Single

1 . 1 cm

Focus

Point

Info Layer

C D

D V D

Laser

B e a m

Objective

Lens

D V D

Laser

Light

2 N D

1 S T

Order

Order

 

Main

 

Laser

 

B e a m

2 N D

1 S T

Order

Order

To

Objective

Lens

Defraction

Grading

CD FOCUS CORRECTED

Three Laser Beams from One Laser

Although there is one laser, there are three spots of light on the disc’s information layer. The three spots are made by diffraction grading inside the laser assembly.

A diffraction grading is made of a glass sheet with lines etched on it form- ing channels. The channels are represented by the spaces between the dotted lines in the diagram. As the main laser beam passes through a channel, secondary light beams are produced. The first order beams are the strongest and these are the two additional (side) spots that pass through the objective lens onto the disc. These side spots are used for CD track- ing.

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Image 55
Sony S530D manual Three Laser Beams from One Laser