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Holographic Versatile Disc (HVD) is an advanced 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. 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 amongst 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 [1]. These discs have the capacity to hold up to 3.9 terabytes (TB) of information, which is approximately 6,000 times the capacity of a CD-ROM, 830 times the capacity of a DVD, 160 times the capacity of single-layer Blu-ray Discs, and about 8 times the capacity of computer hard drives with space that accounts for year 2006 standards. The HVD also has a transfer rate of 1 gigabyte/s. Optware is expected to release a 200 GB disc in early June of 2006, and Maxell in September 2006 with a capacity of 300GB and transfer rate of 20 Mbyte/sec [2] [3].

The standards body Ecma International is leading the standard setting group for HVD, and expects to submit a proposed standard to the International Organization for Standardization for ISO approval, around December 2006. [4]

Holographic Versatile Disc structure
1. Green writing/reading laser (532 nm)
2. Red positioning/addressing laser (650 nm)
3. Hologram (data)
4. Polycarbon layer
5. Photopolymeric layer (data-containing layer)
6. Distance layers
7. Dichroic layer (reflecting green light)
8. Aluminium reflective layer (reflecting red light)
9. Transparent base



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 micrometer diameter at the bottom and a 500 micrometer diameter at the top. High densities are possible by moving these closer on the tracks: 100 GB at 18 micrometers separation, 200 GB at 13 micrometers, 500GB at 8 micrometers and a demonstrated maximum of 3.9 TB for 3 micrometer separation on a 12 cm disc.

The system uses green laser, with an output power of 1 watt, a 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.

Source: eetimes.com

Storage capacity in context

It has been estimated that the books in the U.S. Library of Congress, one of the largest libraries in the world, would contain a total of about 20 terabytes if scanned in text format. Neglecting images, the content could be stored on a little more than 6 of these discs.

At 15 meter resolution and 32-bit colour (about the resolution found in Google Earth) the land masses of Earth would occupy just over 2 TB. Using MPEG4 ASP encoding, a 3.9 TB HVD could hold between 4,600–11,900 hours of video—just over one year of uninterrupted video at usual encoding rates.<ref>Common compression rates for personal storage vary between around 780 and 2000 kbits/sec. 3.9 TB equals 2000 kbits/sec times 4,650 hours, or 780 kbits/sec times 11,930 hours.</ref>

The article notes that the transfer rate is at an average of 1 gigabit/second, or 128 megabytes/second, around 6 times the transfer rate for current 16x DVD storage. <ref>"Holographic recording technology records data on discs in the form of laser interference fringes, enabling existing discs the same size as today's DVDs to store as much as one terabyte of data (200 times the capacity of a single layer DVD), with a transfer speed of one gigabyte per second (40 times the speed of DVD). This approach is rapidly gaining attention as a high-capacity, high-speed data storage technology for the age of broadband." [5]</ref>

Competing technologies

HVD is not the only technology in next-generation, high-capacity optical storage media. InPhase Technologies has developed a holographic format they call Tapestry Media, capable of storing up to 1.6TB with a data transfer rate of 120 MB/s. Hitachi Maxell, Ltd. plans to enter the market by offering 300GB discs with a data transfer rate of 20 Mbit/s. With such a high end storage capacity, it would seem like a better technology than either HD DVD or Blu-ray Disc. However, the reader currently costs approximately US$15,000, and a single disc currently costs approximately US$120, and by 2010, will cost about US$100. The market for this format is currently not the common consumer, but is instead for those with very large storage needs. [6].

The HVD Alliance

The HVD Alliance is a coalition of corporations purposed to provide an industry forum for testing and technical discussion of all aspects of HVD design and manufacturing. By cooperating, members of the Alliance hope to expedite development and engender a market receptive to HVD technology.

As of February 2006, the HVD Alliance comprises these corporations:

Proposed standards

Ecma, along with the TC44 committee, will work on standards for 200-Gbyte holographic versatile disk (HVD) cartridges, 100-Gbyte HVD read-only disks, 30-Gbyte HVD cards and an optional provision for HVD-ROM disks. [7]


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See also

External links

This article is licensed under the GNU Free Documentation License. It uses material from the article: Holographic Versatile Disc on the WIKIPEDIA

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