Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
2001-05-25
2004-10-19
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S094000
Reexamination Certificate
active
06807142
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical information recording medium for recording and reproducing information with a large capacity using a laser beam and a method for initializing the same.
BACKGROUND ART
Examples of an optical information recording medium capable of recording and reproducing signals using a laser beam include a phase change type optical disk, a magneto-optical disk, and an optical disk using a dye material. In a recordable/erasable phase change type optical disk, a chalcogenide typically is used as a recording layer material. Generally, the crystalline state of the recording layer material is used as a non-recorded state. Signals are recorded by irradiating the recording layer material with a laser beam so as to melt and quench the recording layer material so that the material becomes amorphous. On the other hand, in order to erase signals, the recording layer is irradiated with a laser beam at a power lower than that for recording so that the recording layer becomes crystalline. Further, in order to reproduce recorded signals, the recording layer is irradiated with a laser beam at a power that does not cause the phase change of the material.
The recording layer made of a chalcogenide is formed in the amorphous state. Therefore, it is necessary to entirely crystallize a recording region beforehand to obtain a non-recorded state. Such entire crystallization of the recording region is called initialization. In general, the initialization process is incorporated in the disk production process and carried out using a laser beam source or a flash light source.
A recording medium with a so-called one-face-double layer structure has been proposed for the purpose of increasing the recording capacity of a recordable or a recordable/erasable phase change type optical disk. An optical disk with this one-face-double layer structure includes two information layers (multilayered films including recording layers) formed on a substrate. Signals are recorded or erased by a laser beam radiated through the substrate (i.e., radiated from the same direction).
In the phase change type optical disk with the one-face-double layer structure, when a first information layer on the side near the laser beam incident surface (i.e., the side near the substrate) is designed to have a “Hi to Lo structure” (H-L structure) in which a reflectance of the layer is decreased by recording (formation of an amorphous mark), and a second information layer distant from the laser beam incident surface (i.e., distant from the substrate) is designed to have a “Lo to Hi structure” (L-H structure) in which a reflectance of the layer is increased by recording (formation of an amorphous mark), the disk can serve as an optical information recording medium in which recording sensitivities of the first and second information layers and levels of the signals reproduced from these layers are uniform.
In the initialization process for the phase change type optical information recording medium with the one-face-double layer structure, what is important is whether stable focus control of the laser beam for initializing respective information layers is possible or not. However, in the medium including the first information layer with the H-L structure and the second a information layer with the L-H structure as described above, the second information layer presents a higher reflectance when the recording layer contained therein is amorphous than when it is crystalline, while the first information layer presents a lower reflectance when the recording layer contained therein is amorphous than when it is crystalline. Quantities of laser beams reflected from the first and second information layers are thus ill-balanced. Hence, when the recording layers in the recording region are entirely crystallized, it is difficult to obtain focus error signals from the first information layer while they are easily obtained from the second information layer.
With regard to initialization using a flash light source, the method conducted for a medium including a single information layer is already known (JP 62(1987)-250533 A). When the flash light source is used, the medium can be initialized in a shorter time period as compared with the case where a laser beam source is used.
However, in the optical information recording medium with a one-face-double layer structure, an attempt has never been made to initialize two information layers by a flash light radiated from the same direction. Unlike a laser beam, a focus of the flash light cannot be controlled. Furthermore, when the flash light is radiated from the substrate side for example, the second information layer has to be initialized by the light transmitted through the first information layer. In addition, different conditions should be adapted for initializing the first and second information layers because these layers generally have different structures in consideration of the fact that information signals are recorded/reproduced thereon/therefrom by the laser beam radiated from the same direction.
Therefore, in general, it is considered that the initialization using a laser beam is more appropriate for initializing the optical information recording medium with a one-face-double layer structure. However, initialization of the optical information recording medium with a one-face-double layer structure using the laser beam radiated from the same direction brings about some problems that do not occur in the case of the medium with a single layer structure.
DISCLOSURE OF INVENTION
An object of the present invention is to provide an initialization method suitable for an optical information recording medium with a one-face-double layer structure. It is another object of the present invention to provide a new optical information recording medium suitable for this initialization method.
In order to achieve the above-mentioned objects, the first optical information recording medium according to the present invention includes a substrate and at least a first information layer and a second information layer, and the first information layer and the second information layer, on/from which signals can be recorded/reproduced, are formed on the substrate in this order. The first optical information recording medium is characterized in that an area where the first information layer exists and the second information layer does not exist is provided on the substrate.
In the above-mentioned optical information recording medium, it is preferable that the substrate has a disk shape and the area where the first information layer exists and the second information layer does not exist is provided at least at one portion selected from an outermost circumference portion and an innermost circumference portion of an area where the first information layer exists. Furthermore, it is preferable that the first information layer includes a first recording layer and the second information layer includes a second recording layer, and the first and second recording layers are formed of a material that changes reversibly between an amorphous state and a crystalline state by irradiation of a laser beam from a side of the substrate.
In the above-mentioned optical information recording medium, with respect to a laser beam having a wavelength of &lgr;
0
radiated from the side of the substrate for reproducing signals recorded on the first and second recording layers, a reflectance R
0
(1amo) of the first information layer when the first recording layer is in an amorphous state, a reflectance R
0
(1cry) of the first information layer when the first recording layer is in a crystalline state, a reflectance R
0
(2amo) of the second information layer when the second recording layer is in an amorphous state, and a reflectance R
0
(2cry) of the second information layer when the second recording layer is in a crystalline state preferably satisfy the relationships:
R
0
(1amo)<
R
0
(1cry), and
R
0
(2amo)>
R
0
(2cry).
Further, in order to achieve the above-mentioned objects, the first method for initiali
Kawahara Katsumi
Nagata Ken'ichi
Nishiuchi Ken'ichi
Yamada Noboru
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Tran Thang V.
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