As the war rages over what format will make up the next generation of DVDs, signs of an impending battle over their successors are already in the air.
A new type of disc that promises to cram in up to 300 times as much data as today’s DVDs is poised to hit the market, and a similar, rival disc whose data is recorded and read differently is to be released within a few years.
The new discs use a holographic technique to store data in three dimensions. At first they will be used by businesses and governments to back up their vast archives, but in a few years they could hit the consumer market, with one disc able to store multiple high-definition movies. “We expect holographic storage to be really huge,” says Mukul Krishna, an analyst with Frost and Sullivan based in San Antonio, Texas, who specialises in digital media.
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“We expect holographic storage to be huge. It could hit the consumer market in a few years”
Because two different ways of recording to and reading the discs are emerging, the new standard could result in a second DVD war, like the one now taking place between rival high-definition formats HD DVD and Blu-ray. “Whenever you have an emerging technology there is always a danger of this happening,” says Krishna.
Holographic storage was first proposed over 40 years ago by Pieter van Heerden of Polaroid Research Labs in Cambridge, Massachusetts, but a suitable material for the discs proved elusive. Now two companies have come up with discs made of light-sensitive polymers that they say are up to the job. InPhase Technologies in Longmont, Colorado, is expected to release its disc within the next few months, while a product from DCE Aprilis in Maynard, Massachusetts, will be a few years in the making.
At first InPhase’s discs will be capable of storing 300 gigabytes of data – that’s 12 times as much as a single-sided Blu-ray disc and 60 times the capacity of a standard DVD. Within a few years this is expected to ramp up to a colossal 1.6 terabytes – around 300 times more than an ordinary DVD. DCE Aprilis is aiming for similar capacity with its discs.
Such high storage density is possible because, unlike conventional DVDs, which use reflective bumps on their surface to store data, holographic discs embed data throughout their thickness. Like holograms, in which multiple images are stored at the same point to create the illusion of a 3D object, holographic storage records “pages” of 1s and 0s in the same space. The result is that hundreds of pages can be stored in one microscopic area.
Although the two types of disc use different light-sensitive polymers, they rely on the same principles of holographic storage (see Diagram). Digital data to be stored is converted into a series of black and white pixels on a transparent LCD “page” inside the disc drive. Each pixel represents either a 1 or a 0 and each page holds around 1 million pixels. A laser beam is passed through the page, creating a “signal” beam with a pattern of light and dark patches that corresponds to the page. A set of mirrors inside the drive then directs a second “reference” beam to the disc’s surface, where it combines with the signal beam to create an interference pattern with a new arrangement of light and dark patches. The disc’s photosensitive polymer then stores the pattern. It does this by joining up small monomer molecules interspersed within it to form longer chains in the regions hit by light patches, while the monomers remain disconnected in the dark regions.
Crucially, the angle at which the light from the interference pattern hits the polymer ensures that only some of the monomers at that point react to the light. This enables hundreds of pages to be written at the same point on the DVD’s surface: each one is stored by shining the interference pattern onto the polymer at a slightly different angle.
A page is read by shining a reference beam onto the point at the exact angle that was used when the data was encoded. The beam that diffracts off the material will contain a pattern of light and dark patches that exactly reproduces the original signal beam. This is then translated back into a series of 1s and 0s.
Here, though, is where the similarities between the InPhase and DCE Aprilis technologies end. DCE Aprilis’s discs can read and record discs very fast, in excess of a gigabyte per second, according to David Waldman, the company’s chief scientist. In contrast, InPhase’s drives currently read at a maximum speed of 20 megabytes per second and record even more slowly.
This is because the compounds used by the two companies react to light in different ways. InPhase’s polymer undergoes a process called “free-radical polymerisation”, whereas the Aprilis polymer uses “cationic ring-opening polymerisation”. Free-radical polymerisation requires light of a higher intensity than the ring-opening version, so the interference pattern must be shone on InPhase’s polymer for longer to result in a recording, slowing the process down.
What InPhase lacks in speed it makes up for in having a market-ready product. Its Tapestry 300R drives are already being shipped to several electronics companies, with a wide-scale launch scheduled for the second half of the year, says Liz Murphy of InPhase.
At 13 centimetres across the discs are slightly larger than a conventional DVD, and are encased in a protective cartridge. The drives have a 15-centimetre-square front and are 60 centimetres deep.
Costing $18,000 for the drive and another $180 for each disc cartridge, the InPhase equipment is unlikely to appeal to even the most memory-hungry home user. Instead, InPhase’s first customers will be organisations that generate hundreds of gigabytes of data each day, such as government agencies, broadcasters, medical organisations and IT companies. “If you’re generating that much data it can become unmanageable,” says Murphy (See “Where to put all that data”).
The polymer developed by DCE Aprilis is more likely to find its way directly to consumers. The company’s partners, which include Sony, are aiming to eventually produce a mass-market replacement for Blu-ray and HD DVD. “Every single large consumer electronics company in Japan and South Korea is testing and evaluating our materials,” says Waldman. InPhase says it plans to roll out consumer applications for holographic memory at a later stage.
Having such huge storage capabilities for entertainment may seem like overkill – after all, do we really need to be able to store multiple high-definition movies on a single DVD? But as image resolutions become ever higher, even Blu-ray and HD DVD are likely to feel the strain.
If both companies do move into the high-definition movie market as planned, it could create a headache for consumers. Like the Blu-ray and HD DVD formats, which both store high-definition video but are read using different hardware, a rivalry could emerge between the DCE Aprilis and InPhase technologies.
InPhase records and reads discs by shining a series of lasers at the same point at hundreds of different angles then moving on to the next point. This means the disc does not spin, but instead constantly stops and starts. Because the DCE Aprilis disc can be read faster, it spins continuously. This difference in approach will require different readers, potentially forcing consumers once again to choose between one standard and another.
One problem that remains is that holographic discs are not yet rewritable. Both companies are working on a solution, but given the vast gulf between the way the two systems record it seems likely that there will be an even greater difference between the way they can be rewritten.
Where to put all that data
While holographic storage might one day replace Blu-ray or HD DVD as the medium for high-definition video recordings, its first application will be backing up the hundreds of gigabytes of data generated by government agencies, broadcasters, medical firms and IT companies every day.
At the moment the only method that is fast and cheap enough to back up this quantity of data is good old-fashioned magnetic tape, says Immo Gathman of the German jukebox manufacturer DSM. But even modern tape formats typically only last about 10 years and have to be played periodically to avoid degradation. To take advantage of holographic storage technology, DSM has signed a deal with InPhase Technologies of Longmont, Colorado.
Ironically, another problem with existing methods for mass digital storage is that, like their paper counterparts, how much you can store often comes down to how many square metres of space you have. Just last month Google and NASA announced a deal that involves the internet giant taking over part of the role of managing the huge volumes of data the space agency recovers. It has been reported that Google will be given nearly 100,000 square metres of warehouse storage space. All this points to a dire need to develop much denser digital storage mediums, says Liz Murphy of InPhase.
