high density, high performance, holographic data …(1) presented at the thic meeting at the naval...

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Presented at the THIC Meeting at the Naval Surface Warfare Center Carderock, 9500 MacArthur Blvd

West Bethesda MD 20817-5700October 3, 2000

High Density, High Performance, High Density, High Performance, Holographic Data Storage:Holographic Data Storage:

Viable at last?Viable at last?William L. Wilson

Photonics Materials Research DepartmentBell Laboratories, Lucent Technologies

Murray Hill NJ 07974Phone:+1-908-582-7919, Fax:+1-908-582-3958

E-mail: [email protected]

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• Introduction to holography• Optical storage via volume holography• Technology review and current status• Conclusion and prognosis

High Density, High Performance, High Density, High Performance, Holographic Data StorageHolographic Data Storage::

Viable at last?Viable at last?William L. WilsonPhotonics Materials Research DepartmentBell Laboratories, Lucent TechnologiesMurray Hill, NJ 07974

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SystemKevin CurtisWilliam WilsonMike TackittAdrian HillTom RichardsonPeter LittlewoodPartha MitraScott Campbell

Material Lisa DharAlex HarrisMarcia SchillingHoward KatzMelinda SchnoesArturo HaleCarol BoydAdam Olsen

Partial List of ContributorsPartial List of Contributors

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Holography PrimmerHolography Primmer

*Total recording of the optical field

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Holographic Recording FundamentalsHolographic Recording Fundamentals

• Parallel readout of data - fast rates• Multiplexing - much greater density

The Holographic “Advantage”The Holographic “Advantage”

Storage of many holograms in the same volume with selective addressing of the individual holograms generates density!!

•Angle Multiplexing*•Wavelength Multiplexing*•Shift Multiplexing*•Peristropic Multiplexing•Phase-code Multiplexing*

*Most techniques are based on or drivenby the Bragg effect or strongly enhanced by Bragg processes

Issue: How do we access each hologram independently?(Selectivity, allows us to exceed the diffraction limit)

The Bragg EffectThe Bragg Effect

Constructive interferenceachieved at specific θ

for a given Λ

The higher the number of scattering planes,The finer the angular or wavelength resolution!!

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Bragg Selectivity of Volume HologramsBragg Selectivity of Volume Holograms

Angular Selectivity of 38 um thick photopolymer film

•• change anglechange angle•• change wavelength change wavelength

-2 -1 0 1 2

0.0

0.2

0.4

0.6

0.8

1.0

Deviation from Bragg (Degrees)

Diff

.Int

(A

U)

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Promise of Holographic StoragePromise of Holographic Storage

The Dream? Maximum density >1bit/λ3

**The Library of Congress on a sugar cube!!**The Library of Congress on a sugar cube!!**The Library of Congress on a sugar cube!!**The Library of Congress on a sugar cube!!**The Library of Congress on a sugar cube!!**The Library of Congress on a sugar cube!!**The Library of Congress on a sugar cube!!**The Library of Congress on a sugar cube!!

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We are not the First!We are not the First!

Bernhard Hill, Philips LabsBernhard Hill, Philips Labs“Advances in Holography”, 1976“Advances in Holography”, 1976

“The Essential Components of a Block“The Essential Components of a Block--organized Holographic Memory”organized Holographic Memory”

44A laser SourceA laser Source44A laser beam deflector*A laser beam deflector*44A fly’s eye lens A fly’s eye lens 44A page composerA page composer44A detector arrayA detector array44A storage matrix**A storage matrix**

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Past Problems with HolographyPast Problems with Holography

• Material - No acceptable material and mediarequirements were ill defined.

• Methods - Complex and difficult, limited density

• Lasers - Extremely costly and unreliable

• Detector - Cost and performance

• SLM - Performance at issue, (frame rates, throughput, etc.)

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But we can’t ignore the technology!But we can’t ignore the technology!

1980 1985 1990 1995 2000

1

10

100

1000

10000

Cap

acity

, GB

ytes

/(51 / 4"

Dis

k)

Library of Congress

100 Movies

1 Movie (DVD)

1996 CD-ROM

Characteristics: High Transfer Rates - > 1GB/secHigh Density - initially 500 Gbytes on a 5-1/4 formatLow Cost/MB - comparable to tapeWrite Once, Removable storage - WORMParallel Read/Write - page access instead of bit access

Holographic StorageHolographic Storage

Industry TrendIndustry Trend

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Holographic Recording FundamentalsHolographic Recording Fundamentals::TranslationalTranslational/Shift Multiplexing/Shift Multiplexing

Material

Object

ReferenceHologram formsin Overlap Region

• Parallel readout of data - fast rates• leverages current technologies

Shift direction

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New Method: Correlation Multiplexing (CM)New Method: Correlation Multiplexing (CM)

• Simple to implement• Selectivity independent of material thickness• ~5x density over other holographic approaches • Written 16,000 ~300Kbit holograms at 350 bits/um2

-10-5

05

10 -10

-5

05

10

0

20

40

60

Diffr

acte

d In

tens

.

∆Y (µm

)

∆X (µm)

Signal Beam

Multiplex by moving the mediumReference

Beam

Selectivity Map

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Array of Stored HologramsArray of Stored Holograms

∆x

30µmHologramDia. ~3mm

30µm

∆y

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-75 -50 -25 0 25 50 75

75

50

25

0

-25

-50

-75

∆X Microns

∆Y M

icro

ns

0.5 0.6 0.7 0.8 0.9 1.0

Intensity (arb. units)

Hologram FidelityHologram Fidelity

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500 1000 1500 2000 2500 3000

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

< η > ~ 10-5

~50% Overhead for Channel Modulation and ECCRaw BER O~10-5

ampl

itude

SN

R

Hologram number

First hologram

Last hologram

Density:Density:~48 channel bits/~48 channel bits/µµmm22

Data Stored and Recovered Data Stored and Recovered from Polymeric Mediafrom Polymeric Media

Methods, Methods, a Prognosisa Prognosis

•New innovative simple methods developed!•High density recording demonstrated•High fidelity holograms recorded

Physics not our problem!!

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Dynamic Range - High storage densities & rapid read rates

Photosensitivity - Rapid write rates

Millimeter Thickness - High storage densities

Dimensional Stability - High fidelity data recovery

Optical Flatness - High fidelity imaging of data pages

Low Scatter - Low levels of noise in data recovery

Processing - Heat/Solvent Free

Non-volatile readout

Long shelf-life of media

Long archival life of stored data

Environmental/thermal stability

Requirements for holographic storage media

High Storage Capacity

Rapid Write/Read Rates

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Past Candidates for Materials for Holographic Data Past Candidates for Materials for Holographic Data StorageStorage

LiNbO3Volatile ReadoutLow photosensitivityLow dynamic range

Photorefractive polymersVolatile ReadoutRequirement of poling voltages (large)Low photosensitivity

Photopolymers . . .

What’s the problem?

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Material Dynamic Range is King!Material Dynamic Range is King!

**But an overall system view is Queen!!

Materials Systems

•System capacity determines the density needed a fixed media size•Density at fixed media size provides M•Power budget effects minimal ηηηη•Signal detection floor effect limiting ηηηη

You need to decide what to build!

M/# as Standard MetricM/# as Standard Metric

Can be used as a empirical parameter for any material system!

η = (M/#/M)2

*a much better metric for storage!

In general, for all systems the diffractedintensity of an ensemble of holograms

written under identical conditionsscales as

1/M2

The M-number allow us to quantify a materialsutility as a storage media.

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Our View: Go WORM/ROMOur View: Go WORM/ROM

Punt read/write, and try to solve other problems with the technology

• Concentrate on a WORM or ROM basedsystem to shake out technology

Materials for our assessment: PhotopolymersMaterials for our assessment: Photopolymers

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System consists of monomers dissolved in a matrix.

Holographic exposure produces a spatial pattern of photoinitiated polymerization.

Concentration gradient in unreacted monomers induces diffusion of species.

Diffusion produces a compositional gradient, establishing a refractive index grating.

• High photosensitivity

• Permanent holograms

• Low cost

Mechanism

Advantages

Grating Formation in Conventional Photopolymer SystemsGrating Formation in Conventional Photopolymer Systems

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0

1

2

3

4

5

6

7

8

9

10Dynamic Range in Bell Labs LowDynamic Range in Bell Labs Low--TTgg Photopolymer Media:Photopolymer Media:

Date

M#

@ 2

00 µµ µµ

m

6/95

9/95

8/97

1/98

7/96

Goal: M# = 6 @ 200 µm( M# = 30 @ 1 mm)

Measurements performed in materials exhibiting 0.3% shrinkage during recording

3/98

Moore’s Law

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Interferogram of aPhotopolymer-Based Disk

Data page is imaged through sample with a

raw BER ~ 1x10-6.

Optical Quality in LowOptical Quality in Low TTgg Photopolymer MaterialsPhotopolymer Materials

/cm flatness achieved in 1 mm thick media 3’’x3’’λ10

100 Å

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Optical Quality: Pixel Matching with Low Bit Error Rates

-0.5 0.0 0.5 1.0 1.5 2.00

50

100

150

Num

ber o

f Pix

els

Normalized Pixel Intensities

-0.5 0.0 0.5 1.0 1.5 2.01

10

100

Num

ber o

f Pix

els

Normalized Pixel Intensities

Transmitted 800x600 data page

Expanded view of corner pixels

Histogram of pixel intensities, a measure of fidelity of data recovery.

Raw BER ~ 10-6

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Demonstrated Density in Photopolymer MediaDemonstrated Density in Photopolymer Media

Jan '96Jul '96

Jan '97Jun '98

Jul '98Aug '98

0.01

0.1

1

10

100

Den

sity

(bits

/µµ µµm

2 )

0.01

0.1

1

10

100

GB

ytes

/ (5

1 / 4" D

isk)

Channel DensityUser Density - Material 1User Density - Material 2

CD-ROM user density

(0.4 bits/mm 2)

DVD user density

(4.4 bits/mm 2)

New Material and

System Development

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WORM Media Capabilities - 5.25” diskCurrentMaterial(650 nm,

50 mW laser)

CurrentMaterial(532 nm,

50 mW laser)

CurrentMaterial(425 nm,

15 mW laser)

User Capacityper disk(channel density)

150 GB(106

Gbits/in2)

250 GB(175

Gbits/in2)

400 GB(300 Gbits/in2)

Write Rate 20 MB/sec 23 MB/sec 20 MB/sec

Read Rate 70 MB/sec 64 MB/sec 40 MB/sec(limited by

laser power)

Conclusions

Design, fabrication, & demonstration of high-performance photopolymer media for high density holographic data storage

!!!! High dynamic range, high photosensitivity with controlled recording-induced dimensional change

!!!! Optically flat, millimeter-thick, low scatter formats

!!!! Demonstrated high density digital data storage capabilities

Currently in program with Imation Corporation to further jointly develop the photopolymer media.

Materials, Materials, a Prognosisa Prognosis

•New strategy developed!•All issues on the table!•High M# media in hand! •Requirements out in the open•High density digital recording demonstrated•Digital data recovered at low BER, (10-5)

*Still the key problem, but on the run!!

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Component SummaryComponent Summary

• SLM - DMD Status– Fixed Problems with windows– 2,000 frames/sec– 80% light throughput– Contrast, ~1000:1– 800x600 pixels

• Detectors - CMOS Cameras – Custom detector functioning– Cheaper to produce than CCDs

=>$300 going to $30– Lower power, Less heat, Lower noise

• Laser - uchip/small cavity– Tested Uniphase and Micracor models– Cost, ~$2K going to $20– High volume is possible– Power, 200-600mW

Components, Components, a Prognosisa Prognosis

•All driven by other technologies!•SLM a commercial product•Camera soon to be a commercial high volume item

Only laser at issue, problem: price!!

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DEMO: System ArchitectureDEMO: System Architecture100mW laser

SLM

Stages & Sample

CMOSCamera

HOE for Reference 1 x 2 foot area

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System RisksSystem Risks

• Engineering and Drive Design• Long term life issues for Media and

Components• Market

If you build it will they buy???

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Past Problems with HolographyPast Problems with Holography(Current Status)(Current Status)

• Material - Two chemistry materials class has been developed, study of issues relevant to manufacture underway

• Methods - An array of simple, high density method developed. A compact demonstration device built, (1ft x 2ft).

• Laser - Moderate to low cost options coming on line.

• Detector - Optimal device type in hand.

• SLM - High throughput, fast frame rate devices available.

high density, high performance, holographic data …(1) presented at the thic meeting at the naval...

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