Method for erasing rewritable optical disk using two laser beams

Details Method for erasing rewritable optical disk using two laser beams Method for erasing rewritable optical disk using two laser beams

1995-11-15

1997-04-15

Dinh, Tan

Dynamic information storage or retrieval

Simultaneous diverse types of storage or retrieval

3692755, G11B 1300

Patent

active

056217072

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.

REFERENCES:
patent: 4972396 (1990-11-01), Rafner
patent: 4998238 (1991-03-01), Mizunoe et al.
patent: 5276674 (1994-01-01), Tanaka
patent: 5333124 (1994-07-01), Kikuchi et al.
"Mark Edge Recording Characteristics on Phase Change Optical Disks", by M. Okada et al., Technical Report of IEICE, MR 93-53, CPM93-105, Dec. 1993.

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