Holographic Versatile Disc
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 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 disks have the capacity to hold up to 3.9 terabytes (TB) of information, which is approximately eighty times the capacity of Blu-ray Disc. The HVD also has a transfer rate of 1 Gbit/s.
1. Green writing/reading laser (532nm)
2. Red positioning/addressing laser (650nm)
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
P. PIT
The HVD Alliance
The HVD Alliance is a group of companies that have banded together to provide a forum for testing and technical discussion of all aspects of HVD design and manufacturing, in the hopes of speeding development and creating a marketplace receptive to HVD technology. The current members of the HVD Alliance (as of October 2005) are:
- ALPS ELECTRIC Co., Ltd.
- CMC MAGNETICS CORPORATION
- EMTEC (MPO International)
- FUJI PHOTO FILM CO., LTD.
- KONICA MINOLTA OPTO. INC.
- LITE-ON IT CORPORATION
- MITSUBISHI KAGAKU MEDIA CO., LTD.
- NIPPON PAINT CO.,LTD.
- OPTWARE CORPORATION
- PULSTEC INDUSTRIAL CO.,LTD.
- Software Architects, Inc.
- SURUGA SEIKI CO., LTD.
- TOAGOSEI CO.,LTD.
Context
The books in one of the largest libraries in the world, the US Library of Congress, contain about 20 terabytes of text. Neglecting images, the content could be stored on a little more than 6 of these discs.
The article notes that the transfer rate is at an average of 1 gigabit/second. That is equal to 0.125 gigabytes/second, or 128 megabytes/second, which is a large leap over earlier storage mediums, whose transfer rates are generally measured in Kilobytes/second. In comparison, a 56x CD-ROM drive transfers at up to 8.4 Megabytes/second, and 16x-speed DVDs transfer at 22 Megabytes/second.
"By late 2001 the fastest high-performance drives were capable of an average latency of less than 3ms, an average seek time of between 4 and 7ms and maximum data transfer rates in the region of 50-60MB/s for EIDE and SCSI-based drives respectively." ---- These discs could transfer information twice as fast as modern day computer hard-drives.
At this rate it would take only 4.7 seconds to transfer an entire heavily compressed movie (600 MB) and about 8hours and 40 minutes to transfer over 820 DVD movies (roughly the storage capacity of the disk).