different 
angles of slope, corresponding to 10 bits of information in each indent. 
Provided funding can be found, the team believes it should take about 
five years to perfect the technology and a commercial version could be 
available by 2010.

Wolfgang Schlichting, research director of the removable storage 
division of US analyst firm IDC, says there should be plenty of demand 
for disks that can hold so much information. He suggests that miniature 
disks based on the technology would also be popular.

But Schlichting also warns that the new method could prove costly to 
develop. "Typically, optical storage technology based on the polarity of 
light are more difficult to implement and so more expensive," he told 
*New Scientist*.

Munro also says they have not yet determined out how a consumer writing 
device could be made. But he believes this could be seen as a bonus. 
"Creating pirate disks would be very difficult unless you bought the 
mastering equipment," he says.

Will Knight

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