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. 25, 1997
Filed:
Dec. 15, 1994
Applicant:
Inventors:
Kimio Tatsuno, Tokyo, JP;
Takeshi Shimano, Hachioji, JP;
Hiroshi Fukuda, Kodaira, JP;
Osamu Komoda, Kokubunji, JP;
Assignee:
Hitachi, Ltd., Tokyo, JP;
Attorney:
Primary Examiner:
Int. Cl.
CPC ...
G11B / ;
U.S. Cl.
CPC ...
369112 ; 369103 ; 369100 ; 372 32 ; 372103 ;
Abstract
An optical head apparatus for recording and reproducing data to and from optical disks, the apparatus boosting recording density by use of an objective lens with a higher numerical aperture (NA) than ever. A phase plate is added to the pupil position of the objective lens or to a position close thereto. The phase plate arrangement provides a deeper focal length, reduces the adverse effects of aberration and eliminates the need for a tilt servo mechanism despite the use of the objective lens having a greater numerical aperture than before.