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♤ Holographic versatile disc (HVD) is a holographic storage format that looks like a DVD but is capable of storing far more data. Prototype HVD devices have been created with a capacity of 3.9 terabytes (TB) and a transfer rate of 1 gigabit per second (1 Gbps ). At that capacity, an HVD could store as much information as 830 DVDs or 160 Blu-Ray discs.
♤ To increase capacity, holographic storage uses laser beams to store digital data in three dimensions, rather than in two dimensions as in CD and DVD media. HVD is, essentially, a holographic layer built on top of a conventional disc. The HVD process uses a blue-green laser beam, used for reading and writing data, collimated (made parallel) with a red laser beam, which is used for servo and tracking.
♤ In the recording process, the initial laser is split into two beams. One of the beams passes through a device called a spatial light modulator (SLM) and combines with the direct beam to produce a hologram in the physical medium. To recover the data, another 532-nm laser is directed into the hologram, which diffracts the laser beam. The resulting image constitutes an optical reproduction of the original recorded data. A photosensitive semiconductor device converts this optical data into the original digital files.