The Holographic Versatile Disc (HVD) is an optical disc technology. It can hold many times the amount of information of a Blu-ray disc. It employs a technique known as collinear holography, whereby two green laser beams 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 servoinformation from a regular CD-style aluminum layer near the bottom. Servoinformation 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 reflects the green laser while letting the red laser pass through. This prevents interference from refraction 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. These discs have the capacity to hold up to 6 terabytes (TB) of information. The HVD also has a transfer rate of 1 Gbit/s (125 MB/s). Sony, Philips, TDK, Panasonic and Optware all plan to release 1 TB capacity discs in 2019 while Maxell plans one for early 2020 with a capacity of 500 GB and transfer rate of 20 MB/s—although HVD standards were approved and published on June 28, 2007, no company has released an HVD as of May of 2010.
Current optical storage saves one bit per pulse, and the HVD alliance hopes to improve this efficiency with capabilities of around 60,000 bits per pulse in an inverted, truncated cone shape that has a 200 micron diameter at the bottom and a 500 micron diameter at the top. High densities are possible by moving these closer on the tracks: 100 GB at 18 microns separation, 200 GB at 13 micrometers, 500 GB at 8 micrometers and a demonstrated maximum of 5 TB for 3 microns separation on a 10 cm disc.
The system uses a green laser, with an output power of 1 watt which is quite high power for a consumer device laser. So a major challenge of the project for widespread consumer markets is to either improve the sensitivity of the polymer used, or develop and commoditize a laser capable of higher power output and suitable for a consumer unit.
HVD is not the only technology in high-capacity, optical storage media. InPhase Technologies was developing a rival holographic format called Tapestry Media, which they claim will eventually store 1.6 TB with a data transfer rate of 120 MB/s, and several companies are developing TB-level discs based on 3D optical data storage technology. Such large optical storage capacities compete favorably with the Blu-ray Disc format. However, holographic drives are projected to initially cost around US$15,000, and a single disc around US$120–180, although prices are expected to fall steadily. The market for this format is not initially the common consumer, but enterprises with very large storage needs.