Holographic Versatile Disc

The Holographic Versatile Disc (HVD) was a proposed optical disc technology designed to store up to several terabytes of data on a 10 cm or 12 cm diameter disc. Development began in April 2004, but the project was ultimately abandoned due to funding issues. One of the companies responsible for its development went bankrupt in 2010.

The smaller disc size was aimed to reduce costs and materials used. It employs a technique known as collinear holography, whereby a blue-green and red laser beam are collimated in a single beam. The blue-green laser read data encoded as laser interference fringes from a holographic layer near the top of the disc. A red laser is used as the reference beam to read servo information from a regular CD-style aluminium layer near the bottom. Servo information is used to monitor the position of the read head over the disc, similar to the head, track, and sector information on a conventional hard disk drive. On a CD or DVD this servo information is interspersed among the data. A dichroic mirror layer between the holographic data and the servo data reflects the blue-green laser while letting the red laser pass through. This prevents interference from refraction of the blue-green laser off the servo data pits and is an advance over past holographic storage media, which either experienced too much interference, or lacked the servo data entirely, making them incompatible with current CD and DVD drive technology.