Optical scanning device for two types of record carriers
AssigneeKoninklijke Philips Electronics N.V.
InventorWillem G. Ophey
Life of this patent
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Abstract
In an optical scanning device suited for scanning two types of record carriers having a different thickness of their transparent layers and wherein an astigmatic element is used in combination with a quadrant detector for generating a focus error signal (Sf), this signal, which is generated when one type of record carrier is scanned, can considerably be improved by arranging an aspheric surface profile in only the central part of the beam coming from said one type of record carrier.
Claims6
An optical scanning device for scanning a first type of record carrier provided with a first information layer and a first transparent layer having a first thickness, and for scanning a second type of record carrier provided with a second information layer and a second transparent layer having a second thickness which differs from the first thickness, said scanning device comprising:
- a radiation source for supplying a scanning beam;
- an objective system for converging the scanning beam on the first information layer and on the second in formation layer;
- and
- a radiation-sensitive detector for converting the modulated scanning beam coming from the first and second information layers into electric signals, a radiation-sensitive surface of the detector having such an effective size that it receives radiation from a substantially complete scanning beam coming from the first type of record carrier and from substantially only the central part of a scanning beam coming from the second type of record carrier, characterized in that an aspherical surface having a size which is substantially equal to the cross-section of said central part is present in the path of only the modulated scanning beam between the objective system and the radiation-sensitive detector.
Dependencies are inferred from the claim text.