US4460990A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Apparatus for reading an optical record carrier
Assignee: US Philips Corp
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Filing: 1982-01-18
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Granted: 1984-07-17
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Expires: 2002-01-18
Abstract
Abstract An apparatus is described for reading an optical information structure arranged in tracks. By the use of a substantially rotationally symmetrical element having an annular radiation-attenuating peripheral portion cross-talk between the tracks as a result of obliquity of the information structure is substantially reduced.
Inventors
- 👤 Willem G. Opheij
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 12:07
CPC Classifications
G; G11; G11B; G11B7/00; G11B7/12; G11B7/135; G11B7/1392; G11B7/13922; G11B7/1381
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
211 words
An apparatus for reading information from a record carrier having an information structure comprising a plurality of generally parallel information tracks, said apparatus comprising means for producing a beam of radiation, an optical system for projecting said beam onto said record carrier, said optical system including means for focusing said beam to a circular spot on an information track to be read so as to modulate the radiation of said beam in accordance with information stored in said track, and a radiation-sensitive detector disposed in the path of the modulated radiation, said optical system further including a substantially rotationally symmetrical radiation attenuating element arranged in the radiation path at a location which is traversed only by radiation which is traveling towards said record carrier, said attenuating element comprising a central portion and an annular peripheral portion such that there is an abrupt transition between said central and peripheral portions, said central portion transmitting the central portion of said beam substantially unattenuated and said peripheral portion providing substantial attenuation of the amplitude of the peripheral portion of said beam so as to reduce cross-talk due to assymmetry in the intensity distribution of the radiation incident on said information structure when said beam is not perpendicular to the surface of said record carrier.
Claim 2
Independent Claim
211 words
An apparatus for reading information from a record carrier having an information structure comprising a plurality of generally parallel information tracks, said apparatus comprising means for producing a beam of radiation, an optical system for projecting said beam onto said record carrier, said optical system including means for focusing said beam to a circular spot on an information track to be read so as to modulate the radiation of said beam in accordance with information stored in said track, and a radiation-sensitive detector disposed in the path of the modulated radiation, said optical system further including a substantially rotationally symmetrical radiation attenuating element arranged in the radiation path at a location which is traversed only by radiation which is traveling towards said record carrier, said attenuating element comprising a central portion and an annular peripheral portion such that there is an abrupt transition between said central and peripheral portions, said central portion transmitting the central portion of said beam substantially unattenuated and said peripheral portion providing substantial attenuation of the amplitude of the peripheral portion of said beam so as to reduce cross-talk due to assymmetry in the intensity distribution of the radiation incident on said information structure when said beam is not perpendicular to the surface of said record carrier.
Claim 3
Dependent Claim
31 words
An apparatus as claimed in claim 1, wherein the peripheral portion of the radiation-attenuating element is formed by a layer which is vacuum-deposited on an optical element of said optical system.
Claim 4
Dependent Claim
27 words
An apparatus as claimed in claim 1, wherein the thickness of the vacuum-deposited layer is some orders of magnitude smaller than the wavelength of the radiation beam.
Claim 5
Dependent Claim
46 words
An apparatus as claimed in claim 1, 2 or 3, wherein the diameter of the central portion of the radiation-attenuating element is substantially half that of said element and the amplitude attenuation of the peripheral portion is within the range of approximately 40% to approximately 50%.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1987-07-17 | 1988-01-16 | 1988-07-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-07-17 | 1992-01-16 | 1992-07-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-07-17 | 1996-01-16 | 1996-07-17 | $7700.00 | Window Closed / Lapsed |