Holographic storage systems use light beams to store information in a block of physical material. This technology has been under development for some 40 years, and the first patents appeared in the late 1960s. But the high cost of component parts and the lack of a suitable storage material have prevented the creation of marketable products.
However, recently the cost of components such as lasers and lenses has fallen, and their performance has improved. As a result, the need to find a suitable optical medium has become the main stumbling block. Such a material needs to be very light-sensitive and also needs to reliably store data under varying temperatures, pressure and humidity.
Research teams have been working on this, but they are often reluctant to talk about their progress. Teams from IBM and Kodak, as well as universities, and specialist startups such as Cambridge University offshoot Polight Technologies, are among those working on the problem.
Photo-polymer
Now, InPhase Technologies, a recent spin-off from Lucent Technologies, says it has a new photo-polymer that exhibits all the qualities needed for a commercial holographic storage medium. With this polymer, InPhase believes it has all the components to bring affordable holographic data storage to market. Bill Wilson, chief scientist at InPhase, said 400GB of usable data  in addition to error correction and other data  has been stored in a square inch of the polymer in a laboratory prototype. Wilson estimated that a storage device could be manufactured for less than £1,000 for 150GB. This technology could be very attractive to corporates, not least because data transfer rates of up to one billion bits per second are possible using lasers. However, the capabilities of InPhase's early devices will be more modest.
Wilson said the first products will use a moving laser device, because non-mechanical steering of laser beams is relatively expensive at present. He estimated transfer rates will be between 30MB/s and 50MB/s, with data accessed in increments  sometimes referred to as pages of data  of 1.3MB or less. These figures compare with typical magnetic disk transfer rates of 300kB/s and 4kB per page. With these characteristics, holographic storage may meet corporate demand for huge data capacities coupled with fast retrieval.
However, Michael Ledzion, chief executive of Polight Technologies, was sceptical of InPhase's announcement that it had found a suitable polymer.
'The downside of writing to a polymer is that the whole thing moves,' he said, and explained that if this happens the data may become distorted. Ledzion said his company was currently working on a non-polymer material and would make an announcement later in the year.
Simon Shepherd of analyst firm IDC said, 'There has recently been a resurgence of interest in holographic storage. I would be a little cautious of estimates of two to three years [for product availability].' But he added that parallel technological developments meant that computers should be able to handle faster data transfer if it becomes available commercially.
Wilson said InPhase's new class of photo-polymers use a two-chemical process involving two linked molecules that are changed by light  most polymers previously created for holographic storage work on only one molecule. 'A prototype test device should be available in about a year,' he said.
Single coherent laser
Another difference between InPhase's system and earlier systems is that InPhase uses a single coherent laser instead of two lasers with intersecting beams. The single beam is split in two using a modulator, producing a signal data-carrying beam and a reference beam. These overlap within the photosensitive storage medium producing an interference pattern. During read-out an identical reference beam is used to diffract away the pattern to leave the pure data. Writing at different depths in the holographic storage material is achieved by altering the angle of incidence or the wavelength.
Wilson said there are several reasons why holographic storage is now a commercial likelihood. 'This is the first time you can buy enough parts to build a prototype. You can now get a relatively low-cost laser, modulators and a fast enough camera,' he said.
Commenting on the cost of holographic storage, IDC's Shepherd said, 'It will be interesting to see what the price is. There's likely to be a huge premium initially.'
Wilson said corporates would probably be the first customers for holographic systems. 'As of now, a holographic device is probably overkill for the consumer. The first applications may be video-type functions where very large objects are needed,' he said. He hinted that a high-performance high-capacity DVD, possibly in write-once-read-many (Worm) format initially, could be developed.
After 40 years of development, widespread use of holographic storage may finally be approaching.
