Optikai adattárolás ma és holnap(után) Koppa Pál Technical University of Budapest Department of Atomic Physics www.fat.bme.hu
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
I. Egy mai optikai adattároló felépítése 3
Mi van a lemezen? CD, DVD, BLU-Ray ROM: Pit & land interference CD, DVD, BLU-Ray R: Organic dye with permanent absorption change 4
Újraírható lemez CD, DVD, BLU-Ray +/ RW: Metal alloy with reversible phase change 5
A tárolási kapacitás fejlődése 6 Tegnap Ma Holnap És holnapután??? 650 MB 4.7 GB 25 GB
II. Az adatsűrűség NA nsin() Adatsűrűség: DD NA 0,6 2 nsin( ) 0,6 2 7
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
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
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
A 2D adatsűrűség nagyságrendi növelése nem kézenfekvő! Megoldás??? Térfogati tárolás 11
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 2 5.5 NA 3 4 ~14 bit/mm 3 térfogati adatsűrűség (NA=0.85, l=400nm) ~12 000 Gbit/inch 2 felületi adatsűrűség ~25 TB/lemez felhasználói kapacitás (R=125mm, t=1mm, CR=0.6) 12
CD térfogatosítása 2,4 rétegű Blu-ray lemez kapható 8, 16 réteg fejlesztés alatt (200-400 GB) Abszorpció, transzmisszió, szórás SNR csökken Komplex és drága lemez-technológia 13
2 fotonos térfogati tárolás 14
Arany nanorudak, plazmonrezonancia 15
IV. Holografikus adattárolás 16
Multiplexelés Szög multiplexelés (síkhullám referencia) Fázis-kódolt multiplexelés (N síkhullám szuperpozíciója) 17 Hullámhossz multiplexelés (síkhullám referencia) Shift multiplexelés (gömbhullám referencia)
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
InPhase Technologies Hologram felvétel 19
InPhase Technologies Hologram kiolvasás 20
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
Kollineáris rendszer Adatlap Optikai rendszer 22
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
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 )
V. Optikai adattárolás a Műegyetemen CD and MO technology (1988-91 in cooperation with VIDEOTON) Page oriented optical memory card (1995 98 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
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
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
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
Elements of the system 29
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: 10-12 30
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 0 0 0 0 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
Reconstructed holograms Recording reference = Reconstructing reference Recording reference Reconstructing reference 32
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
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
Phase to amplitude conversion Phase object electric field Phase object shifted Superimposed phase objects 1-1 1-1 -1 1-1 1 0 0 0 0 0 0 0 0 1-1 1-1 -1 1-1 1 0-1 1-1 1 1-1 1-1 0 1-1 1-1 -1 1-1 1-1 2-2 2 0-2 2-2 1-1 1 1 1-1 -1-1 1 0-1 1-1 1 1-1 1-1 -1 0 2 0 0 0-2 2-1 1-1 1-1 1 1 1-1 0-1 1 1 1-1 -1-1 1 1-2 2 0 2 0 0-2 1-1 -1 1 1-1 -1-1 -1 + 0 1-1 1-1 1-1 1-1 = -1 0 0 2-2 0-2 0-1 1-1 -1 1 1 1 1-1 0-1 -1 1 1-1 1-1 -1 1-2 -2 2 2 0 2-2 -1-1 1 1 1-1 -1-1 1 0 1-1 -1 1-1 1 1-1 -1 2 0 0 0-2 0 2-1 -1 1 1-1 1-1 1-1 0-1 1 1 1-1 -1-1 1-1 0 2 0 2-2 0-2 1-1 1 1-1 1-1 1-1 0-1 1 1-1 1-1 1-1 Phase object intensity Shifted intensity Intensity of superimposed phase objects 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 4 4 4 0 4 4 4 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 0 4 0 0 0 4 4 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 4 4 0 4 0 0 4 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 0 0 4 4 0 4 0 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 4 4 4 4 0 4 4 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 4 0 0 0 4 0 4 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 0 4 0 4 4 0 4 1 0 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 35
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
No. of occurences Log10(BER) Experimental results Simulation Experiment 3000 2500 2000 0-2 -4 Experiment Simulation 1500 1000 500 0 0 25 50 75 100 125 150 175 200 CCD Grey level (0..255) -6-8 -10-12 0 25 50 75 100 125 150 Fourier filtering [%] 37
Histogram spacing BER Tolerances 1 0 5 10 15 20 25 0.1 0.01 0.001 0.0001 Image phase SLM Shift (microns) 120 100 80 60 40 20 0 3 4 5 6 7 8 9 10 11-20 -40-60 Hologram misalignment (% of hologram size) 38
Encrypted storage /2 Obj Ref SLM 2 Reconstruction Recording SLM 1 FT lens Hologram FT lens SLM 3 BIS CCD 39
No. Of occurances Encrypted storage 500 Histogram 400 300 200 100 0 0 50 100 150 200 250 300 CCD grey level (0..255) 40
No. Of occurances Object plane phase code 500 400 300 Total histogram Logical 1-s Logical 0-s 200 100 0 0 50 100 150 200 250 300 CCD grey level (0..255) 41
No. Of occurances Fourier plane phase code 500 400 300 Total histogram Logical 1-s Logical 0-s 200 100 0 0 50 100 150 200 250 300 CCD grey level (0..255) 42
No. Of occurances Dual phase code 500 400 300 Total histogram Logical 1-s Logical 0-s 200 100 0 0 50 100 150 200 250 300 CCD grey level (0..255) 43
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
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 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 2 1 2 1 2 1 ) ( ) ( ) ( 2 1 1 1 ) ( ) ( ) ( ),, ( ),, ( 4 ),,,,, ( 2 1 2 1 2 1 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 ) ( 0 2 2 2 2 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:
Intensity distribution at output dz=0 dy=0 dz=6 mm dy=.5mm Confocal filter aperture size 47
First model results Index modulation of a microhologram Diffracted intensity at z=100 microns 48 Measurement FFT Born appr. Volume integral Longitudinal scan 532nm 0-15 -10-5 0 5 10 15 z [micrometer] 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 Energy [a.u.] 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Transversal scan 532nm -3-2 -1 0 1 2 3 shift (micron) FFT Born approximation Measurement
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 10 000 configurations 49 0.7mm Track pitch Reconstructed hologram Two nearest neighbors Holograms in the same layer Holograms in other layers
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
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 621-629, (April 2002)
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!
Holograms with non-local model Unequal diffraction efficiencies Non-local response Good fit to experimental scans 53
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