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. 31, 2012
Filed:
Sep. 14, 2009
Noriyuki Kawano, Tokyo, JP;
Tetsuya Nishiyama, Tokyo, JP;
Yoshinori Sato, Tokyo, JP;
Koji Mishima, Tokyo, JP;
Hajime Utsunomiya, Tokyo, JP;
Noriyuki Kawano, Tokyo, JP;
Tetsuya Nishiyama, Tokyo, JP;
Yoshinori Sato, Tokyo, JP;
Koji Mishima, Tokyo, JP;
Hajime Utsunomiya, Tokyo, JP;
TDK Corporation, Tokyo, JP;
Abstract
An optical head device (optical head) for a multi-layered optical recording medium has a focus control mechanism that makes use of astigmatism. The focus control mechanism has a sensor lens that includes a cylindrical lens. The focus control mechanism causes a light beam having passed through the sensor lens to have astigmatism, thereby being focused linearly in the Y direction on a front focal line located closer to the sensor lens and focused linearly in the X direction at a rear focal line located farther therefrom. The optical head also includes a photodetector which is disposed between the front focal line and the rear focal line to detect a focal position from the shape of a light beam. At the position of the front focal line, a shield plate with a window portion is disposed. The window portion has a size so as to allow the focal line to pass therethrough and shield stray light reflected from an unfocused recording layer.