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:
Dec. 05, 2000
Filed:
Oct. 21, 1997
Tsutomu Matsui, Tokyo, JP;
NEC Corporation, Tokyo, JP;
Abstract
An optical disk apparatus of the present invention forms, in a first embodiment, two laser beams for erasure of data and irradiates the two laser beams from a single erasing head 102 so that focuses 207 and 208 thereof may be disposed on a same track of an optical disk 206. In order to construct the erasure head so as to provide two beams, either a two beam semiconductor laser 201 may be used or a beam from a semiconductor laser 215 may be divided into two beams. For the means for dividing the beam into two beams, a Wollaston polarizing prism 216, a Bragg diffraction grating 218, a Foucault prism 219 or some other suitable element can be used. Meanwhile, in a second embodiment, data are reproduced by an optical equivalence method using an optical disk 82, 100 or 206 of a phase change medium which exhibits a phase difference smaller than 180 degrees in reflected light therefrom based on recorded data. The phase difference preferably ranges from 120 degrees to 150 degrees. The phase difference can be made smaller than 180 degrees by adjusting the thickness of a protective film 12 on the light incidence side of the optical disk with respect to a phase change film 13.