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Page 1
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
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
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InPhase Confidential
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.
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InPhase Confidential
Tapestry Media StructureTapestry Media Structure
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InPhase Confidential
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
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InPhase Confidential
Introduction to Angle-Polytopic Phase Conjugate Architectures
• Architecture and multiplexing• Professional Drive Diagrams and Pictures• FRU• Media Defect Detection
Page 9
InPhase Confidential
Standard Angle Multiplexing
SLM Lens Media
Data beam focusingthrough mediaReference beams
θn
Media
θ1
Wasted Media
Book volume
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InPhase Confidential
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
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InPhase Confidential
Step1. Increase Density with Polytopic Recording
Traditional minimum book spacing
Books overlapped usingpolytopic recording
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InPhase Confidential
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
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InPhase Confidential
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
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InPhase Confidential
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
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InPhase Confidential
Drive Architecture - Read
SLM
CAMERA
POLYTOPIC FILTER
λ/2
λ/2λ/2
disk
Rm
Rm25°
50 m
Wiso
lator
+ sh
utte
r
Laser @ 405nm
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InPhase Confidential
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
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InPhase Confidential
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
Page 18
InPhase Confidential
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
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InPhase Confidential
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.
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InPhase Confidential
• 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
• 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.
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InPhase Confidential
Picture of FRU
Complete FRU With Laser On
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InPhase Confidential
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
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InPhase Confidential
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
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InPhase Confidential
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
• 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.
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InPhase Confidential
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.
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InPhase Confidential
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
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InPhase Confidential
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
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InPhase Confidential
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
Page 35
InPhase Confidential
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
Page 36
InPhase Confidential
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
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InPhase Confidential
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
Page 38
InPhase Confidential
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
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InPhase Confidential
Gratings in k-space
LL
( )BAG kkKvvv
−±=
Akv
Bkv
Akv
Bkv
Real Space Momentum (k) Space
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InPhase Confidential
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:
Page 41
InPhase Confidential
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
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InPhase Confidential
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
Page 43
InPhase Confidential
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
Page 44
InPhase Confidential
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
Page 45
InPhase Confidential
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