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Optical Data Storage

Optical Data Storage. By Ken Tatebe 2004.11.1. 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. First Optical Storage Techniques.

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Optical Data Storage

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  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

  4. 20th 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/mm2

  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

  7. Road to the DVD • Innovations: • Dual layer • Increased numerical aperture • Decreased depth of focus • Signal to noise • Tracking • Data Density: ~7 MByte/mm2

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

  9. Numerical Aperture • NA = n sin(q/2) • Spot size = l/NA

  10. Depth of Focus • DoF = l/NA2 • 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 l down from 0.07 l

  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.

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