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Sharp doubles optical storage density

12 Jul 2005

Sharp invents a super-resolution optical disc that can hold 100GB of data.

Sharp has developed a blue-laser storage technology that is capable of holding twice as much data per layer (50GB versus 25GB) than the Blu-Ray disc format which is now entering the market.

The Japanese electronics firm will unveil a 100GB dual-layer “super-resolution” optical disc at a conference on optical storage and memory (ISOM/ODS 2005) which is taking place in Hawaii this week.

Sharp claims that its super-resolution format holds up to 9 hrs of high-definition television (HDTV) footage in a dual-layer optical ROM disc. Each layer consists of a series of tiny data marks (pits and bumps) covered by thin transparent “super-resolution” film.

The film’s thermo-optic properties enable a very high resolution data read-out that actually beats the optical diffraction limit. This means that it is possible to identify data marks that are smaller than the footprint of the laser beam, leading the way to higher density storage.

Sharp’s scheme uses a blue laser beam with a diameter of around 400 nm to read data marks that are just 100 nm wide. Although the laser beam illuminates several marks simultaneously, heating-induced differences in the film’s optical transmission allow a distinction between the pits and bumps.

According to Sharp, it has been searching for some time for suitable materials to create a film with the high optical transmission that is needed for a multiple layer disc. It says that it has now found a metal oxide that is up to the task.

Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.

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