LG Electronics GSA-4167B, GSA-4168B Disc structure, Recording principles, Data erased state

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 DVD+RW

Adhesive layer

Protective layer

Reflective layer

Dielectric layer

Recording layer

(Phase change material)

Dielectric layer Disc substrate

Adhesive layer

Protective layer

Reflective layer

Dielectric layer

Recording layer

(Phase change material)

Dielectric layer Disc substrate

> 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.

Substrate

Laser beam

Crystalline status Amorphous status

Recording data

(Melting/Quick cooling)

Erasing data

(Heating/Gradual cooling)

Data erased state	Recorded state
(High reflection coefficient)	(Low reflection coefficient)

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