Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
1999-05-14
2002-09-24
Young, W. R. (Department: 2653)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S283000, C369S094000
Reexamination Certificate
active
06456584
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical information recording medium, especially an optical disk, for recording and reproducing a large capacity of information with a laser beam, and recording and reproduction therefor.
2. Description of Prior Art
A read-only optical recording medium with a laser beam includes optical disks called as a compact disk (CD), a laser disk (LD) and a digital video disk (DVD). Among the commercial read-only optical information recording media, a DVD disk can record signals at the highest density. According to the DVD format, a read-only DVD has diameter of 120 mm, and a user capacity of 4.7 GB at maximum for single layer type for single side reading, that of 9.4 GB for single layer type for double side reading, or that of 8.5 GB for two-layers type for single side reading. For example, a two-layers type DVD for single side reading has first and second information layers, and signals recorded in either of first and second information layers can be reproduced with a laser beam irradiated from one side of the optical disk. A method for fabricating a read-only DVD having a multi-layer structure is described for example in U.S. Pat. No. 5,126,996.
Optical information recording media which can record and reproduce signals with a laser beam include a phase-change type optical disk, a magneto-optical disk and a dye disk. In a phase-change type optical disk, a chalcogenide is used usually as a recording thin film material. Generally, when the recording thin film material is in the crystalline state, it is taken as a non-recorded state. A signal is recorded by irradiating a laser beam to melt the magnetic thin film material and to cool it quickly to the amorphous state. When a recorded signal is erased, a laser beam having a power lower than that for recording is irradiated to change the recording layer to the crystalline state. Because the chalcogenide magnetic thin film is formed with deposition in the amorphous state, it is necessary to crystallize all the surface of the recording region beforehand to result in the non-recorded state. This initial crystallization is usually included in a part of the disk manufacturing steps. A recording thin film is crystallized with a light source of a laser light source or a flash one.
In order to enhance the signal recording speed for a phase-change type optical disk on which recording and erasing are possible, so-called light absorption correction is proposed which is suitable for high linear speed recording (for example, Japanese Patent laid open Publication 5-298747/1993, Japanese Patent Publication 8-1707/1996, Japanese Patent laid open Publications 7-78354/1995 and 7-262612/1995). In all the proposals, the light absorptance of the recording thin film for the laser beam for recording is larger in the crystalline state than in the amorphous state of the recording thin film.
For an ordinary phase-change type optical disk without the optical absorption correction, the absorptance of the recording thin film for a laser beam for recording is smaller in the crystalline state than in the amorphous state. For such an optical disk, it is known that the temperature of the recording thin film attained on melting with the laser beam becomes higher in an area which was amorphous before the laser irradiation than in an area which was crystalline before the laser irradiation. This is ascribed to that latent heat is not needed to be supplied on melting from a starting point of the crystalline state but not so from a starting point of the amorphous state. It is also ascribed to that the amorphous state can be heated efficiently to a higher temperature because the thermal conductivity is lower in the amorphous state than in the crystalline state. Further, for an optical disk without the optical absorption correction, a large difference on the temperature attained on melting arises especially on high linear velocity recording. The reason is that a temperature rise effect other than the direct temperature rise due to laser irradiation, that is, temperature rise due to heat diffusion around the laser irradiation point, is smaller than the counterpart in low linear velocity recording. If the temperature attained on melting is changed according as the recording thin film was amorphous or crystalline before laser irradiation for recording, or according as it is a recorded mark or a non-recorded region, the shape of a recorded mark formed newly by overwriting is distorted, and good reproduction jitter cannot be obtained. The optical absorption correction is proposed for realizing good overwrite characteristic on high linear velocity recording by canceling the above-mentioned difference in temperature rise profile depending on whether the recording thin film is amorphous or crystalline.
Further, in order to increase the recording density of an optical disk on which recording is possible or an optical disk on which both recording and erasing are possible, so-called land and groove recording is proposed, wherein signals are recorded on grooves formed on the substrate surface and on lands between the grooves (for example, Japanese Patent laid open Publication 5-282705/1993).
Further, in order to increase the recording capacity of an optical disk on which both recording and erasing are possible, a two-layers structure is already proposed wherein information is read from one side thereof (for example, Japanese Patent laid open Publication 9-212917/1997). The optical disk of two-layers structure has two phase-change recording films, and information is read or erased in each of the recording films by irradiating a laser beam from one side of the optical disk. The recording capacity is increased twice by using two recording films. As to the initialization of an optical disk of the two-layers structure, it is proposed to shorten the initialization time by irradiating the two recording layers at the same time (for example, Japanese Patent laid open Publication 9-91700/1997).
Though the idea of the two-layers structure of an optical disk on which both recording and erasing are possible is already proposed (for example, Japanese Patent laid open Publication 9-212917/1997) in order to enhance the recording capacity, it has not yet been used practically because following problems are not solved. Hereinafter, “first information layer” denotes a recordable layer positioned at the front side viewed from the incident laser beam for recording and reproduction, and “second information layer” denotes a recordable layer positioned at the back side viewed from the incident laser beam.
1) A structure of the first information layer is not known, that has high transmittance, and high recording sensitivity at a laser beam wavelength for recording, erasing and reproducing signals, that enables land and groove recording, and that has a good repetition characteristic of recording and erasing.
2) A structure of the second information layer is not known, that has high recording sensitivity and sufficiently high reflectance at non-recorded portions at a laser beam wavelength for recording, erasing and reproducing signals, that enables land and groove recording, and that has a good repetition characteristic of recording and erasing.
3) A structure of the two-layers optical disk is not known that enables high speed overwriting to the first and second information layers.
4) In the initial crystallization of the optical recording medium having two layers of phase-change recording thin films, the sensitivity of the initial crystallization is different among the first and second information layers, and it is necessary to perform the initialization at different initialization conditions. Though the initialization with focus servo for each information layer is proposed (for example, Japanese Patent laid open Publication 9-91700/1997), this needs an optical system having the focal depth narrower than the thickness of the separation layer. Therefore, this is a problem for an apparatus for high speed initialization by laser irr
Akahira Nobuo
Nagata Ken'ichi
Nishiuchi Ken'ichi
Yamada Noboru
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
Young W. R.
LandOfFree
Optical information recording medium comprising a first... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical information recording medium comprising a first..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical information recording medium comprising a first... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2883289