Optikai adattárolás ma és holnap(után)

Átírás

1 Optikai adattárolás ma és holnap(után) Koppa Pál Technical University of Budapest Department of Atomic Physics

2 Tartalom I. A mai optikai adattárolók II. Az adatsűrűség III. Térfogati adattárolás IV. Holografikus adattárolás V. Optikai adattárolás a Műegyetemen VI. Fázisban modulált adatlapok VII. Mikroholografikus rendszer VIII. Konklúzió 2

3 I. Egy mai optikai adattároló felépítése 3

4 Mi van a lemezen? CD, DVD, BLU-Ray ROM: Pit & land interference CD, DVD, BLU-Ray R: Organic dye with permanent absorption change 4

5 Újraírható lemez CD, DVD, BLU-Ray +/ RW: Metal alloy with reversible phase change 5

6 A tárolási kapacitás fejlődése 6 Tegnap Ma Holnap És holnapután??? 650 MB 4.7 GB 25 GB

7 II. Az adatsűrűség NA nsin() Adatsűrűség: DD NA 0,6 2 nsin( ) 0,6 2 7

8 NA növelése? Elvileg lehetséges közeltéri (near-field) technikák: SIL (szilárd immerziós lencse) Elhaló hullám becsatolás (evanescent wave) csökkentése? UV lézer dióda elvileg lehetséges Diffrakciós limit áthágása??? Miért ne? Ld. superresolution 8

9 Írás túl a diffrakciós határon - egy példa Magneto-optical crescent recording Laser Beam Temperature Profile Small Crescent Domains Switching Threshold H H Media Motion 9

10 Olvasás Magnetic Super Resolution (MSR) Center Aperture Detection (CAD) Solves the Diffraction Limit Problem! However: Low signal levels Temp Profile Readout Layer Recording Layer Thermal Aperture In Plane Mask Side View Top View 10

11 A 2D adatsűrűség nagyságrendi növelése nem kézenfekvő! Megoldás??? Térfogati tárolás 11

12 3D adatsűrűség elvi határa: III. Térfogati tárolás Maximális adatsűrűség: ( Er) 2 max ( Er) 2 ( ) Er 2 DD Er) max ( 2 x,y NA 0,6 2 2 z NA NA 3 4 ~14 bit/mm 3 térfogati adatsűrűség (NA=0.85, l=400nm) ~ Gbit/inch 2 felületi adatsűrűség ~25 TB/lemez felhasználói kapacitás (R=125mm, t=1mm, CR=0.6) 12

13 CD térfogatosítása 2,4 rétegű Blu-ray lemez kapható 8, 16 réteg fejlesztés alatt ( GB) Abszorpció, transzmisszió, szórás SNR csökken Komplex és drága lemez-technológia 13

14 2 fotonos térfogati tárolás 14

15 Arany nanorudak, plazmonrezonancia 15

16 IV. Holografikus adattárolás 16

17 Multiplexelés Szög multiplexelés (síkhullám referencia) Fázis-kódolt multiplexelés (N síkhullám szuperpozíciója) 17 Hullámhossz multiplexelés (síkhullám referencia) Shift multiplexelés (gömbhullám referencia)

18 Holografikus tároló-anyagok Vastagság MUX száma r 2L sin( s) Dinamika tartomány Diffrakciós hatásfok M M # 2 Érzékenység Optikai minőség Zsugorodás, hőtágulás Írási sebesség Jel-zaj viszony Jel-zaj viszony Tipikus anyagok: fotorefraktív kristályok, fotopolimerek 18

19 InPhase Technologies Hologram felvétel 19

20 InPhase Technologies Hologram kiolvasás 20

21 Piacon kapható holografikus adattároló Drive 300GB capacity; 20MB/s, 160 Mb/s transfer rate WORM recording format 405 nm laser wavelength 21 Media 1.5 mm recording material 130 mm diameter disk 50 year archive life

22 Kollineáris rendszer Adatlap Optikai rendszer 22

23 servo system Mikroholografikus rendszer data control laser n detector multiplex collimator beam splitter Confocal filter beam splitter astigmatic lens quad objective lens actuator FES / TES reflector astigmatic lens actuator FES / TES quad Setup with confocal filtering 23

24 Az adatsűrűség fejlődése 24 Seagate HDD 2005 (421 Gb/inch 2 ) Samsung HDD 2011 (739 Gb/inch 2 ) microsdxc 2011 (2000 Gb/inch2) 8 rétegű Blu-ray 2007 (100 Gb/inch 2 ) Holographic (InPhase) 2006 (500 Gb/inch 2 )

25 V. Optikai adattárolás a Műegyetemen CD and MO technology ( in cooperation with VIDEOTON) Page oriented optical memory card ( with Optilink AB) Holographic data storage (from 1998 with Optilink and Bayer Innovations) 2 Photon volume optical data storage (1999 with EOARD, Univ. of Buffalo) Communication compatible all optical data storage (2001 with Deutsche Telecom) Technical support on CD/DVD RW manufacturing (from 2000 with Philips Hungary) High density holographic storage (ATHOS and MICROHOLAS from 2004) 25

26 Holographic Memory Card Demonstrator Systems Portable Holographic Storage Demonstrator Systems Read only and read&write units demonstrated Inherently secure data storage technology 2.77 bits/mm 2 (10 12 bit/cm 3 ) data density R/W unit power supply Read-only unit 26

27 Polarizációs holográfia Interference pattern (hologram) Reference beam Storage material Circular polarization Linear polarization Key features No -1 and higher diffracted orders High diffraction efficiency possible Requires photoanisotropic storage material 27

28 Read & Write System Optical Set-up Green laser source Beam expander Beam splitter Object SLM (transmissive) Mirror (aperture stop, Fourier filter) Fourier objective #1 Beam shaper Mirror λ/4 plate Fourier lens Reference beam Signal beam Read&Write head Beam contractor Mirror Aperture stop of reference arm Random-phase mask CCD array Polarisation filter λ/4 plate #2 Beam shaper Mirror 8f Fourier module Polarisation beam splitter Polarisation beam splitter with central hole in the splitting layer Fourier objective #2 Storage layer Memory card 28

29 Elements of the system 29

30 Reconstructed Data Page Constant weight sparse code modulation, 3x oversampling at CCD 16.4 Kbyte in a hologram, 2.77 bits/mm 2 (10 12 bits/cm 3 ) storage density raw symbol error rate: 10-4, user bit error rate after RS error correction:

31 Holographic Cryptography with phase coded reference wave Reconstruction Recording Input data FT of data Ref. wave FT π 0 π π 0 0 π 0 π π 0 0 Rec. wave π 0 π π 0 0 π 0 π π π π Correct code FT Output 0 0 π π 0 π π 0 π 0 0 π 0 π π 0 FT 31 π 0 0 π Different code

32 Reconstructed holograms Recording reference = Reconstructing reference Recording reference Reconstructing reference 32

33 Laser PBS Reference beam Object plane encoding Data encoding Amplitude SLM Phase SLM Aperture Phase mask SLM Hologram CCD Data recovery and ECC Object beam Reconstructed beam Does not make any encoding for amplitude images!!! Phase modulated data page is needed!! 33

34 Laser PBS VI. Fázisban modulált adatlapok Reference beam Phase SLM Data encoding Amplitude SLM Aperture Phase mask SLM Hologram CCD Data recovery and ECC Object beam Reconstructed beam Phase modulated data page: +Simple object arm +Smooth Fourier plane +Higher object power -Difficult data recovery 34

35 Phase to amplitude conversion Phase object electric field Phase object shifted Superimposed phase objects = Phase object intensity Shifted intensity Intensity of superimposed phase objects

36 Optical implementation E Circ. O Image duplication and shift by: Birefringent plate Diffraction grating Etc. BIS P45 CCD Opical axis =12 Clear aperture d25 mm d LTB (Li 2 B 4 O 7 ) Thickness t=6,2 mm 36

37 No. of occurences Log10(BER) Experimental results Simulation Experiment Experiment Simulation CCD Grey level (0..255) Fourier filtering [%] 37

38 Histogram spacing BER Tolerances Image phase SLM Shift (microns) Hologram misalignment (% of hologram size) 38

39 Encrypted storage /2 Obj Ref SLM 2 Reconstruction Recording SLM 1 FT lens Hologram FT lens SLM 3 BIS CCD 39

40 No. Of occurances Encrypted storage 500 Histogram CCD grey level (0..255) 40

41 No. Of occurances Object plane phase code Total histogram Logical 1-s Logical 0-s CCD grey level (0..255) 41

42 No. Of occurances Fourier plane phase code Total histogram Logical 1-s Logical 0-s CCD grey level (0..255) 42

43 No. Of occurances Dual phase code Total histogram Logical 1-s Logical 0-s CCD grey level (0..255) 43

44 servo system VII. Mikroholografikus rendszer data control laser n detector multiplex collimator Confocal filter beam splitter beam splitter astigmatic lens quad objective lens actuator FES / TES reflector astigmatic lens actuator FES / TES quad Setup with confocal filtering 44

45 The system model 1. Laser diode 2. Collimator lens 3. Objective lens + aperture 4. Disk 5. Microholograms in the disk 6. Confocal filter 1. Calculate scattering (4) diffracted field 2. Propagate to lens (3) far field wave 3. Add spherical phase (3) perfect lens 4. Cut wave by aperture (3) truncated Gauss 5. FFT of wave (2) beam focused on pinhole 6. Cut wave by pinhole (6) confocal filtering 45

46 46 Bragg diffraction calculations l l r r r r z z y y x x ik p d dxdydz z z y y x x e z y x n z z y y x x E k z y x z y x E ) ( ) ( ) ( ) ( ) ( ) ( ),, ( ),, ( 4 ),,,,, ( Volume scattering on weak index modulation Volume integral using the first Born approximation Both scalar and vector form can be integrated numerically Diffracted field Probe wave Index modulation Green function CC z y x E z y x E z y x n s r ),, ( ),, ( ),, ( ) ( ) ( 2 ) ( ) ( 2 ),, ( z i ikz z R y x ik z w y x e e z w E z y x E Linear material: Gaussian writing and reading beams:

47 Intensity distribution at output dz=0 dy=0 dz=6 mm dy=.5mm Confocal filter aperture size 47

48 First model results Index modulation of a microhologram Diffracted intensity at z=100 microns 48 Measurement FFT Born appr. Volume integral Longitudinal scan 532nm z [micrometer] Energy [a.u.] Transversal scan 532nm shift (micron) FFT Born approximation Measurement

49 Statistical evaluation Random hologram configurations 0.4mm Hologram pitch 50% white rate Track pitch: 0.7μm Hologram pitch : 0.4 μm Layer pitch : 6 μm Modeling up to 7 layers. Histograms of configurations mm Track pitch Reconstructed hologram Two nearest neighbors Holograms in the same layer Holograms in other layers

50 Bit error rate calculation W 0 (E) W 1 (E) BER E c 1 W 1 ( E) de W0 ( E) de N 0 Ec E c W 0 & W 1 : fitted probability distributions E c : read energy at crossing point N: No of bits in the histogram 50

51 Non-local saturation Exposure photo-polymerisation relaxation by monomer diffusion Sensitivity to next exposure proportional to monomer concentration Diffusion is to be taken into account! Calculation of polymer and monomer cc. as a function of time and space Result: non-linear, non-local material model Diffusion equation: u( x, t) t x u( x, t) D( x, t) x R( x, x') F( x', t) u( x', t) dx' Grad of mon. cc Diffusion constant Monomer concentration Light induced polymerization rate Change of monomer concentration Non-local material response 51 * J. R. Lawrence, F. T. O'Neill, J. T. Sheridan, Adjusted intensity nonlocal diffusion model of photopolymer grating formation, J. Opt. Soc. Am. B, Vol. 19, No. 4, Page , (April 2002)

52 Diffusion model results 52 If T exp T diff Saturation and possible fringe distortion Non-local response Provides the known CGS curve and M# If T exp << T diff and I exp << I sat Diffusion can be modeled with Gaussian smoothing of monomer concentration!

53 Holograms with non-local model Unequal diffraction efficiencies Non-local response Good fit to experimental scans 53

54 VIII. Konklúzió Holographic? 2 photon 3D? 5D?????? >1000GB (200 x DVD) Követelmények: -Nagy adatsűrűség, nagy adatátviteli sebesség -Hosszú archíválási idő -Biztonság -Könnyű kereshetőség -Olcsó adathordozó, nem nagyon drága meghajtó 54