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:
Jun. 04, 2002
Filed:
Jul. 02, 2001
Hideki Hayashi, Nara, JP;
Tatsuo Ito, Osaka, JP;
Yoshiaki Komma, Hirakata, JP;
Hiroaki Yamamoto, Hyogo, JP;
Seiji Nishino, Osaka, JP;
Matsushita Electric Industrial Co., Ltd., Osaka, JP;
Abstract
In a photodetector, the minimum size of the photodetection area for detecting a focus error signal from a light beam on the inner radius side of a hologram is made smaller than the minimum diameter of diffracted light beam spots ( ) for recording and reproduction, and when a CD is reproduced, a light beam close to the optical axis is made to significantly contribute to the focus error signal and the minimum size of the photodetection area for detecting the focus error signal from a light beam from the peripheral side of the hologram is made larger than the minimum diameter of diffracted light beam spots ( ) for recording and reproduction, whereby the focus error signal is made equal to the normal focus error signal when a DVD is reproduced, so that the focus offset variation caused when the base material thickness varies can be reduced.