15-06-2012, 03:37 PM
HOLOGRAPHIC VERSATAILE DISC
Abstract:
The Holographic Versatile Disc (HVD) is an optical disc technology developed between April 2004 and mid-2008 that can store up to several terabytes of data on an optical disc the same size as a CD, DVD or Blue-ray disc. It employs a technique known as collinear holography, whereby a green and red laser beam are collimated in a single beam. The green laser reads 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 aluminum 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 servoinformation is interspersed amongst the data. A dichroic mirror layer between the holographic data and the servo data of the 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.
Standards for 100 GB read-only holographic discs and 200 GB recordable cartridges were published by ECMA in 2007, but no holographic disc product has appeared in the market. A number of release dates were announced, all since passed.
Abstract:
The Holographic Versatile Disc (HVD) is an optical disc technology developed between April 2004 and mid-2008 that can store up to several terabytes of data on an optical disc the same size as a CD, DVD or Blue-ray disc. It employs a technique known as collinear holography, whereby a green and red laser beam are collimated in a single beam. The green laser reads 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 aluminum 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 servoinformation is interspersed amongst the data. A dichroic mirror layer between the holographic data and the servo data of the 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.
Standards for 100 GB read-only holographic discs and 200 GB recordable cartridges were published by ECMA in 2007, but no holographic disc product has appeared in the market. A number of release dates were announced, all since passed.