Three Laser Beams From One Laser - Sony DVP S530D Training Manual

1.1 cm
C D F O C U S C O R R E C T E D

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.
Single
F o c u s
Point
Info Layer
C D
Objective
L e n s
D V D
Laser
Light
D V D
Laser
B e a m
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.
50
2 N D
1ST
Order
Order
1ST
2 N D
Order
Order
To
Objective
Lens
Defraction
Grading
Main
Laser
B e a m