Focussing system and methods for multi- track optical disk appar

Details Focussing system and methods for multi- track optical disk appar Focussing system and methods for multi- track optical disk appar

1997-04-25

1998-06-30

Young, W. R.

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369112, G11B 7095

Patent

active

057744327

ABSTRACT:
Focussing system methods and apparatus are provided for apparatus capable of simultaneously reading multiple tracks of an optical disk. Astigmatism introduced by a cylindrical lens disposed adjacent to the light source, or before the focus detectors arranged at the edge of a wide-area field of illumination, is used to compute an error signal corresponding to the degree of out-of-focus, which error signal is provided to a servo-system that moves the objective lens to correct the focus. An alternative embodiment employs a pair of focus detectors and a pair of micro-lenses having different focal lengths that directs the reflected light onto the focus detectors to generate a focus correction signal. Further alternative embodiments of employing the astigmatism method of focussing are described.

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