Holographic memory is a crystal or photopolymer-based, next-generation memory storage technology competing with many others for dominance of the future computer memory market. It is currently in the research and development stage, meaning that many successful prototypes have been built, but the technology is still being improved and has not yet been commercialized. Commercialization is expected in late 2006, when both Optware and Maxwell will release variants of the Holographic Versatile Disc capable of containing 200 gigabytes (GB) and 300GB of data, respectively. In a few years, the mature form of the disc is expected to reach the market. This model will hold almost 4 terabytes (TB), or 4000GB, enough to contain 8,700 hours of video.
Like other forms of optical data storage, holographic memory uses lasers to encode data in the medium. However, instead of using a series of pits and grooves to store data, as in a compact disc, holographic memory is encoded as an interference pattern between two lasers. These two lasers are referred to as a the reference beam and the signal beam. The signal beam holds the data, while the reference beam usually stays constant. Because writing to the disc creates a hologram, a complex 3D pattern in the crystal, all it takes is shining a reference beam at the disc at a precise angle for the original image to be projected again.
Holographic memory technology circumvents the limitations on conventional optical memory storage technologies by making use of inherently three-dimensional holography to encode data, rather than conventional 2D read-and-write-by-laser-beam. This means that the entire volume of the crystal can theoretically be used to encode holographic memory data, though in practice this is not possible. Still, any degree of three-dimensionality is a great advantage for an optical memory storage technology, enough to put holographic memory leaps and bounds ahead of DVD and Blu-Ray technology.
Multiple holograms can be layered on top of one another in the same medium, a quality known as multiplexing. By changing the angle of the reference beam, an entirely new image can be encoded and subsequently projected. Each tiny change to the angle of the crystal can give rise to an entirely new reconstituted holographic image, almost up to the limit of the atoms of the crystal itself to hold information. Holographic memory is a technology that is different-in-kind from what came before it.