holographic versatile disc (HVD)
The HVD disc(HVD) is a mass storage device that uses holographic storage. Like optical storage discs, it has a diameter of 12 cm. Constructed as a multi- layer disc, the storage capacity of an HVD disc, which can be up to 3.9 terabytes( TB), exceeds that of a DVD by a factor of 850 and even that of an HD DVD by a factor of almost one hundred. The data transfer rate of the HVD disc is said to be 1 Gbit/s.
The HVD disc works with two lasers whose two beams are combined into one beam: a green- blue laser and a red laser. The green-blue laser beam reads the data from the holographic layer, which is stored there as coded interference patterns.
The modulated laser beam is reflected by the underlying layer, which performs the function of a dichroic filter. The red laser beam, on the other hand, reads the auxiliary and control information stored on an aluminum layer as pits and lands. For this purpose, the red laser beam passes through the holographic and dichroic layers and is reflected from the pits and lands on the aluminum layer. This control information is needed to control the read head and is comparable to the sector, head and segment information of conventional hard disks.
The development of the HVD was already started in 2004, but there are no marketable products to date (2020).