Holographic Versatile Disc

Holographic Versatile Disc (HVD) is an optical disc technology still in the research stage which would greatly increase storage over Blu-ray and HD DVD optical disc systems. It employs a technique known as collinear holography, whereby two lasers, one red and one blue-green, are collimated in a single beam. The blue-green laser reads data encoded as laser interference fringes from a holographic layer near the top of the disc while the red laser is used as the reference beam and to read servo information from a regular CD-style aluminium layer near the bottom.