The tantalising prospect of DVDs capable of holding almost a terabyte of data – or several hundred movies – has been presented in a patent issued to US storage company Iomega.

The US patent describes a disc that could store 40 to 100 times more information that a conventional DVD, using more nanometre-scale sloped ridges to diffract light. US patent number 6879556 – entitled “Method and Apparatus for Optical Data Storage” – was issued to Iomega on April 12 2005.

Conventional DVDs store information in the form of ridges and depressions, each several hundred nanometres wide. These correspond to bits of binary data – “1”s or “0”s. The data is read from a disc by bouncing laser light off its surface and measuring the angle at which it reflects.

The next generation of DVDs can hold almost 10 times as much data, using light with a shorter wavelength to read even smaller surface features. Two standards that use this principle are currently vying for market adoption – HD-DVD, created by Toshiba, NEC and Sanyo, and Blu-Ray Disc, from Sony.
Combining angles

However, Iomega’s proposed technology, dubbed Articulated Optical Digital Versatile Disc (AO-DVD), could boost disc capacity further still. Sub-wavelength surface bumps on an AO-DVD would slope at slightly different angles – this could be used to encode up to 100 times more information.

The angles would be detected by analysing light after it had bounced off several ridges – calculating which combination of slopes would have produced the result.

Current DVDs can hold a maximum of 8.5 gigabytes – roughly 1 billion bytes – of data, so an AO-DVD could theoretically hold more than 800 gigabytes. This is close to a terabyte and well beyond the capacity of most modern computer hard drives. Iomega claims the technique could also improve data transfer rates by a factor of 30.
Smaller wavelength

Fred Thomas, chief technologist at the company said researchers are working on “an array of mechanisms by which the state of a focused beam of light, upon reflection, can be precisely changed”. He added that smaller wavelength lasers would be crucial to developing such techniques.

Iomega is not alone in pursuing the idea for boosting DVD capacity, however. A similar technology is also being developed at Imperial College London, UK, although this uses the polarity of reflected light, instead of its diffraction, to detect sub-wavelength slope features.

Lead researcher at Imperial College London, Peter Török, claims his approach should be more efficient, but admits that success of any system will ultimately depend on the entertainment industry. “The decision as to whether to turn this into a product doesn’t depend on us,” he told New Scientist. “It depends on Hollywood.”

By Will Knight

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