Status and Trends of Optical Data Storage Technology

Transcription

1 Status and Trends of Optical Data Storage Technology Tom D. Milster University of Arizona Optical Sciences Center 1630 East University Blvd., Tucson, AZ, Phone: FAX: Presented at the THIC Meeting at the National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder CO August 21-22, 2007

2 Outline I. Introduction II. Today s Technology CD DVD BD, HD-DVD III. Trends that Influence Near-Term Development IV. Research and Development Volumetric (Holographic and Bit-Wise) Near-Field V. Conclusions 2

3 History The Inspiration and Invention SEM photo by Prof. G. Möllenstedt and R. Speidel. Inspiration for David Paul Gregg s invention of the Video Disk in 1958.* Lines in the green box are 30 nm wide and 90 nm apart. This performance not yet realized. spot size ~ 30 nm * see

4 Writing On a Spinning Disc (Single Layer) input data stream Encoder/ modulator Numerical aperture = NA = sin θ storage medium current drive signal newly written data θ laser source illumination optics intense light beam (half angle = θ) scan spot Input data stream is encoded into a drive signal for the laser Laser pulses energy through the illumination optics Light beam is focused to an intense laser spot Spot alters medium as disc rotates Introduction 4

5 Reading Data From a Spinning Disc (Single Layer) output data stream amplifier/ decoder current signal detectors storage medium servo/data optics reflected light data to be read θ laser source (low and constant power level) beam splitter illumination optics low-power light beam Low-power laser beam scans data pattern on spinning disc. Signal energy is directed with a beam splitter to detectors. Detectors produce a current signal, which is then decoded into user data. scan spot Introduction 5

6 Measures of Signal Quality detector curent I MAX Contrast (V) 20 log i 2 Narrow-band signal-to-noise ratio (SNR NB ) P S I MIN P N position frequency V = I MAX -I MIN I MAX + I MIN SNR NB = P S -P N In cases where media noise dominates (c = constant) SNR NB ~ log V - log c

7 Influence of Spot Size detector current marks along track spot x S I MAX,1 I MAX, 2 s I MIN,2 I MIN,1 x small s large s x S For closely spaced marks, spot size is the most important factor in determining contrast. Small spots yield good contrast. Small spots also allow the formation of smaller marks during the writing process. V 1 > V 2 V = I MAX -I MIN I MAX + I MIN

8 Numerical Aperture and Spot Size Light from Laser Marginal Ray Spot Profile Objective Lens Focused Spot Focused Beam Disc Surface θ m NA= sin θ m s μ m FW1/e 2 = s = λ/na Capacity 1/s 2 Decrease λ Increase NA

9 Evolution of Consumer Optical Storage HD-DVD 15 Gbyte Track Pitch: Minimum Pit Length: Storage Density: 9

10 Today s Optical Disc Media Technology clear side CD 1.2 mm center hole substrate* (clear) data layer DVD, HD-DVD 1.2 mm Blu-Ray, also called BD (without 1.2 mm cartridge) 0.6 mm 0.6 mm 0.1 mm clear side substrate* 1 (clear) data layer 1 (A,B) bonding agent data layer 2 (A,B) substrate* 2 (clear) clear side clear side protective layer (clear) data layer (A,B) substrate * Substrate also serves as protective layer Introduction 10

11 Trends that Influence Near-Term Development Historically unique applications for content distribution with CD media are being replaced with FLASH drives and internet distribution. Although the product cycle for CD has lasted much longer than originally expected, the CD is near the end of its (30+ year!) product cycle. DVD is now well accepted for distributing movie content and backup applications. BD and HD-DVD are being used for HDTV movie distribution. Titles are now available in Blockbuster stores. BD has the potential to be attractive for archive/professional application, due to its random access, longevity, and price competitiveness. (Price for BD-R is now below $0.40/GB, and significant price reductions are reasonable to expect in the next few years.) Due to the recent start of the BD product cycle, it is unlikely that new consumer products will be introduced with more advanced technology before Large optical data storage companies are now looking seriously at the enterprise/archive application that have been historically dominated by magnetic tape. 11

12 Optical Disc and Other Technologies 12

13 Research and Development Volumetric Holographic In-Phase Optware Bit-Wise Reflective Media Call/Recall Landauer Hitachi/Maxell SVOD Near-Field Solid Immersion Lens Super-Resolution media structure (SuperRENS) 13

14 Holographic Storage Data are stored in frequency space as three-dimensional gratings. 14

15 Holographic Storage Product Development 15

16 InPhase Recordable Technology Roadmap (From 2004 ODS Panel Discussion.) Current P P P P Specs 80 GB (80Gb/in2) 200 GB 20 MB/s 400 GB 40 MB/s 800 GB 80 MB/s 1600 Gb/in2 120 MB/s # of pages per book Reference Beam Sweep (degrees) Hologram pitch (θ, r) (mm) 1.0x , , , , 0.48 Nyquist filter / Beam Waist area 1.2x 1.2x 1.2x 1.2x 1.2x NA of object beam Bragg Null 3-4 th 2nd 2nd 2nd 1st SLM/Camera Pixels 1280x x x x x1280 Wavelength (nm) Angle and Polytopic Multiplexing Prototype of P1 October RW media and drive ~ 2007 see post deadline paper 16

17 Bit-Wise Volumetric Storage: The Vision Simple optical head for recording and reading L 1 L 2 L j L N Optical disc multi-layers using conventional thin-film media layers Disc motion N 100 s for 100 s times capacity of single disc. 17

18 Number of Layers Limit Due to Writing Threshold N (maximum number of layers) NA = 0.6 (405nm) NA = 1.2 (405nm) NA = 0.6 (638nm) NA = 1.2 (638nm) Unconstrained N τ = 1- R - A Assumptions: Limited total laser power: 100 mw Minimum irradiance required to write data: 5mW/μm 2 A = 0 No constraints on power used for readout Identical layers Maximum number of layers limited by transmission τ of each layer. 18

19 Effective Surface Density Due to Writing Threshold Π (Gb-in -2 ) NA = 0.6 (405nm) NA = 1.2 (405nm) NA = 0.6 (638nm) NA = 1.2 (638nm) Unconstrained PI τ = 1- R - A Assumptions: Limited total laser power: 100 mw Minimum irradiance required to write data: 5mW/μm 2 A = 0 No constraints on power used for readout. (Possible to approach writing threshold.) Identical layers Near-field system has significantly higher capacity. 19

20 Readout Limitation (with Absorption) N (maximum number of layers) NA = 0.6 (405nm) NA = 1.2 (405nm) NA = 0.6 (638nm) NA = 1.2 (638nm) Constrained N τ = 1- R - A Assumptions: Limited total laser power: 100 mw Minimum irradiance required to write data: 5mW/μm 2 A = 0.05 P DET = 0.1 mw N reduced to meet readout constraint at last layer so that I N <0.5I th Identical layers Large amounts of absorption (here 5%) can significantly reduce N for both constrained and unconstrained systems (by about the same factor). In addition, N suffers from a rollover effect at large τ in the constrained system when large absorption is present. 20

21 Readout Limitation (with Absorption) Π (Gb-in -2 ) NA = 0.6 (405nm) NA = 1.2 (405nm) NA = 0.6 (638nm) NA = 1.2 (638nm) Constrained PI τ = 1- R - A Assumptions: Limited total laser power: 100 mw Minimum irradiance required to write data: 5mW/μm 2 A = 0.05 P DET = 0.1 mw N reduced to meet readout constraint at last layer so that I N <0.5I th Identical layers Π is also reduced in a similar manner, due to the reduction in N. 21

22 Two-Photon Nonlinear Media Absorption (Many Layers) linear media nonlinear media layer of interest absorbed light separation between data layers absorbed light focus cone z z Nonlinear absorption characteristics can be used effectively with volumetric memories to isolate a layer of interest. 22

23 Call/Recall 2-Photon Volumetric 2-Photon storage 1 diameter disk holds 500 GB with 500 Mbit/sec minimum parallel readout speed. (Figure courtesy Call/Recall, Inc.) 23

24 Call/Recall 253GB Demo ODS

25 Landauer AlOx Volumetric Media (ODS 2007) Sapphire substrate stable to 600C Uses low-power lasers for writing 25

26 Hitachi/Maxell Stacked Volumetric Optical Disc (SVOD) 1TB cartridge 100 disks per cartridge DVD density 92μm thick substrates Price ~$0.10/GB (???) 26

27 Near-Field ODS: Solid Immersion Lens (SIL) marginal ray objective lens light from laser sin θ m = sin θ λ= λ n SIL m (Light waves slow down, but oscillation frequency remains the same.) θ m t=r t data r θ m s n SIL Spot size reduced by n SIL. λ λ/ n λ λ s s = = = = = sin θ sin θ n NA NA n m m SIL air SIL Small spot size High efficiency Capacity increase by n SIL2. S. M. Mansfield and G. S. Kino, Solid immersion microscope, Appl. Phys. Lett., 57(24) 2615 (1990) 27

28 SIL Performance 1/e 2 Spot Size (nm) LaSF35, NA EFF = 1.45 (C.A. Verschuren et al.) S-LAH79, NA EFF = 1.84 (M. Shinoda et al.) LaSF35, NA EFF = 1.9 (C.A. Verschuren et al.) Bi 4 Ge 3 O 12, NA EFF = 2.05 (M. Shinoda et al.) GaP, NA EFF = 2.2 (M. Lang et al.) KTaO 3, NA EFF = 2.2 (M. Shinoda et al.) Diamond, NA EFF = 2.38 (M. Shinoda et al.) Maximum Capacity/layer (GB) Refractive Index Wavelength=405nm, disk 1 st surface NFR optics Wavelength=530nm, disk 1st surface NFR optics Wavelength=405nm, cover-layer incident NFR optics SOURCE: INSIC Roadmap 28

29 SIL Multi-Layer Technology Two-layer Philips NF system Thin cover layer and spacer High index materials 60-80GB per layer demonstrated 200 GB/layer possible SOURCE: JJAP, vol 46, no. 6B, 2007, p

30 Super-RENS Media Near-field interaction using media layers. Conventional DVD and BD recording and readout optics with advanced electronics. SOURCE: INSIC Roadmap 30

31 Super-RENS Media 37.5 nm (100 GB) mark shape: (a) track direction TEM image, (b) radial direction TEM image, and (c) 3-dimensional image of 37.5 nm recorded marks. (SOURCE: INSIC Roadmap) 31

32 Conclusions Optical disc technology is currently providing products for content distribution and archiving. As the CD product cycle declines, DVD and BD/HD-DVD products ramp up. Advanced technologies, like volumetric and near field, probably won t be introduced into consumer products for several years. Initially, these technologies can provide 200GB-500GB/disc. A likely target for the advanced technologies is the professional/enterprise market. The potential for ODS is well beyond 1TB/disk, and it has the potential to be price competitive with tape. 32