Elektroonika Alused
The emerging light (now polarized parallel to the page) is then collimated.
The collimated light goes through a 1/4 wave plate. This converts it into circularly polarized light.
The circularly polarized light is then focused down onto the disk. If the light strikes "land" it is reflected back
into the objective lens. (If the light strikes the pit, now a bump, it is not reflected.)
The light then passes through the 1/4 wave plate again. Since it is going the reverse direction, it will be polariz
perpendicular to the original beam (in other words, the light polarization is now vertical with respect to the
paper).
When the vertically polarized light hits the polarizing beam splitter this time, it will be reflected (not transmitt
as before). Thus, it will reflect though the focusing lens and then the cylindrical lens and be imaged on the
photodetector array. The cylindrical lens is important in the auto-focusing mechanism.
E. Three beam autofocus
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