Holographic Data Storage Systems

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HOLOGRAPHIC DATASTORAGE SYSTEM (HDSS)


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INTRODUCTION

Magnetic and conventional optical data storagetechnologies are approaching physical limitsbeyond which individual bits may be too smallor too difficult to store.

Holographic memory is developing technologythat has promised to revolutionalise thestorage systems.

It can store data upto 1 Tb in a sugar cube

sized crystal. Data from more than 1000 CDscan fit into a holographic memory System.

Holographic data storage is an approach ofstoring information throughout the volume of amediumnot just on its surface. It is based onthe principle of holography.

With the rapidly increasing demand for


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WHY DO WE NEED THIS?

For Internet applications alone,industry estimates are that storage

needs are doubling every 100 days-Nelson Diaz, Lucent Technologies

Optoelectronics Industry andTechnology Development Association

projects that by the year 2010, astorage system serving an average LANwill need 10 TB and a WAN server willrequire 100 TB to 1 petabyte ofstorage

- Red Herring


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WHATIS HOLOGRAPHY?

Holography is a technique of recordingpatterns of light to produce three

dimensional object.

Holographic memory is a technique thatcan store information at high densityinside crystals or photopolymers.


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The holographic memory system is made upof the following basic components:

Blue-green argon laser

Beam splitters to spilt the laser beam

Mirrors to direct the laser beams

LCD panel (spatial light modulator)

Lenses to focus the laser beams

Lithium-niobate crystal or photopolymer

Charge coupled device camera(CCD)

COMPONENTSOF HOLOGRAPHIC

MEMORY


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OVERVIEWOFHOLOGRAPHIC DATASTORAGE


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THE PRACTICAL SETUP


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Laser light is agreen 514.5-nmline of an argon-ion

laser.The system is

equipped with anargon (514.5-nm)or a krypton (676-nm) laser

Optical powerdelivered to theapparatus prior totheobject/reference

beam splitter is asmuch as 100-400

THE GREEN ARGON LASER


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A spatial lightmodulator is usedfor creating binaryinformation out oflaser light. The SLMis a 2D plane,consisting of pixelswhich can be turnedon and off to createbinary 1s and 0s.

WHATIS SLM?


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CCD - Charge CoupledDevice.

CCD is a lightsensitive device.

CCD converts pixels inimages into electriccharge.

CCD contains aseparate value foreach colour.

WHATIS CCD ?


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Chemical Formula- LiNbO3.

It has high photorefractive sensitivity &stability.

It has trigonal structure.

Molecular weight - 147.9.

Band gap - 4eV.

ABOUT LITHIUM NIOBATE

CRYSTAL


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Unlike magnetic storagemechanisms which store data on

their surface, holographic memoriesstore information throughout theirwhole volume.

This method of storing multiple

pages of data in the hologram iscalled multiplexing.

MULTIPLEXING TECHNIQUE


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There are SIX types of multiplexing

Angular Multiplexing Wavelength Multiplexing

Spatial Multiplexing

Peristrophic Multiplexing Shift Multiplexing

Phase-Encoded Multiplexing


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In holographic data storage, an entire page ofinformation is stored at once as an opticalinterference pattern within a thick,

photosensitive optical material.

STORAGE INSIDETHE

PHOTOSENSITIVE MEDIUM


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Data stream is sent to the SLM as0s and 1s.

Forms a checkerboard pattern

1s transmit light, 0s block light

Beam is split

Light passing through SLM is the signal (object)

beam

Reflected beam is the reference beam

Beams interfere in the medium toproduce hologram much like

before

RECORDING


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Beam no longer split

Reference beam is diffracted off therecorded grating (hologram)

Reconstructs matrix

Projected using optic onto CCD

Converts into data stream

READING


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PC with a holographic technology platform(HoloPCs)will be able to access data more rapidly

and in a qualitativelydifferent manner than conventional PCs.

Two-dimensional data saving systems suchas CDs and DVDs record and retrieve filesin a serial fashion -- one bit at a time.Holographic data systems retain and

retrieve data in parallel, a total (million- bit)page of files at a time.

The interface of holography and roboticsmay make holobots that learn throughcreative identification of useful patterns inbig quantities of files.

ADVANTAGES


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Manufacturing cost HDSS is very highand there is a lack of

availability of resources which areneeded to produce HDSS.

Holograms appear dimmer becausetheir patterns must share the material's

finite dynamic range. Writes in the same fashion can degrade

previous writes in the same region ofthe medium.

DISADVANTAGES


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An HVD (holographic Versatile Disc), aholographic storage media, is an advanced

optical disc thats presently in thedevelopment stage.

An HVD would be a successor to todaysBlu-ray and HDDVD technologies.

APPLICATION: Holographic

Versatile Disc(HVD)


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Parameters DVD BLU-RAY HVD

Capacity 4.7GB 25GB 3.9TB

Diskdiameter

120mm 120mm 120mm

Hard coating no Yes Yes

Laser wavelength wave

650 nm(red)

405 nm(blue)

532 nm(green)

Data TransferRate (raw

data)

11.08mbps36 mbps 1gbps

COMPARISON


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The future of holographic memory isvery promising. The page access of data

that holographic memory creates willprovide a window into next generationcomputing by adding another dimensionto stored data.

Holographic memory will most likelybe used in next generation supercomputers where cost is not as much ofan issue.

CONCLUSION


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Holographic Data Storage Systems

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