Optical, opto-electronic, photonic functional components Digital disc storage enters the third dimension
European researchers have created a prototype holographic technology that could ultimately store one terabyte, or 1,000 GB, of data on a disc the size of a DVD.
With the Microholas holographic data-disc storage system, a good chunk of the internet could be stored on a few hundred discs. The advance would provide a very simple and comparatively cheap archiving system for digital libraries, server farms and public and private databases. The system works by layering data and varying the laser wavelength or recording conditions to create a three-dimensional 'stack' of data in a tiny space.
50 data layers
Currently, standard data-disc technology uses surface structures only, but the system created by the EU's Microholas project works by using nanostructures throughout the depth of the disc. The system creates a disc that stores data in three dimensions. The project's researchers entered the third dimension by applying two lasers to the disc. Refractive and interference patterns created by the two lasers create a three-dimensional holographic grid matrix.
This grid matrix is composed of a series of layers, and the prototype has 50 data layers in its grid.
Then the researchers used wavelength multiplexing - simply lasers of different frequency - to access the different layers. Using this technique, the team successfully created a DVD-sized disc demonstrating a capacity of 150GB. The ensemble is called a microholographic disc (MHD).
Terabyte in 2010
The team developed a complete system composed of recorder, reader and disc, and they now hope to perfect the technology to create a terabyte model by 2010. By comparison, a double-layer bluray disc, the largest DVD-sized storage medium currently available, can hold just 50GB of data.
The promise of a new data technology capable of storing 1 terabyte of data on a DVD disc represents a staggering advance in the field. To put the advance in perspective you need to compare the storage capacity with something really, really big, like the internet, for example.
In 2003, the surface internet - fixed web pages - was 167 terabytes, according to the Information Management & Systems department at the University of California, Berkeley. So just 200 MHD discs could store the entire surface web. The technology is not intended for media distribution, like movies and software. The researchers will focus on developing it for digital archiving and long-term storage.
As such, the Microholas project is very much of the moment. Increasingly, the world's cultural heritage is stored digitally, but current digital media technology is not as durable as its analogue counterparts, such as books.
Books can last hundreds of years, but digital optical storage like DVDs have an upper theoretical limit of 50 years, according to a British Library report.
It may seem counter-intuitive. Plastic lasts a long time. But digital information on a DVD is very delicate. If there is any degradation in disc integrity, the data becomes unreadable, and 50 years is the upper limit.
A robust data-preservation strategy must replace aging digital disks regularly, and that gets expensive unless you have a low-cost, high-density storage system. It is a serious problem.
Digital Dark Age
Researchers at the Microholas project warn that society could face a digital 'Dark Age', with vast tracts of cultural heritage lost, if a robust preservation and storage strategy is not developed.
Much of the world's analogue culture patrimony, such as books, exists in both digital and analogue media. But much, much more only exists digitally.
MHD offers the low-cost, high-density storage answer to the digital preservation question. The project team believes the microholographic discs could be manufactured cheaply and hopes to attract the interest of manufacturers.
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Funding SchemeSTREP - Specific Targeted Research Project
H 1116 Budapest