In May of 2004 there was a breaking story:
Quantum trick may multipy CD capcityNow, almost a year and a half later, we have HVDs!
A fundamental law of classical physics has been broken by two teams of physicists who have linked particles of light together in a way that enhances its normal properties. Their method for 'entangling' photons could one day allow information to be more densely crammed and read from CDs and other memory devices. ( Read more... )
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.
So what does all of this mean for you normal people?
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 Discs. The HVD also has a transfer rate of 128 Megabytes/second. In comparison, CDs transfer at up to 8.4Mb/s and store 700MB and DVDs transfer up to 21.6Mb/s and store 4.5GB (standard, or 27GB with Blu-ray). So you could fit 213 full (standard) DVD movies on one HVD and it'll only take 998 seconds (about 16 minutes) to burn them all!
Holographic Versatile Disc structure
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
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