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INTRODUCTION>>Devices that use light to store and read data has always become the

backbone of our data storage system for nearly two decades. Each timeyou access towards the large repository of digital information.

>> All the way to the mammoth 320 GB hard disk drives available today, weuse also optical devices such as CDs ,DVDs and Blue-Ray Disk .

>> With the promise of tomorrow's operating systems and create new era ofstorage via laser, the demands of being able to quickly store and retrieveenormous quantities of data are ever increasing.

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DEFINITION >>Holographic memoryis a technology that can storeinformation at high density inside crystals or

photopolymers.

>>Conventional memories use only the surface to store thedata. But holographic data storage systems use thevolume to store data.

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BASIC PRINCIPLE OF HDSS>>A hologram is a block or sheet of photosensitive material which records

the diffraction of two light sources.

>>To create a hologram, laser light is first split into two beams:1.Source beam- Data signal

2.Reference beam- Carrier signal

>>And both intersect on hologram.

>> While reading data we hit Reference signal on exact angle which wasuse during writing process.

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BASIC COMPONENTS OF HDSS>> BLUE-GREEN ARGON LASER

>>POLARIZING BEAM SPLITTERS

>>MIRRORS TO DIRECT THE LASER BEAMS

>>SPATIAL LIGHT MODULATOR (SLM)>> LENSES TO FOCUS THE LASER BEAMS

>> PHOTO -POLYMER

>>CHARGE-COUPLED DEVICE (CCD )

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In a holographic memory device, a laser beam is split in two,

and the two resulting beams interact in a crystal medium tostore a holographic recreation of a page of data.

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Implementation

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WORKING OF HDSS

WRITING DATA ON RECORDING MEDIUM

>>Light from a single laser beam is split into two beams, the signal beam(which carries the data) and the reference beam. The hologram is formedwhere these two beams intersect in the recording medium. The objectbeam, gets expanded so that it fully illuminates a spatial light

modulator (SLM)

>>The object beam finally interacts with the reference beam inside aphotosensitive crystal causing a holograph to be stored

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Writing Data on HOLOGRAM

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READING DATA FROM HOLOGRAM

>>When reading out the data, the reference beam has to hit the crystal atthe same angle that's used in recording the page. The storedinterference pattern diffracts the reference beam's light so that itreconstructs the checkerboard image of the light or dark pixels.

>> The image is directed upon a charge-coupled device (CCD) sensorarray that reads the data in parallel, and it instantly captures theentire digital page. The binary information can now be read fromthis CCD and the originally stored data is retrieved.

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Reading Data from HOLOGRAM

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MULTIPLEXING>>The method of storing multiple pages of data in the

hologram is called Multiplexing.

WAVELENGTH MULTIPLEXING ANGULAR MULTIPLEXING

SPATIAL MULTIPLEXING> PERISTROPHIC MULTIPLEXING> SHIFT MULTIPLEXING

PHASE ENCODED MULTIPLEXINGMULTIPLEXING COMBINATIONS

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ADVANTAGES OF HDDS>> With three-dimensional recording and parallel datareadout, holographic memories can outperform

existing optical storage techniques. In contrast to thecurrently available storage strategies.

>>holographic mass memory simultaneously offers highdata capacity and short data access time (Storagecapacity of about 1TB/cc and data transfer rate of 1billion bits/second).

>> While a defect in the medium for disk or tape storagemight garble critical data, a defect in a holographicmedium doesn't wipe out information

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DISADVANTAGES OF HDDS>> Manufacturing cost HDSS is very high and there is a lack ofavailability of resources which are needed to produce HDSS.

>> A difficulty with the HDSS technology had been the destructivereadout. The re-illuminated reference beam used to retrieve therecorded information, also excites the donor electrons anddisturbs the equilibrium of the space charge field in a manner thatproduces a gradual erasure of the recording.

>> You would be unable to locate the data if theres an error ofeven a thousandth of an inch.

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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 theprocesses of finding patterns in large amounts of data. Datamining is used greatly in large databases which hold possiblepatterns which cant be distinguished by human eyes due tothe vast amount of data.

>> The many advances in access times and data storage capacitythat holographic memory provides could exceed conventionalstorage and speedup data mining considerably.

>> Another possible application of holographic memory is in petflop computing and most common application isHOLOGRAPHIC VERSATILE DISK (HVD).The future of digitaldata storage technology.

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>>Spatial Light Modulator (SLM)

Spatial light modulator is used for creating binaryinformation out of laser light. The SLM is a 2-D plane,

consisting of pixels, which can be turned on and off tocreate 1s and 0s. An illustration of this is a window and a

window shade. It is possible to pull the shade down overwindow to block incoming sunlight.

http://wiki/Image:HVDstruct.pnghttp://wiki/Image:Hvd_disc.jpg

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HVD

Holographic Versatile Disc structure1. Green writing/reading laser (532 nm)2. Red positioning/addressing laser (650 nm)3. Hologram (data)

4. Polycarbonate layer5. Photo polymeric layer (data-containing layer)6. Distance layers7. Dichotic layer (reflecting green light)8. Aluminum reflective layer (reflecting red light)9. Transparent base

http://wiki/Image:HVDstruct.pnghttp://wiki/Image:HVDstruct.pnghttp://wiki/Image:Hvd_disc.jpg

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Capacity

Writing/ReadingSpeed

DiscsApprox.

Cost

RecordablePlayerApprox.Cost

HolographicVersatile

Discs(HDSS)

HVD

300 GB1.6 TB 1 GB/s $120 $3000

Blu-rayDiscs

BD25 GB50 GB

36.5

Mb/s $18 $2000Digital

Versatile

Discs

DVDHD-DVD

5 GB30 GB

36.5

Mb/s $10 $2000Compact

Discs CD783 MB1.3 GB

27.5

Mb/s $4 $200

Comparison of data storage devices

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CONCLUSION

>> The future of HOLOGRAPHIC DATA STORAGE

SYSYEM is very promising. The page access of datathat HDSS creates will provide a window into nextgeneration computing by adding another dimension tostored data

>> It will most likely be used in next generationsupercomputers where cost is not as much of an issue.

>> However, many advances in optical technology andphotosensitive materials need to be made before we

find holograms in our computer systems. Thus we cansay that it is new ERA of digital data storage fromLASER.

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