Patent EP0253442A1 successfully refreshed from Google Patents.
EP0253442A1
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Apparatus for scanning an optical record carrier
Assignee: Koninklijke Philips NV
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Filing: 1987-07-08
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Granted: —
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Expires: 2007-07-08
Abstract
Abstract An apparatus for scanning an information surface (2) of an optical record carrier (1) is described. An error in the focussing of the scanning beam (b) on the information surface (2) is detected by means of two gratings (R₁, R₂) which are arranged one behind the other in the path of the beam ( b ) from the record carrier, which have grating periods (P) which are adapted to each other and whose grating strips intersect each other at a small angle (ϑ), use being made of a composite radiation-sensitive detection system (12).
Inventors
- 👤 Henricus Mathias Marie Kessels
- 👤 Christiaan Hendrik Frans Velzel
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-08 23:14
CPC Classifications
G; G11; G11B; G11B7/00; G11B7/08; G11B7/09; G11B7/0908; G11B7/0917
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
194 words
An apparatus for scanning an information surface of an optical record carrier, which apparatus comprises a radiation source, an objective system for focussing a radiation beam produced by the source so as to form a radiation spot on the information surface, and a focus-error detection system for determining a deviation between the plane of focusing of the objective system and the information surface, characterized in that the focus-error detection system comprises two diffraction gratings arranged one behind the other in the path of the beam from the record carrier, the grating period of the second grating being equal to that of the first grating mulitplied by a factor which is determined by the beam divergence, the planes of the grating extending parallel to each other and the grating strips of the second grating intersecting those of the first grating at a small angle, and in that there is provided a composite radiation-sensitive detection system and whereby the angle which the coordinate axes of this system make with the interference pattern formed at the location of this system depends on said deviation between the plane of focussing of the objective system and the information surface.
Claim 2
Independent Claim
194 words
An apparatus for scanning an information surface of an optical record carrier, which apparatus comprises a radiation source, an objective system for focussing a radiation beam produced by the source so as to form a radiation spot on the information surface, and a focus-error detection system for determining a deviation between the plane of focusing of the objective system and the information surface, characterized in that the focus-error detection system comprises two diffraction gratings arranged one behind the other in the path of the beam from the record carrier, the grating period of the second grating being equal to that of the first grating mulitplied by a factor which is determined by the beam divergence, the planes of the grating extending parallel to each other and the grating strips of the second grating intersecting those of the first grating at a small angle, and in that there is provided a composite radiation-sensitive detection system and whereby the angle which the coordinate axes of this system make with the interference pattern formed at the location of this system depends on said deviation between the plane of focussing of the objective system and the information surface.
Claim 3
Dependent Claim
23 words
An apparatus as claimed in Claim 1, characterized in that the second grating is arranged in a Talbot image of the first grating.
Claim 4
Dependent Claim
30 words
An apparatus as claimed in Claim 1 or 2, characterized in that only one band of the interference pattern is situated on the entire radiation-sensitive area of the detection system.
Claim 5
Dependent Claim
24 words
An apparatus as claimed in Claim 3, characterized in that one bright band of the interference pattern is situated on the radiation-sensitive detection system.
Claim 6
Dependent Claim
24 words
An apparatus as claimed in Claim 1, 2, 3 or 4, characterized in that the second grating is arranged against the radiation-sensitive detection system.
Claim 7
Dependent Claim
25 words
An apparatus as claimed in Claim 1, 2, 3 or 4, characterized in that the radiation-sensitive detection system is constructed as a grating-shaped detection system.
References Cited (Backward Citations)
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