1. Optical Data Storage By
Ken Tatebe

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 / mm2

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
Feature
DVD CD
Substrate Dia./Thick.
120 x 1.2 mm
Sides
1 or 2 1
Layers per side
Capacity (GB)
4.7, 8.54, 9.4, 17
0.7
Track Pitch (micron)
0.74
1.6
Min pit length (micron)
0.44
0.83
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/mm2

8. Dual Layer Technology Benefits Detriments 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 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.