volume holographic data storage1

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Volume Holographic Data Storage Volume Holographic Data Storage

With Doped High Quality OpticalWith Doped High Quality OpticalGlassGlass



Need For It:

This system can store up to 1 terabyte of

data in 1 cubic centimeter of recordingmedium.

The retrieval of data is faster since the laserbeams have no inertia .

The characteristics of the ideal optical

storage medium include high optical qualityand low scatter, a large refractive indexmodulation, high sensitivity, long shelf life andlow material costs.



To obtain a method of data storage whereTo obtain a method of data storage where the

wavelength of the light beam used to read thehologram is not restricted to the particularwavelength used to record the hologram.

To provide a method that allows a plurality of volumeTo provide a method that allows a plurality of volumeholograms to be recorded in a thick storage medium.holograms to be recorded in a thick storage medium.

To provide a method for creating a volume hologramTo provide a method for creating a volume hologramthat can be read many times without erasing.that can be read many times without erasing.

To provide a method for creating a volume hologramTo provide a method for creating a volume hologramwherein the wavelength of the light beam used towherein the wavelength of the light beam used toread the hologram is not restricted to the particularread the hologram is not restricted to the particularwavelength used to record the hologram.wavelength used to record the hologram.



INTRODUCTION:INTRODUCTION:

Volume holographic optical storage medium comprises a Volume holographic optical storage medium comprises a

doped optically transparent glass matrix having adoped optically transparent glass matrix having ascattering coefficient of less than 10scattering coefficient of less than 10 --55 cmcm --11 and exposingand exposingthe medium to an interference pattern created bythe medium to an interference pattern created byintersecting a spatially modulated object beam with aintersecting a spatially modulated object beam with areference beam.reference beam.



Preparation Of Glass Matrix:Preparation Of Glass Matrix:

The glass matrix may be dopedThe glass matrix may be doped

with any of the followingwith any of the followingembodiments : (1) nanocrystallineembodiments : (1) nanocrystallinesemiconductor particles (2) ansemiconductor particles (2) analkaline earth sulfide (3) ZnS andalkaline earth sulfide (3) ZnS and(4) Cu or Ce ions.(4) Cu or Ce ions.

The dopants used are sufficientlyThe dopants used are sufficientlysensitive to UV radiation so that sensitive to UV radiation so that only a low concentration of theonly a low concentration of thedopant is necessary to adequatelydopant is necessary to adequatelyrecord data.record data.

Moreover, the dopants are either inMoreover, the dopants are either innanocrystalline form, or else arenanocrystalline form, or else aresmall molecules or ions. Thus, light small molecules or ions. Thus, light scattering is minimized in thescattering is minimized in therecording and reading of storedrecording and reading of storeddata.data.

Erbium Doped

Glass Fiber



Reading And Writing Using Glass Matrix:Reading And Writing Using Glass Matrix:

The doped glass has the property that when it is irradiatedThe doped glass has the property that when it is irradiatedwith light having a wavelength of less than about 300 nm,with light having a wavelength of less than about 300 nm,the excitation energy is stored as trapped charges in thethe excitation energy is stored as trapped charges in the

glass.glass.

The trapped charges modify the complex index of refractionThe trapped charges modify the complex index of refraction

of the glass. This property allows the doped glass to beof the glass. This property allows the doped glass to beused in storing volume hologramsused in storing volume holograms



BRIEF DESCRIPTION OF THE DR AWINGSBRIEF DESCRIPTION OF THE DR AWINGS A more complete appreciation of the invention will be readily obtained A more complete appreciation of the invention will be readily obtained

by reference to the graph of measured diffraction efficiency vs.by reference to the graph of measured diffraction efficiency vs.exposure time for a 2 mm thick sample of europiumexposure time for a 2 mm thick sample of europium--doped glassdoped glassexposed to a single mode KrF excimer laser operating at 248 nm at aexposed to a single mode KrF excimer laser operating at 248 nm at a

repetition rate of 2 Hzrepetition rate of 2 Hz..



EMBODIMENTSEMBODIMENTS

FIRST: The volume holographicstorage medium is a glass

matrix doped withnanocrystallinesemiconductor particles andan activator. A

ctivators can be :1.Transition metals2.Lanthanides

SECOND: Here the opticallystimulable glasses are

typically prepared bydiffusing the dopants intothe glass matrix. Due tothis, the glass matrix maybe either porous orfused.Here any alkaline earthsulfide may be used asthe dopant .



THIRD:THIRD:

In this stage aIn this stage aglass matrixglass matrixincludes metalincludes metalsulphide and ansulphide and an

activator.Theactivator.Theactivator isactivator isemployed over theemployed over thesulphide so as tosulphide so as toget the diffusionget the diffusion

done.done.

FOURTH:

In this fourth andfinal embodiment,the glass matrixincludes Cu or Ce

dopants in theabsence of a metalsulfide component,or even in theabsence of any

sulfide component.



DOPING

These steps show how to dope a glass matrix:

Diffusion of dopants by

dipping in org /inorgsol-gels

Dried andactivated at

hightemperaturesusing glass

tubes in furnaces

The material of the four

embodiments may

be shapedafter the doping

Process sothat it is

suitable as avolume hologram

Contact with salt solution of dopant

DryingGetting metal

sulphideby adding sulphur

Glass tubeused tohold the

glass samplesduring activation

is a sourceof dopants.

The optical stimulableluminescence (OSL)

activity of fusedglasses may be

enhanced byrepeated heating



LIMITAT

ION

S:

LIMITAT

ION

S:

To cater the present day needs, additional requirementsTo cater the present day needs, additional requirementsare that:are that:

The glass starting material be limited to fused quartzThe glass starting material be limited to fused quartzand fused silica.and fused silica.

The concentration of dopant be kept low so that theThe concentration of dopant be kept low so that thedopant does not significantly reduce the transparency of dopant does not significantly reduce the transparency of

the glass.the glass.



CON

CLUSI

ON:C

ONCL

USI

ON:

A plurality of volume holograms may be recorded and A plurality of volume holograms may be recorded andread within the volume holographic optical storageread within the volume holographic optical storagemedium by techniques of angular and wavelengthmedium by techniques of angular and wavelength

multiplexing known in the art.multiplexing known in the art.

The enabling technologies for creating and readingThe enabling technologies for creating and readingvolume holograms and for storing and retrieving volumevolume holograms and for storing and retrieving volumeholographic high density data are well developedholographic high density data are well developed

..



REFERENCES:

Hill et al., "Photosensitivity in opticalfiber waveguides: . . . " A ppl. ys. Lett.,vol. 32(10), pp. 647-649, May 1978.Melles Griot Catalog 1995/1996, pp.48-2 to 48-5.Meltz, G., et al., "Formation of Bragg

gratings in optical fibers by atransverse holographic method" Opt.Lett., vol. 14(15) pp. 823-825, A ug.1989.Partovi, A . et al "Volume HolographicStorage in Hydrogen Treated

Germano-Silicate Glass" A

ppl. Phys.Lett. 64(4) (1994), pp. 821-823.

Huston, A .L. and Justus B.L."Photoreversible Birefringence inDoped Vycor Glass" Optics Letters,vol. 20, No. 9, May 1, 1995, pp. 952-954.

Partovi, A . et al, "VolumeHolographic Storage in Germano-Silicate Glass" CLEO '94,Summaries of Papers at theConference on Lasers and Electro-Optics, vol. 8 1994 Technical Digest

Series. Conference Edition (Cat. No.94CH3463-7), p. xvi+448, 7-8.Erdogan, et al, "Volume Gratingsfor Holographic Storage A pplications Written in High-QualityGermanosilicate Glass" A pplied

Optics, vol. 34,N

o. 29, Oct. 10,1995, pp. 6738-6743.

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