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. 01, 1999
Filed:
May. 16, 1995
Kenji Fukui, Sagamihara, JP;
Ricardo Musashi Okamoto, Yokohama, JP;
Pulstec Industrial Co., Ltd., Hamamatsu, JP;
Abstract
There is provided an optical pickup head which can accurately detect a focusing error even when the wavelength of light emitted from a light source varies. A holographic element diffracts a light beam reflected by an optical disk to obtain .+-.1st-order diffracted light beams, and has a diffracting area formed using a Fresnel zone plate, and a light-shading area for shading the reflected light beam. A photo-detector has four-elements light-receiving areas. The photo-detector detects the .+-.1st-order diffracted light beams diffracted by the diffracting area and focused by a convex lens, and converts these light beams into electrical signals. The photo-detector is disposed at substantially the middle point between the focal points of the -1st-order diffracted light beams formed by the convex lens. Since the middle point does not move even when the lasing wavelength of a semiconductor laser diode varies, the photo-detector can obtain stable signals.