Title: Apparatus for reading a record carrier with an optical information structure

Abstract: In an apparatus for reading a record carrier on which information is stored in an optically readable structure, the radiation which is supplied by the radiation source is split into a read beam and an auxiliary beam for determining the focussing of the read beam on the record carrier. Said auxiliary beam is intercepted by two radiation-sensitive detectors. By disposing a radiation-absorbing knife between the radiation source and the Wollaston prism a part of the auxiliary beam is blocked. Thus, an accurate indication can be obtained of the magnitude and the direction of a focussing error.

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Inventors: Boonstra, Lieuwe (Eindhoven, NL)
VAN Alem, Antonius A. M. (Eindhoven, NL)

Application Number: 812459
Filing Date: 1977-07-05
Publication_date: 1979-04-17
Assignee: U.S. Philips Corporation (New York, NY)
Primary Class(es): 369/44.24 369/44.37, 369/110.01, 369/112.19
Other Classes:
US Patent Ref:

T953002	Dec, 1976	Firester	179/100.
3829622	Aug, 1974	Elliot	179/100.
3876841	Apr, 1975	Kramer et al.	179/100.
3876842	Apr, 1975	Bouwhuis	179/100.
3969576	Jul, 1976	Boonstra et al.	179/100.

Other Refs:
Primary Examiner: Cardillo, Jr., Raymond F.
Assistant Examiner:
Attorney: Briody; Thomas A., Streeter; William J., Cohen; Simon L.