Contents1. Introduction.2. What is Holographic memory?3. What is HVD?4. Basic Principle.5. Structure of HVD.6. Components of HVD.7. Spatial Light Modulator8. How HVD Works? i. Recording Data. ii. Writing Data.9. Comparison.10. Advantages of HVD.11. Disadvantages of HVD.12. Possible Applications.13. Interesting Facts.14. Conclusion.
IntroductionAs computer systems continue to become faster,they will need a way to access larger amounts of datain shorter periods of time.Holographic memory is a three-dimensional datastorage system that can stored information at highdensity inside the crystal or photopolymer.Hence holographic storage system has the potentialto became the next storage generation overconventional storage system.
What is Holographic MemoryIt is a memory that can store information in form of holographicimage. It is a technique that can store information at high density insidecrystals or photopolymers.Conventional memories use only the surface to store the data. Butholographic data storage systems use the volume to store data. It hasmore advantages than conventional storage systems. It is based on theprinciple of holography.Unlike magnetic storage mechanisms which store data on theirsurfaces, holographic memories store information throughout theirwhole volume. After a page of data is recorded
Holographic Versatile DiscHolographic Versatile Disc (HVD) is an optical disc technology stillin the research stage which would hold up to 3.9 terabyte (TB) ofinformation.It employs a technique known as collinear holography, whereby twolasers, one red and one blue-green, are collimated in a single beam.The blue-green laser reads data encoded as laser interference fringesfrom a holographic layer near the top of the disc while the red laser isused as the reference beam and to read servo information from aregular CD-style aluminum layer near the bottom.
Holographic Versatile Disc These discs have the capacity to hold up to 3.9 terabyte (TB) of information, which is approximately 5800 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 standard computer hard drives as of 2007. The HVD also has a transfer rate of 1gigabyte/s .
BASIC PRINCIPLEA hologram is a block or sheet of photosensitive material whichrecords the diffraction of two light sources.To create a hologram, laser light is first split into two beams, a sourcebeam and a reference beam. The source beam is then manipulated andsent into the photosensitive material .Once inside this material, itintersects the hologram. Once a hologram is recorded it can be viewedwith only the reference beam. The reference beam is projected into thehologram at the exact angle and it was projected during recording. When this light hits the recorded diffraction pattern the source beam isregenerated out of the refracted light. An exact copy of the source beamis sent out of the hologram and can be read by optical sensors. Forexample a hologram that can be obtained from a toy store illustrates thisidea. Precise laser equipment is used at the factory to create thehologram.
HVD Structure 1. Green writing/reading laser (532 nm) 2. Red positioning/addressing laser (650 nm) 3. Hologram (data) 4. Polycarbon layer 5. Photo polymeric layer (data- containing layer) 6. Distance layers 7. Dichroic layer (reflecting green light) 8. Aluminum reflective layer (reflecting red light) 9. Transparent base
BASIC COMPONENTS OF HVDBLUE-GREEN ARGON LASERPOLARIZING BEAM SPLITTERSMIRRORS TO DIRECT THE LASER BEAMSSPATIAL LIGHT MODULATOR (SLM)LENSES TO FOCUS THE LASER BEAMSPHOTO POLYMERCHARGE-COUPLED DEVICE (CCD )
In a holographic memory device, a laser beam is split in two, and the two resulting beams interact in a crystal medium to store a holographic recreation of a page of data.
SPATIAL LIGHT MODULATOR (SLM) Translates electronic data (0s and 1s)into optical pattern of light and darkpixels. Data is arranged in an array similar toa checkerboard of usually 1M (million)bits. By varying the angle of the reference beam, wavelength or media position,many holograms can be stored in thesame volume of storage material.
WORKING OF HVD Writing Data The process of writing information onto an HVD begins with encoding the information into binary data to be stored in the SLM. These data are turned into ones and zeroes represented as opaque or translucent areas on a "page" -- this page is the image that the information beam is going to pass through.
1. Once the page of data is created, the next step is to fire a laser beam into a beam splitter to produce two identical beams. One of the beams is directed away from the SLM -- this beam becomes the reference beam. The other beam is directed toward the SLM and becomes the information beam.2. When the information beam passes through the SLM, portions of the light are blocked by the opaque areas of the page, and portions pass through the translucent areas. In this way, the information beam carries the image once it passes through the SLM.3. When the reference beam and the information beam rejoin on the same axis, they create a pattern of light interference -- the holography data. This joint beam carries the interference pattern to the photopolymer disc and stores it there as a hologram.
Reading Data1. In order to retrieve and reconstruct the holographic page of data stored in the crystal, the reference beam is shined into the crystal at exactly the same angle at which it entered to store that page of data.2. Each page of data is stored in a different area of the crystal, based on the angle at which the reference beam strikes it.3. During reconstruction, the beam will be diffracted by the crystal to allow the recreation of the original page that was stored.4. This reconstructed page is then projected onto the charge-coupled device (CCD) camera, which interprets and forwards the digital information to a computer.5. The key component of any holographic data storage system is the angle at which the second reference beam is fired at the crystal to retrieve a page of data. It must match the original reference beam angle exactly. A difference of just a thousandth of a millimeter will result in failure to retrieve that page of data.
COMPARISONParameters DVD BLU-RAY HVDCapacity 4.7 gb 25 gb 3.9 tbLaser wave length 650 nm 405 nm 532 nm (red) (blue) (green)Disc diameter 120 mm 120 mm 120 mmHard coating no yes yesData transfer rate (raw data) 11.08 mbps 36 mbps 1 gbpsData transfer rate (audio/video) 10.08 mbps 54 mbps 1 gbps
Advantages of HVD1. Resistance to damage - If some parts of the medium are damaged, all information can still be obtained from other parts.2. Efficient retrieval - All information can be retrieved from any part of the medium.3. These discs have the capacity to hold up to 3.9 terabyte (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 48 times the capacity of standard computer hard drives.4. The HVD also has a transfer rate of 1 gigabit/s.5. While reading a page the entire page of data can be retrieved quickly and at one time .
DISADVANTAGES OF HVDManufacturing cost HVD is very high and there is a lack of availability of resources which are needed to produce HVD. A difficulty with the HVD technology had been the destructive readout. The re-illuminated reference beam used to retrieve the recorded information, also excites the donor electrons and disturbs the equilibrium of the space charge field in a manner that produces a gradual erasure of the recording.You would be unable to locate the data if there’s an error of even a thousandth of an inch.
POSSIBLE APPLICATIONS Holographic memory systems can potentially provide the high speed transfers and large volumes of future computer system. One possible application is data mining. Data mining is the processes of finding patterns in large amounts of data. Data mining is used greatly in large databases which hold possible patterns which can’t be distinguished by human eyes due to the vast amount of data. The many advances in access times and data storage capacity that holographic memory provides could exceed conventional storage and speedup data mining considerably Holographic Versatile Disc (HVD) is an optical disc technology still in the research stage which would hold up to 3.9 terabytes (TB) of information
INTERESTING FACTS It has been estimated that the books in the U.S. Library of Congress, the largest library in the world , could be stored on six HVDs. The pictures of every landmass on Earth - like the ones shown in Google Earth - can be stored on two HVDs. With MPEG4 ASP encoding, a HVD can hold anywhere between 4,600-11,900 hours of video, which is enough for non-stop playing for a year.
ConclusionCapacity increased from 3.00GB to 3.9 TBNo need to turn over the CD,DVD,HD-DVD,etc.Three-dimensional data storage ,store information ina smaller space and faster data transfer times .The HVD playing device would have data rates 25times faster than todays fastest DVD players.