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:
Mar. 04, 1997
Filed:
Nov. 07, 1994
Takeshi Yamazaki, Hachioji, JP;
Olympus Optical Co., Ltd., Tokyo, JP;
Abstract
An optical pick-up apparatus for reading and/or writing information from and/or on an optical record medium including a semiconductor laser, an objective lens projecting a laser beam onto the optical record medium, a hologram optical element having a first hologram for diffracting the laser beam onto a first pair of photodetectors to derive a focusing error and a second hologram for diffracting the laser beam onto a second pair of photodetectors to derive a tracking error. Each of the photodetectors of the second pair has light receiving regions which are divided along a division line substantially parallel with a diffracting direction of the second hologram which introduces astigmatism into the diffracted beams. A large tracking error signal can be detected stably on the basis of a distribution of an amount of light in a far field by the push-pull method.