1. Optical Data Storage By Ken Tatebe 2004.11.1

2. Outline  Basic Technology  CD: Properties and Capabilities  DVD: Comparison to CD  What’s makes DVD’s better?  Comparison to other contemporary data storage technologies  Future directions

3. First Optical Storage Techniques  Writing systems represent the first optically based data storage methods, replacing oral records.  Storage Capacity: ~ 0.01 byte / mm 2 ~ 0.01 byte / mm 2

4. 20 th Century: The Compact Disc  Patented in 1970 by James T. Russell as a means for durable audio data storage.  First digital optical data storage; inspired by punch cards and magnetic storage devices.  Mass production starts in 1985 by Philips and Sony.  Gives practical use to Reed – Solomon Error Correction.  Data Density: ~ 1Mbyte/mm 2

5. Tracking and Error Correction  Diagonally astigmatic lens coupled with quadrant photocell.  Difficult to keep focus stable across all freq.  1 mm surface spot size due to high NA  Reed - Solomon correction codes  Over-sampled polynomial using data as coefficients

6. DVD: Improvements to CD FeatureDVDCD Substrate Dia./Thick. 120 x 1.2 mm Sides 1 or 2 1 Layers per side 1 or 2 1 Capacity (GB) 4.7, 8.54, 9.4, 17 0.7 Track Pitch (micron) 0.741.6 Min pit length (micron) 0.440.83 Linear scan velocity 3.6 m/s 1.3 m/s Laser wavelength 635 nm 780 nm Numerical Aperture.6.45 Modulation 8 to 16 8 to 17 Spot Size 1058 nm 1733 nm

7. Road to the DVD  Innovations:  Dual layer  Increased numerical aperture  Decreased depth of focus  Signal to noise  Tracking  Data Density: ~7 MByte/mm 2

8. Dual Layer Technology  Benefits  Increased durability  Increased capacity  Detriments  Decreased S/N  Decreased data density

9. Numerical Aperture  NA = n sin(  /2)  Spot size = /NA

10. Depth of Focus  DoF = /NA 2  Determines spacing of layers  Affects S/N; places an upper limit on NA.

11. Noise Tolerances  Coma Aberrations  Laser more stable at -135 db/Hz  Eccentricity 100 micron down from 140 micron  Surface aberration of 0.033  down from 0.07  Surface aberration of 0.033  down from 0.07

12. Hard drives

13. Future Data Disc Advances

14. Non-linear Upgrades  2 – Photon absorption to decrease depth of field for more layers  Magnetic Super-Resolution: 100 nm spot size.  Separate layers by narrow spectral response.  Shorter wavelength (freq. doubled?)

15. Volumetric Storage  “K – Vector” Addressing: a.k.a. Holographic addressing  2 beam intersection: issues with reaching diffraction limits  Interferometer based path length addressing

16. References  Optical Data Storage. Coufal, Hans, Geoffrey Burr: International Trends in Optics, 2002.  DVD Focus Control. Lincoln, Bo: Lecture notes.  Smith, Steven W. The Scientist and Engineer’s Guide to Digital Signal Processing. San Diego: California Technical Publishing, 1997.  Usbyte.com  Pioneer.co.jp  Optical-disk.com  Hecht, Eugene. Optics. Reading: Addison Wesley Longman, 1998.  Magnetic Super Resolution: Fujitsu.