The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Apr. 14, 1992
Filed:
Aug. 08, 1990
Zahirudeen Premji, Boulder, CO (US);
Nikon Corporation, Tokyo, JP;
Abstract
An objective lens having chromatic aberration is disposed in an optical system for focusing recording and/or reproducing light beams upon a surface of an optical disc, and two detecting light beams having different wavelengths are passed through the lens. When the surface of the optical disc is positioned at a focal point of one of the beams, the other beam is not focused on the optical disc. When the surface of the disc is positioned midway between the focal points of the two beams, two light spots formed on the optical disc by the two beams have equal intensity. The light intensity of the two spots is detected, so that focusing errors can be determined based on the difference between the detected intensities.