홀로그램저장재료. National Creative Research Center for Active Plasmonics Applications Systems

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Erick O’Brien’
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1 홀로그램저장재료

2 Holographic materials Material Reusable Processing Type of Exposure Spectral Resol. Max. diff. hologram (J/m2) sensitivity (lim./mm) efficiency Photographic emulsion Dichromated gelatin Photoresists Photopolymers Photochromics Photothermo -plastics Photorefractive No No No No Yes Yes Wet chemical Wet chemical Wet chemical Post exposure None Charge and heat Amplitude Phase Phase Phase Phase Amplitude Phase Uv-500 Uv > > (bandpass) LiNbO 3 Yes None Phase > Bi 2 SiO 20 Yes None Phase >

3 Holographic storage media parameters Optical quality For distortion-free imaging of the input data to the detector Storage medium is also one optical component Intrinsic light scattering: signal level minimum Sensitivity (Refractive index modulation) / (absorbed fluence) Dynamic range (M/#) Total response of the medium divided among many multiplexed holograms Absorption Diffraction efficiency & selectivity Volatility Dark decay (archival problem) and readout erasing

$+ + - Photorefractive crystal Crystal LCD CCD$ ++ ++ ++ -- -- ++ ++ ++ ++ -- -- ++ ++ ++ ++ -

++ ++ ++ -- -- ++ ++ ++ ++ -- -- ++ ++ ++ ++ -

4 + + - Photorefractive crystal Crystal LCD CCD 불균일한빛광이온화 I(x) Reference wave 확산트랩에서의재결합 자유전하밀도고정전하밀도 x x x 전기장 E(x) x 상대적굴절률격자 n(x) x

5 Photopolymer () Cover sheet PVC 60.9 µm lights Polymer layer 20.0 µm Base sheet Mylar 50.8 µm M M Binder-rich area (Low refractive index) Mixture of Sensitizing dyes, Initiators, Monomers, Polymeric binder Photopolymer-rich area (High refractive index)

6 Photopolymer (2) Shrinkage effect Dynamic range

7 홀로그램다중화

8 Multiplexing techniques Angle multiplexing Wavelength multiplexing Spatial & angle multiplexing Phase-code multiplexing Shift multiplexing Spatial & shift multiplexing

9 Hologram reading Weak scattering of volume dielectric grating???? ε r? Wave equation (vectorial, EM) ik g r ε ( r ) = ε o + ~ ε ( r ) e ( k ) E = U ( r )E ~ ε r ik g r U ( r ) = e ik g + K g K ε ( ) { ( ) k } 2 o g E i = e ik r eˆ E i Holograms in HDS; weak volume gratings st Born approximation i E ( d ) ε R * S S ' d ~ ε RS E E s ' * ' dr ~ SR Rr st Born approx. (single scattering) iki r i = e eˆ ik r r ' ( d ) e ~ i ' ( k ) i i 3 ( r ) = s( k ) d r' ε ( r ) = 4π r r ' 2 + K k eˆ ( K eˆ )( k ) g i ε Correlation! o g i( K g + ki ) r ' e

10 Selectivity Multiplexing unit detune

11 Phase matching condition Grating recording Bragg-matched reconstruction Bragg-mismatch: angle detune Bragg-mismatch: wavelength detune

12 공간광변조기

13 Spatial Light Modulator (SLM) LCD modulator Digital micromirror modulator

14 DMD 의구조및광학구성 DMD structures TIR prism for DMD

15 코딩

Coding Modulation codes For binary detection; balanced block code Interleaving & ECC Reed-Solomon code (or convolutional code) BER pattern => interleaving

16 Coding Modulation codes For binary detection; balanced block code Interleaving & ECC Reed-Solomon code (or convolutional code) BER pattern => interleaving Equalization ISI (inter-symbol interference) effect suppression x x3(or 5x5) kernel Convolution Equalized data page x 0-5

17 Modulation code 0 :2 Modulation Code No modulation code a > b a b a < b 0

18 Detection Original image Method : Take the intensity of a sampling point (red point) of each block Method 2: Take the average of all intensities in each block

19 Array of code sequences Pages Code sequence Two dimensional array of decoders M.A Neifeld et al., Appl. Opt., 35, (995). Two dimensional array of code sequences [A][B][C][D] [E][F][G][H] [K][L][M][N] [Q][R][S][T] [A2][B2][C2][D2] [E2][F2][G2][H2] [K2][L2][M2][N2] [Q2][R2][S2][T2] [A3][B3][C3][D3] [E3][F3][G3][H3] [K3][L3][M3][N3] [Q3][R3][S3][T3] [AP][BP][CP][DP] [EP][FP][GP][HP] [KP][LP][MP][NP] [QP][RP][SP][TP] page page2 page3 pagep

20 Burst error correction Successful decoding is possible even if data pages are completely erased.

21 Page Recovery Without 0 pages 2, 0, 9, 23, 30, 36, 48, 49, 58, 68 (7,4) Hamming code

22 Example of burst error reference rotation damage detector lost page

23 Convolutional coding Convolutional codes Error correction codes Block codes BCH, RS Convolutional codes Soft decision decoding Extra coding gain Viterbi algorithm

24 Encoder (convolutional code) Encoder (n = 2, k =, m = 2) g = (7, 5) Modulo-2 adder Path Trellis diagram 00 0/ / / 0 /00 0 Input Flip-flop Output /0 0 0 /0 Path 2 0/0 0/0

25 Soft decision decoding in Viterbi algorithm Quantization of received signal into Q levels Q = infinite : ideal soft decision Q = 2 : hard decision Q = 8 : practically good enough 3 bits/sample A/D conversion of received signal makes 2dB extra coding gain at BER=0-5 compared to hard decision. Little increase of decoder complexity

26 Soft decision decoding Soft decision (Q=8) Discrete channel model Hard decision (Q=2) Binary channel model Likelihood of p(r s 0 ) Likelihood of p(r s ) Signal Hard decision data Sign-magnitude representation Most negative Least negative level soft decision Least positive level hard decision Most positive 0

27 Soft decision decoding Received symbol Received symbol Discrete channel model (Q=4) Conditional Probabilities Soft decision decoding for an (, 3) code Bit metrics Trellis Transmitted (,000,00,00,,00,,0) Received (0,00,00,0,0,0,,0) Decoded (,000,00,00,,00,,0)

28 Experiment Soft Decision Decoding Frequency Quantization level Q=2 Q=4 Q=8 Intensity [a.u.] BER 0.03~ ~ ~0.07 ON OFF Received symbol 0 Received symbol Interval 0 -INF INF 0.3 Q=2 Interval 0 -INF INF Q= Received symbol Interval 0 -INF INF 0.00 Q=

29 Intrapage intensity variations Best thresholds for 52 pages with 30x30 blocks (.3 inch diagonal SLM) Best thresholds for 70 pages with 50x50 blocks (0.24 inch diagonal SLM)

30 Sequence of Coding Generating pages RS (63,k) IBM mod(6:8) 2D square lattice Original data ECC encoding Modulation coding Interleaving Record/reconstruction Simulation : shift, Illumination, rotation, oversampling OR Experiment :LGE Retrieving data Alignment/F IR filtering Deinterleaving De-modulation ECC decoding Retrieved data

31 Examples Page generation condition Page size: 52x384 RS ECC: (63,5) Simulation condition Rotation: 0.2(rad) Shift: (0.2,0.3)(pixels) Illumination: 0.8: (of 0) Simulation (of 0) (of 0) (of 0)

32 시스템설계

33 Holographic Data Storage System (I) Ar Laser Controller Computer Shutter Beam Splitter Mirror Shutter 2 Iris Lens Beam Expander Iris Lens Mirror CCD Beam Expander SLM Motor Stage Photorefractive Material

34 HDS system (II) Beam splitter Beam expander :Reference beam CCD camera Beam expander :Signal beam Lens2 Iris: spatial filter Lens SLM Rotational stage

35 Exposure Schedule A t exp r τ = A0 r Recording time t r, M 3 t r, M 2 t r, M t r, M A = t Aexp e τ e t e, M t e, M 2 A = A t r ( t e 0 t r t e exp exp τ r τ e A te ) = τ r ln exp A0 τ e M t e = t, n t = t r, k k = n+ r, n r ( t e, n ) Recording time [sec] Hologram t e, M 3 t e, M 4

36 Diffraction efficiencies Intensity [a. u.] Hologram Intensity [a. u.] Hologram

37 SNR 6 5 SNR = m σ m 0 + σ SNR [db] Hologram m m 0 : mean of on-bit intensities : mean of off-bit intensities 2 σ : variance of on-bit intensities 2 σ 0 : variance of off-bit intensities

38 Image distortion detection () Zero distortion x M blocks x 3 N blocks Pincushion (or positive) distortion x 2 x 4 Barrel (or negative) distortion 2n + 2n + 2m+ [ x (2 ) + x2( )](2 ) 4 N N M 2n + 2n + 2m+ + [ x3(2 ) + x4( )]( ) 4 N N M

39 Image distortion detection (2) x x 2 x 3 x x x x 7 8 x x 9

40 Imaging System for Pixel-matching Imaging system Relay optics: data page scaling for detector (SLM pixel size: 36μm 36μm, CCD camera pixel size: 9μm 9μm ) => Aberration suppressed Reconstructed beam Group of lenses Fourier lens Cylindrical lens CCD camera CCD camera Group of lenses Lens Cylindrical Lens Designed imaging system Realized imaging system

41 HDS system HDS specification Angular multiplexing (extension possible with spatial multiplexing) Data page : /6Mbit Storage capacity : > 00 Mbit (/6Mbit x ~000 pages with extension) Data transfer rate : Mbit/s (/6Mbit x 6 frame/s) LabVIEW-based synchronization Beam splitter Beam expander :Reference beam CCD camera Realized HDS System Beam expander :Signal beam SLM Lens2 Iris: spatial filter Lens Rotational stage

42 Near-field Hologram Storage Object (fiber tip of the NSOM) Object wave (light from the fiber tip) Reference wave Photorefractive crystal Retrieved wave Photorefractive crystal Recording Retrieving

43 Field Components k 0 > k Air () Photorefractive crystal (n) k 0 < k <nk 0 nk 0 < k ~ / k

44 LG electronics Next-Generation Memory?

45 Milipede: A Complete Scanning-probe Storage System (IBM) LG electronics

46 Milipede: A Complete Scanning-probe Storage System (IBM) LG electronics

47 Milipede: A Complete Scanning-probe Storage System (IBM) LG electronics

A REDUCED COMPLEXITY TWO-DIMENSIONAL BCJR DETECTOR FOR HOLOGRAPHIC DATA STORAGE SYSTEMS WITH PIXEL MISALIGNMENT

A REDUCED COMPLEXITY TWO-DIMENSIONAL BCJR DETECTOR FOR HOLOGRAPHIC DATA STORAGE SYSTEMS WITH PIXEL MISALIGNMENT 1 S. Iman Mossavat, 2 J.W.M.Bergmans 1 iman@nus.edu.sg 1 National University of Singapore,