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:
Jul. 12, 1988
Filed:
May. 16, 1985
Tsuneo Yanagida, Tokyo, JP;
Kiichi Kato, Tokyo, JP;
Olympus Optical Company Limited, Tokyo, JP;
Abstract
In a method of detecting track crossings on an optical disc, a light source irradiates a light beam onto an optical disc having guide tracks in the form of a recess and the light beam is reflected and diffracted into a zero order light beam and positive and negative primary light beams. The light beams are defocused so as to produce interference patterns between the zero light beam and the positive and negative primary light beams. The interference patterns are detected by a four split light detector disposed between two parts of a two split detector. The outputs of the detectors are fed to an adder and to a subtractor for producing a sum signal and a difference signal respectively. The sum signal and difference signal are fed to a phase detector. Defocusing of the light beams is effected by a focusing coil to which is fed the amplified output of an adder of a reference signal controlled by a control circuit.