Holographic storage company InPhase Technologies announced this week that it has broken a storage density record by writing 64.3 gigabytes of data onto a single square inch of disc space. This advance could eventually lead to a holographic disc that can hold more than 100 DVD-quality movies, according to the company. By comparison, magnetic disks, such as those in the hard drives of computers, can manage a storage density of about 37.5 gigabytes per square inch of disk.
“We’ve now demonstrated that we’re more than two years ahead of magnetic storage,” says Kevin Curtis, chief technology officer of InPhase, a Longmont, CO, company. Curtis explains that while magnetic storage – the leading option for storing large amounts of data – is quickly approaching its physical limit, holographic storage will grow rapidly without major technological overhauls for at least another five to six years.
InPhase plans to release its first two products at the end of this year: a holographic disk drive and a 300-gigabyte disc. This rollout will be followed by 800-gigabyte discs in 2008 and 1.6 terabyte (1,600 gigabyte) discs in 2010, which, Curtis says, will be compatible with the holographic disk drive released in 2006.
The concept of using a hologram – a three-dimensional image generated by lasers – to store information dates back to the 1960s (see Holographic Memory). But it’s only been within the last five years that the optical storage technology has become feasible, says Demetri Psaltis, electrical engineering professor at the California Institute of Technology. One reason the technology is now more commercially viable is because the lasers needed to read and write data have become smaller and cheaper.
Other types of optical storage disks – CDs, DVDs, Blu-Ray, HD DVD – also use lasers to read and write information. However, they can keep data only on their surfaces, whereas holographic products store data in three dimensions – the key to holding an entire movie library on a single disc.
To write three-dimensional information to a disc, engineers exploit the fact that beams of light, when crossed in a certain way, generate holograms. The process begins as a single blue laser beam is split into the signal beam and reference beam. Information is encoded into the signal beam as a pattern of light and dark pixels, representing 0s and 1s. When the signal beam is crossed with the reference beam, a three-dimensional hologram of the array of pixels is imprinted into a photosensitive medium in the disc.
This array is called a “page” of data; InPhase’s discs contain about 1.3 million bits of data per page, says Curtis. Furthermore, he explains, multiple pages can be placed at slightly different angles to each other, to make up what he calls a “book.” Angling the pages allows the engineers to place numerous pages within the same three-dimensional disc space, maximizing the amount of data that can be stored within a disc.
The record storage density was achieved by creating 320 data pages per book. Each page was offset from the next one by an angle of just 0.067 degrees. Three tracks were then created, spaced 700 micrometers apart. In order to further increase capacity, Curtis says, the company will increase the number of pages per book by reducing the angle between pages even more, and also by reducing the spacing between the books to 480 micrometers.
Their achievement is “a major milestone” for holographic data, says Han Coufal, manager of science and technology at IBM’s Almaden Research Center in San Jose, CA. “It shows upward mobility and a roadmap to higher and higher density.”
The most immediate commercial application for this higher-density storage, Curtis says, is in archival data storage. There, storage demand is increasing, he says, as broadcasting companies create more digital content and video increasingly comes in high-definition formats, resulting in huge file sizes.
Currently, large data archives, such as those at banks, are stored on computer tape –- plastic strips with a magnetic coating – that can hold anywhere from a few kilobytes to hundreds of gigabytes of data. But this medium is easily susceptible to damage from moisture and temperature fluctuations. In order to ensure reliable recovery, “typically, people would have to rewrite to a new tape every couple of years,” Curtis notes. Holographic discs are made of plastic that is more robust than tape, he explains. InPhase has shown in harsh environmental tests that the medium is good for up to 50 years.
Hitachi Maxell, a leading producer of computer tapes and CD-ROMs, began investing in InPhase in 2002. But while InPhase has a solid business partner, the technology is still relatively young and hasn’t proven itself in the marketplace. Indeed, a drive will cost as much as $1,500, and each disc, which is 10 centimeters across and 1.5 millimeters thick, will be priced at $120 – many times the cost of computer tape drives and disks. Additionally, holographic discs are not currently rewritable. Curtis says that InPhase is working on rewritable technology, but it most likely won’t be available for a couple years.
As holographic technology continues to develop rapidly, though, Curtis says there is no reason why future holographic discs can’t be smaller, and built into consumer electronics such as cell phones, PDAs, and MP3 players. A disc the size of a postage stamp could hold 25 gigabytes of data, he says, or the equivalent of 6,250 songs. InPhase is still in the early development stages of holographic storage for consumer devices, however. “It’s still a few years out,” Curtis says.
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