Writable and Rewritable CD’s By Thomas Szychowski.
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Transcript of Writable and Rewritable CD’s By Thomas Szychowski.
Writable and Rewritable CD’s
By
Thomas Szychowski
The CD
Written from inside out TOC is written first Last two mm left open Three types
– Pressed– CD-R– CD-RW
Pressed CD
Data is pressed on an aluminum layer
Physical Pits and Lands
Data is seen through the transition from one depth to another
Differences from Pressed and “burned” CDs
Pressed– Metallic layer with different heights
Burned– Everything is generally at the same height– Reflection is manipulated using lasers to create
differences– Compounds are dyes that are responsive to
localized heat
CD-R
CD – Recordable Data kept on an organic dye compound
– Normally reflective
Laser “burns” areas in the die to represent a bump– Heats the dye to a critical point to change the materials
properties– Burned areas are far less reflective than non-burned ones
Permanent and irreversible
CD-RW
CD – Rewritable Phase changing data layer Data is kept on a special combination of antimony, indium, silver and tellurium
– Reflective originally Three laser powers
– Read power Lowest power setting
– Erase power More powerful than Read-power Sets the compound from Dull back to original state when cooled
– Write power most powerful Creates a non-reflected area
– Heated area is non-crystalline when cooled
Laser Power – CD-R
cyanine dye – 6.5 mW at burn-speed of 1x– Faster burn speed means more powerful laser.
Phthalocyanine– Alternative to cyanine dye– Excellent longevity– Lower powered laser at 1x – 5.5mW
Laser Power – CD-RW
Power levels– Read State
Low power– Low enough to not affect the chemical compound
– Erase State Medium power
– Temperature is below the melting point, but above the crystalline temp (~200ºC)
– Atoms revert to crystalline form– Write State
Highest power– Temperature rises to 500ºC to 700ºC – creates an amorphous state
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