After years of development, researchers are on the verge of using holograms to store data in memories that are both fast and vast

The notion of holographic memory dates back to 1963, when Pieter van Heerden, a researcher at Polaroid, first proposed using the method to store data in three dimensions. In theory, it is a great idea. Existing media store data in only two dimensions. Adding a third would make storage devices far more efficient. But despite massive spending over four decades, a complete, general-purpose system that could be sold commercially has eluded both industrial and academic researchers.

It is still elusive. But it is getting closer. The first commercial holographic memory should be on the market next year, and more are expected to follow. When that happens, there may be a ballooning of computer storage capacity that will make existing disks look like leaflets compared with the Encyclopaedia Britannica.

Holographic data-storage works by recording the differences between two beams of laser light. The first is a reference beam that contains no information. The second carries data that it has picked up by being passed through a liquid-crystal panel known as a spatial light modulator.

Where the two beams intersect, they interfere with one another, and this interference pattern can be captured by the photosensitive molecules of a storage medium located in the overlap region. The result is a hologram, which can be read by applying a beam equivalent to the original reference. This produces a replica of the original data.

The real beauty of holography is that a huge number of holographic files can be stored in an overlapping manner in the same volume of photosensitive material. All that is required for this to happen is that the reference beam for each hologram must arrive at a slightly different angle from all other beams, or must have a different wavelength from those beams. Theoretical calculations suggest that it will be possible to use holographic techniques to store a terabyte (1,000 gigabytes) of data on a CD-sized disk. Today’s DVDs, by comparison, have a storage capacity of less than 20 gigabytes.

Moreover, holographic techniques permit the retrieval of data at speeds not possible with current storage methods. Transfer rates of a billion bits a second (at least 60 times faster than current DVDs) have already been demonstrated in the laboratory. Such fast access times are possible because the laser beams that are central to holographic technology can be moved rapidly, without inertia, unlike the components of a conventional disk drive. In short, no other storage technology in development can match holography’s capacity and speed.

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