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:
Jan. 08, 1991
Filed:
Jul. 26, 1989
Shigeki Tsuji, Higashihiroshima, JP;
Taizo Yokota, Higashihiroshima, JP;
Sharp Kabushiki Kaisha, Osaka, JP;
Abstract
An optical head device for reading information stored in a recording medium wherein a light beam from a light source converges onto an optical disk and a beam reflected from the optical disk is received by a light receiving element to read information stored on the optical disk. This device includes a diffraction element having first diffraction gratings for dividing the light beam from the light source into a zero order diffracted beam utilized for reading the information stored on the optical disk and a pair of first order diffracted beams utilized for reading tracking errors. The diffraction element also has second diffraction gratings for guiding the beam reflected from the optical disk to a light receiving element. The transmission factors of the zero order diffracted beam of the first and/or second diffraction gratings in the regions located in the vicinity of both ends of the diffraction element are lower than those of the first and/or second diffraction gratings in the regions located in the vicinity of the center of the diffraction element. The ends and center are set in a direction corresponding to the radial direction of the optical disk.