1. COEN 180 Optical Storage

2. Store data based on the optical properties of a device. Strong, established market for removable media. Small market for archival storage. WORM devices. Magneto-Optical Harder to erase data accidentally. Storage density limited by wavelength of light used. Shift from red to blue laser.

3. Optical Removable Storage Video Disk 1970s 1982 CD-DA (Phillips, Sony) 1985 CD-ROM (Phillips, Sony) 1995 DVD (Phillips, Sony, Toshiba, Time Warner)

4. CD-ROM CD-ROM: Standard Example for Optical Storage

5. CD-ROM... Spiral track (spiraling outwards) CD pit 0.5 * 2  m Dust 40  m Human Hair 70  m

6. CD-ROM... Disk Geometry 12 cm diameter 1.2 mm thick 1.5 cm center hole Spins at Constant linear velocity (CVL) Constant angular velocity (CAL) Areal density is 2Mb/mm 2

7. CD-ROM... 74 minutes of music 2 channels 44,100 samples/channel/second 2 B / sample 74 minutes 60 sec/minute = 783,216,000 B

8. CD-ROM... X-rating 1X = 150 KB/sec Up to 12X use CLV Adjust speed so that tracks are read at constant speed. After 12X use CAV Easier to build faster motors. Data rate now varies. X-rating is then an average.

9. CD-ROM... Focus laser beam on land area Sharp reflection from land. Dispersion from pit.

10. CD-ROM...

14. Mistracking detection: Main beam reads data, side beams tell whether there is a misregistration.

15. CD-ROM... Data encoding In principle, pits could be ones, lands zero, or vice versa. But long sequences are hard to detect. Use EFM modulation

16. CD-ROM EFM 8-14 modulation code words of length 14 bits that consists of single ones separated by two to nine zeroes 0000 1010  1001 0001 0000 00. The pits range in length from 3 bits to 11 bits. http://www.physics.udel.edu/~watson/scen1 03/efm.html

17. CD-ROM... Designation SizeByte Numbers Synchronization12B0-11 Header4B12-15 User Data2048B16-2063 Error Detection4B2064-2067 Space8B2068-2075 Error Correction276B2076-2351 Table 2: ECMA-130 Media Standard for Block Layout

18. CD Formats CD-AudioICE 908Red Book CD-ROMISO/IEC 10149Yellow Book CD-I Green Book Video CD White Book CD-recordableISO/IEC 11172/1/2/3Orange Book Logical Format CD-ROMISO-9660High Sierra CD-RecordableECMA 168 / IS 13940Frankfurt Proposal

19. CD-R CD-R disks have a layer of dye over the reflecting aluminium layer. The dye is photo- sensitive. In normal state, the dye is translucent, but after heating at a given frequency of light, the dye turns opaque, allowing us to store the data. A CD-R optical heat needs two laser light sources, to generate the write and the less intense read light. A CD-R disk has grooves pressed in to enable tracking with the read laser.

20. CD-RW

21. Can erase, i.e. undo the effect of a write. Use phase shift compounds Two phases of different reflectivity. Compound of Silver Antimony Tellurium Indium. Melts at 600 o C If it cools rapidly, it remains in a fluid, amorphous state that is quite opaque. If the cooling is slower, then the compound crystallizes into a quite translucent form at around 200 o C.

22. CD-RW The read layer in a CD-RW burner has not enough power to melt the compound. The higher power erase layer can heat the compound to the crystallization point and restore the original crystallization of the compound.

23. DVD Same basic technique as CD DVDs can use double layering Two reflective layers on a single surface. The inner one is made of aluminum (as for CD-ROM) The outer one is a semi-reflective gold layer through which the laser can focus on the inner layer. Maximum data capacity of 17GB, DVDs can be in a double sided, double layered format, where a total of four surfaces stores data.

24. DVD DVDs achieve higher data density per layer by halfing the dimensions of the pits / bumps on a CD: track pitch 740nm vs 1600 nm minimum pit length is 400 nm (440 nm on a double layer DVD) vs 830 nm. Since data is stored on a surface, this effectively quadruples the data density. Use of higher frequency light with a wave length of 640 nm as opposed to 780 nm for the laser used in CD-ROM.

25. DVD The error correction scheme on a DVD is much more sophisticated and powerfull than the one used for the CD- ROM standards, Progress in the theory of ECC Progress in the processing of data.