LG GSA-4167B Service Manual page 26

3) Recording format using phase-change recording material (DVD-RW/DVD+RW)
* Data is recorded by changing the recording layer from the amorphous status to the crystalline status, and
played back by reading the difference of the reflection coefficient.
[ Amorphous : Non-crystalline ]
> Disc structure
DVD-RW
> Recording principles
[Recording]
When a high-power laser is applied to the recording material, it melts and then becomes amorphous with
a low reflection coefficient when it quickly cools off. When a mid-power laser is applied to heat gradually
the recording material and then gradually cools it off, it becomes crystal with a high reflection coefficient.
[Playback]
A low-power laser is used for playback. The amount of reflected light depends on the status (amorphous
or crystalline) of the recording material. This is detected by an optical sensor.
Crystalline status
Data erased state
(High reflection coefficient)
DVD+RW
Adhesive layer
Protective layer
Reflective layer
Dielectric layer
Recording layer
(Phase change material)
Dielectric layer
Disc substrate
Substrate
Recording data
(Melting/Quick cooling)
Erasing data
(Heating/Gradual cooling)
(Low reflection coefficient)
Adhesive layer
Protective layer
Reflective layer
Dielectric layer
Recording layer
(Phase change material)
Dielectric layer
Disc substrate
Laser beam
Amorphous status
Recorded state
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