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InPhase Confidential

Outline of Presentation

• Introduction to HDS

• Introduction to Angle-Polytopic Phase Conjugate Architecture– Architecture and multiplexing– Professional Drive Diagram – Basic Drawing of optics – Shift invariant optical design– FRU

• Basic Servo techniques– Tolerances– Red Laser Disc Servo – Wobble servo

• Data Channel– Overview– Over-sampled Detection


Introduction to HDS

– Introduction HDS Technology


What is a Hologram ?


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 (Δn).

Mechanism

Example Media - conventional photopolymer media


Recording

Post cure

Precure of Media

Recording in Tapestry MediaRecording in Tapestry Media

Metered exposures translates the optical interference patterns into refractive index patterns in the media.

Post cure consumes any unreactedactive recording components in the

media.

Media is designed with to include inhibitor to preserve shelf life.

Precure consumes the inhibitor.

Bleach Bleach consumes the photoinitiator, the light trigger of the media.


Tapestry Media StructureTapestry Media Structure


How does Holographic Storage Work? Recording Data

Reading Data

Spatial Light Modulator

Data tobe stored

Data Pages

StorageMedium

Reference Beam

Laser

Laser Recovered Data

Reference BeamDetector

How are data recorded? The bits are encoded into an array of > 1 million pixels (page) recorded into the media via a laser.

How is capacity achieved?Hundred pages are recorded in the same location in the media, each with it’s own angular address.

How are transfer rates achieved?The entire array (page) is exposed for~ 2 milliseconds.

The media does NOT move while data are being recorded or recovered


Introduction to Angle-Polytopic Phase Conjugate Architectures

• Architecture and multiplexing• Professional Drive Diagrams and Pictures• FRU• Media Defect Detection


Standard Angle Multiplexing

SLM Lens Media

Data beam focusingthrough mediaReference beams

θn

Media

θ1

Wasted Media

Book volume


Angle Multiplexing Limits

0

20

40

60

80

100

120

140

160

10 400 800 1200 1600 2000

Thickness (microns)

Use

r C

apac

ity (G

B)

“Three-dimensional holographic disks" (H.-Y. S. Li and D. Psaltis) in Appl. Opt. vol 33, pp 3764-3774(1994)

Geometrical Storage Limit

d1

d2

0.8mm

1.5mm

ANGLE ONLY


Step1. Increase Density with Polytopic Recording

Traditional minimum book spacing

Books overlapped usingpolytopic recording


Basic Drive Recording & Recovery Optics

SLM data page of 1.4 mega pixels

Inverse read-out/data recovery

Camera

SLM

Each Page has unique address “angle” within a book

Media

p.1

p.2

Signal beam

Reference Beams


Minimize Book Volume by moving the focal point inside the media

10

5

0

-5

-10

1050-5-10

00thth OrderOrder

Nyquist filtering during recording

NyquistNyquistAreaArea


Drive Architecture - Write

SLM

CAMERA

POLYTOPIC FILTER

λ/2

λ/2λ/2

disk

Rm

Rm25°

50 m

Wiso

lator

+ sh

utte

r

Laser @ 405nm

CAMERAPHASEMASK


Drive Architecture - Read

SLM

CAMERA

POLYTOPIC FILTER

λ/2

λ/2λ/2

disk

Rm

Rm25°

50 m

Wiso

lator

+ sh

utte

r

Laser @ 405nm


DVT Drive Architecture

Fan FRU

Top

Bezel

Bottom

PCBA CageHood PCBA

OMA

Right Side

Loader

Laser FRU

Left Side

5 major subsystems– Loader– Laser FRU– Electronics– OMA– Enclosure


DVT OMA Optical Path:

Key:Pink = Laser FRUPurple = Laser DeliveryYellow = Beam DividerGreen = Reference PathLight Blue = Data PathRed = Cure

SLM

Phase MaskImager lens

CMOS Camera

LVR

Relay lens& polytopic filter

Galvo Group

Scanner Lens

FT Lens

Optical Divider

Phase Mask

FRU

4F relay system/laser delivery


The Phase Conjugate Advantage

• The phase conjugate geometry has a large advantage –perfect point spread function (PSF):– Aberrations removed during recovery.– Always diffraction limited regardless of optics used.

• Media shifts or different recovery optics (drive interchange) remove this advantage– Pixel wavefronts do not retrace their path. – No longer diffraction limited.

Camera

PBS

Reference Beam

λ/2 PlateHigh NA Lens

Holographic Media

Normal PSF PSF with Media Shift

Recovery


Isoplanatic Definitions• This is because Impulse Response is a function of field.

– PSF changes position and form as input changes position.– Most lenses are not spatially invariant.

• Isoplanatism Definitions:– Object Translation → Image Translation with no quality change– Object Rotation → Image Rotation with no quality change– Wavefront aberration in entrance pupil is constant– Wavefront aberration of image PSF is constant

• With typical lenses, isoplanatic patches are only slightly larger than PSF.


• Because Data Storage SNR is a function of PSF, the last definition can be modified.– SNR in system is constant in presence of finite shift or tilt of

conjugation optics.• InPhase has developed optical/holographic model to predicts SNR.

– Adapted as Zemax® plug-in.– Used during System Design to optimize performance

SNR / Optical Model for Design Optimization

Experimental SimulatedIntensity MapSNR / Distortion MapIntensity Map SNR / Distortion Map


Design Example #1

• Extremely Isoplanatic Storage Lens– 5 Elements– 1.7 mm radius field– 2.4 mm effective focal length

• ~3.0 mm Diameter Isoplanatic Patch– <1/50 RMS Wavefront variation in patch– Wavefront errors with shift are negligible over the patch.

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

RM

S W

avef

ront

Erro

r Diff

eren

ce

Field (mm)

Wavefront Error Variation


• Simulated Holograms written using plane wave reference.• Hologram read with position errors:

– 9.5º Tangential Media Tilt (400 μm Field Shift)– 80 μm Axial Shift– 80 μm Lateral Shift

• SNR Degradation is insignificant!

-1.5 -1 -0.5 0 0.5 1 1.50

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04RMS Wavefront Difference with 80 μm Axial Shift

Field (mm)

RM

S W

avef

ront

Erro

r Diff

eren

ce

-1 -0.5 0 0.5 10.04

0.045

0.05

0.055

0.06

0.065

Field (mm)

RM

S W

avef

ront

Erro

r Diff

eren

ce

RMS Wavefront Difference with 9.5 ° of tangential tilt

-1.5 -1 -0.5 0 0.5 1 1.50

0.005

0.01

0.015

0.02

0.025

0.03

Field (mm)

RM

S W

avef

ront

Erro

r Diff

eren

ce

RMS Wavefront Difference with 80 μm Lateral Shift

Lens Performance with Shift


-1.5 -1 -0.5 0 0.5 1 1.50.03

0.04

0.05

0.06

0.07

0.08

0.09RMS Wavefront with Assymetric Conjugation and 9.5 ° of Tilt

Field (mm)

RM

S W

avef

ront

Erro

r Diff

eren

ce

-1.5 -1 -0.5 0 0.5 1 1.50

0.01

0.02

0.03

0.04

0.05

0.06

0.07RMS Wavefront with Assymetric Conjugation and 80 μm of Lateral Shift

Field (mm)

RM

S W

avef

ront

Erro

r Diff

eren

ce

-1.5 -1 -0.5 0 0.5 1 1.50

0.01

0.02

0.03

0.04

0.05

0.06

Field (mm)

RMS Wavefront with Assymetric Conjugation and 80 μm of Axial Shift

RM

S W

avef

ront

Erro

r Diff

eren

ce

Design Example #2• Asymmetric Phase Conjugation

– Holograms written with 5 Element Lens read with simpler, 3 element, lens.

– Without media shift, perfect phase conjugation.– Hologram read with position errors:

• 9.5º Tangential Media Tilt < 0.1 Waves Error• 80 μm Axial Shift < 0.07 Waves Error• 80 μm Lateral Shift < 0.06 Waves Error


Conclusions

• With holographic storage systems, phase conjugate geometries have an advantage:– Always diffraction limited.

• This advantage is lost during drive to drive interchange or for media misalignments.

• Lens systems can be designed that are shift invariant due to isoplanatic Patches.– Patches where the PSF is spatially invariant.– Ideal for phase conjugate holographic storage systems.– Allows diffraction limited interchange.– Allows asymmetric recording / recovery systems.


Picture of FRU

Complete FRU With Laser On


Optical system configuration

• Features

A) High output power

B) Stable beam pointing

C) Stable mode performance

External Cavity

LD

Grating

Optical Output

LensAR-Coating

Wedge

mirror

Power sensor

Liner sensor Mode senor

LEDPSD

Wavelength sensor

anamorphic prism

Turn prism


Mode Sensor

• On-board FPGA calculates contrast ratio of fringes from an optical wedge• High Contrast <=> Single-mode operation• Mode servo added in last couple months – locks to stable mode using

mode sensor and current dither.

ThroughBeam to Power

Sensor

Linear Sensor Array

Wedge

Beamsplitter


Layer 0 Layer 1

Total capacity @ 65 kB per hologram, 320 pages/book, 15,262 data books = 317.4 GB- 1120 dummy books, dummy books are all black books in recovery- Disk is out of specification for edge wedge- Ave SNR ~4.4dB

Preliminary 300GB format (actually > 317GB)


Basic Servo techniques

– Tolerances

– Red Laser Disc Servo

– Wobble servo


± 0.2nmWavelength

±0.007°(±0.125°)

Tangential Tilt(w/ compensation)

Measured and Simulated Tolerances

+ 2.5 °CTemperature Detuning

± 0.015°Radial Tilt

± 0.020°Disk Rotation

(detrack)

± 50 μmShift in Z

(Media Focus)

± 25 μmShift in Y

(Radial detrack)

± 20/50 μmShift in X

(Tangential detrack)

± 0.007°Reference Beam Angle

± 75 μm

Tolerance Summary• Media Shift and Rotation

tolerances were– Experimentally determined– Simulated

• SNR Loss due to 3 Causes– Imperfect Phase Conjugation

• Correctable with lens design(≥ 3x Improvement)

– Bragg Mismatch• Based on NA and Media

Thickness– Crosstalk – No issue with this

geometry and density.


Red Laser Servo

Rotation servo pattern(inside data ID)

• Reads pattern with 850nm light• cos/sin pattern with home position• Resulting accuracy in theta is better than 4 micro degrees.


Sled Roller

• Pre-load the disk with sled roller wheel– Fix height of media in drive, set radial media pitch, improve vibration

performance

Disk

Spindle Roller @ R~64mm

Deflection

450um deflection

-0.05

-0.03

-0.01

0.01

0.03

0.05

0 20 40 60 80

Radius (mm)

Resi

du

al (m

m)

Series1


The Hologram Alignment Problem

• Problem: For recovery, holograms must be precisely aligned in 3 adjustable axes: φ, ρ & λ (reference beam angle, pitch and wavelength), and coarsely aligned in r & θ (disk coordinates).

• consider only φ, ρ & λ as critical

• Servo signals unavailable – must adjust based on data signal itself

• Must recover with ~1 exposure per hologram

• Transfer rate


Causes of Misalignment

Writing location

Rea

ding

loca

tion

-12 +12

-12

+12 Perfect recovery No temperature change

Hologram locations shift due to temperature change

Linear interpolation recovery

Error should be nearly quadratic across stack

Writing location

Rea

ding

loca

tion

-12 +12

-12

+12 Perfect recovery No temperature change

Hologram locations shift due to temperature change

Linear interpolation recovery

Error should be nearly quadratic across stack

( ) ( )( ) λφλ

φλλφφ

Δ+Δ+Δ+Δ+

Δ+Δ≈ΔΔΔ

FTEDTC

BTAT 2,,

• Environmental (especially temperature)

• Medium mis-registration

• Medium dimensional change (shrinkage)

• Drive component tolerances

• Other…

• Open-loop positioning is inadequate over all conditions even with pre-compensation


Measuring φ Alignment From SNR

• Signal-to-noise ratio is measured from known embedded bit patterns

• SNR degrades ~quadratically with φ mis-alignment

• Difference between 2 offset SNR values ∝ mean φerror

⎟⎟⎠

⎞⎜⎜⎝

⎛+−

=01

0110log20

σσμμ

SNR

φ

SNR

( ) ( )200 φφφ −−≈ CSNRSNR

0φ

0SNR

( ) ( )φ

φφφφφφΔ

Δ+−Δ−=−=

CSNRSNRerr

40

Single hologram SNR peak


Angle Wobble Servo

• Introduce small alternating angle offset (~±0.002o, ~3 % of spacing)

• Even and odd hologram SNRs will differ if not centered about peaks → SNReven

– SNRodd is angle error signal

• Use low-gain servo loop to determine sample angle of next hologram based on error signal

φ

Wobble servoSNR

evenodd odd even evenodd

SNReven‐SNRodd

…… ……

φ deviation


RLS Servo Loop

• Varying hologram SNR causes feedback signal to be noisy, P.I.D. controller performs poorly

• Use Recursive Least Squares Filter to estimate angle of next hologram based on (weighted) LS fit to past observations

• Can save RLS estimator state near beginning of book for use on next book

Hologram #

Est

imat

ed A

ngle

,

Previous hologram angles, φi + erri

Linear LS fit to previous holograms

LS estimate for next hologram


Simulated Wobble Servo

• Simulated holograms: SNR loss ~= 0.13 dB (nominal loss from wobble alone is ~0.03 dB)

0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 00

1

2

3

4

5

6S y n t h S N R s c a n

g a lvo

SN

RSN

R [d

B]

Peak SNRWobble SNR

Reference Beam Angle, φ


Gratings in k-space

LL

( )BAG kkKvvv

−±=

Akv

Bkv

Akv

Bkv

Real Space Momentum (k) Space


Holograms in k-space

SLM

HolographicMedia

Reference Beam

SLM

HolographicMedia

Data Page

• Each SLM pixel can be treated as a Plane Wave.• Pixels result in a manifold of grating vectors.

Real Space k-Space

Fourier Geometry:


Intensity Centroid Wobble

• Pitch misalignment causes Bragg mismatch of horizontal page edges, wavelength misalignment causes mismatch of vertical edges.

• Angle wobble causes Bragg-matched part to shift horizontally (pitch) or vertically (wavelength)

• Measure alternating intensity centroid shift to determine alignment error, correct with recursive least squares servo

1Pkv

2Pkv

xkv

zkv

ykv

Pitch misalignment shown


Wobble with Wavelength Error• When wavelength is de-tuned, wobbling the reference beam angle

changes location of Bragg-matched region

• Detect as change in y coordinate of intensity centroid between even and odd holograms


Wobble with Pitch Error• Pitch error causes vertically Bragg-matched stripe

• Detect as change in x coordinate of intensity centroid between even and odd holograms


Wobble Error Signal

• Note that small error causes large centroid shift: Bragg-matched locus movement varies inversely with error…

…but finite selectivity creates linear region. Wobble servo operates here.

regionerror

1

regionerror

1

error

measured error


Test Results

• Left Image is simulated centroid movement in SLM pixels with ±0.002° read-out reference wobble

• Right Image experimentally obtained from InPhase prototype

-0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04 0.05-100

-80

-60

-40

-20

0

20

40

60

80

100

Reference Beam Tilt (°)

Cen

troid

Shi

ft (S

LM P

ixel

s)

Simulated Centroid Shift for Hologram at 38 ° vs. Read Pitch over a ±0.002 Reference Angle Shift

Offset = -0.010Offset = -0.005Offset = 0.000Offset = +0.005Offset = +0.010

-4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5

-60

-40

-20

0

20

40

60

Pitch Corrector Angle (°)

Cen

troid

Shi

ft (P

ixel

s)

Centroid Shift for Hologram at 38 ° vs. Read Pitch over a ±0.002 Reference Angle Shift

Offset = -0.002Offset = 0.000Offset = +0.002

Simulated Experimental


Data Channel

– Overview

– Over-sampled Detection

– Logical Format /Data Architecture


Page-Oriented Optical Data Storage

M

L

1100001110101001

M

L

1100001110101001

SLM Image

Detector Image

Data

Data

2D coherent image recovered

Storage


Read

WriteEncode

FPGAFormatter SLM

Optical

Path

LASER

Laser

Controller

LASEROptical

PathCamera

Camera

FPGA

Channel

FilteringDecode

Buffer

RAM

Buffer

RAM

Buffer

RAM

Randomize dataBit-wise dispersal across pageReserve blocks for servo and channelECC encoding

Detection and EqualizationUn-disperse bitsECC decoding

Hardware and Software Versions

Holographic Data Channel

Outer Codes


Data Arraying- Codeword Bit Dispersal Across Page


Data Page

Header (multiple redundant copies)

Optical alignment features Reserve blocks(For calculatingpage metrics)

Highly randomized data,codewords distributed all througheach page for robustness


The Detector Alignment Problem

High SNR Low SNR

Pixel-Matched

Oversampled

High SNR

4X bandwidth (Nyquist)

SLMImage


Resampling Method

OversampledImage

FIRFilter

MeasureAlignment

ResampledImage


Measure Alignment - “Quiver” Method

Known Blocks

Alignment MapPatternMatch


Reserved Block Equalization

Patterns selected to reduce noise

PatternCross-Correlation

Central Peak Surrounding Null


Reserved Block Oversampling

Detect resampled version of pattern

(4/3 oversampling ratio)


Resampling Method

OversampledImage

MeasureAlignment

ResampledImage

FIRFilter


Linear Resampling Method

Apply FIR coefficients to detector window

Pixel Image of Interest

δy

δx

Detected Values


Determining Coefficients

Find MMSE coefficients over many neighborhoods:

minimizediswhere

w

ww

d

dd

n

2

16

2

1

2

1

d̂d

II

IIII

ˆ

ˆˆ

n,16n,1

2,1

1,161,21,1

−

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡

⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢

⎣

⎡

=

⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢

⎣

⎡

MOM

L

M

SNR:

Solution ( ) dIIIw TT 1−=

( ) ( )( ) ( )01

01

=+=

=−==

ddstdddstd

ddmeanddmeanQ

ˆˆ

ˆˆ


Linearizing the Coherent Response

Improve using magnitude instead of intensity1

1 V. Vadde, B. V. K. V. Kumar, Appl. Opt. 38, 4374-4386 (1999).


Choose Oversampling Ratio

1 1.2 1.4 1.6 1.8 21.5

2

2.5

3

3.5

4

4.5

5

5.5

6SNR vs. Oversampling Ratio

Linear Oversampling Ratio

10 lo

g10

(Q)

δX = δY = 0.5δX = δY = 0.25δX = δY = 0

SNR vs. Oversampling Ratio


Resampled Image Example

Original Detector Image Resampled Image

4/3 oversampled image


Additional Developments with Partners

HROM Device and Replication Technology

• Content Distribution• Backward compatible with SSM

Consumer Recordable Version

• Same Basic Technology as Professional Drive• Target slim height and BD compatible• Home Archive

Servo

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