Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2000-02-04
2003-01-28
Angebranndt, Martin (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S945000, C428S064500, C369S284000, C369S275200, C369S275500
Reexamination Certificate
active
06511788
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Application No. P11-035086 filed Feb. 12, 1999 which application is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a multi-layered optical disc having its recording unit comprised of plural information recording layers. More particularly, it relates to a multi-layered optical disc having its information recording layer formed of a phase change material.
2. Description of Prior Art
Recently, as so-called multi-media are becoming popular, a demand is raised for an optical recording medium handling a large volume of the information, such as a digital moving picture, such that the necessity of storing the large volume of the information and having a random access thereto as necessary for recording and/or reproduction is increasing.
Among the random-accessible recording mediums, there is an optical recording medium of a large storage capacity which is removable, that is can be taken out from the recording and/or reproducing apparatus. This optical recording medium is used in large quantities in many fields.
Under these circumstances, an optical recording medium on one surface of which recording and/or reproduction for four hours is possible in accordance with the NTSC (National Television System Committee) system.
In this optical recording medium, it is targeted to enable recording and/or reproduction for four hours, as a video disc player for home use, to provide a function as a new recording medium which takes the place of the video tape recorder now in prevalent use. Moreover, the optical recording medium may be of the same shape and size as the digital audio disc, having the music data recorded thereon, to prove a product more benign to a user accustomed to a digital audio disc.
Meanwhile, a demand is raised for an optical recording medium capable of handling a still larger information volume, such that the optical recording medium is required to have a still larger storage volume.
For example, the optical recording medium, capable of recording and/or reproduction in accordance with the NTSC system, is required not only to be in a disc shape to exploit the high accessing speed proper to the disc shape to provide a simple and small-sized recording medium, but also to be of a large storage capacity to have multiple functions such as instant reproduction of a recorded picture, trick play or editing.
In order to have these variegated functions, the capacity not less than 8 GB is required. However, there lacks up to now an optical recording medium capable of realizing this large storage capacity by the following reason:
In the already proposed replay-only DVD (digital versatile disc), the wavelength &lgr; is 0.65 &mgr;m, with the numerical aperture NA of the optical system being 0.6, such that the recording capacity possible with the current DVD is not above 4.7 GB.
Thus, in order to provide a recording capacity not less than 8 GB, with the signal format of the DVD system, such as ECC (error correction code) or the modulation system, remaining unchanged, the following relation:
4.7×(0.65/0.60×NA/&lgr;)2≧8 (1)
needs to be met.
From the equation (1), it is necessary that NA/&lgr;≧1.20, such that a shorter wavelength or a larger magnitude of NA is required.
If the NA is of a larger magnitude, a transparent substrate of the optical disc, through which the illuminated reproducing light is transmitted, needs to be reduced in thickness. The reason is that, as NA is increased, the allowance for the aberration ascribable to an angle by which the disc surface deviates from the vertical with respect to an optical axis of the optical pickup, or the so-called tilt angle, becomes smaller, with the aberration ascribable to this tilt angle increasing with the increased thickness of the transparent substrate through which is transmitted the reproducing light.
By the same reason, variations in the thickness of the transparent substrate, through which is transmitted the reproducing light, need to be comprised within a pre-set range.
Meanwhile, an injection molded substrate, formed of plastics, is prevalently used as the transparent substrate for the optical recording medium. This injection molded substrate is difficult to manufacture with an extremely thin thickness and to a high accuracy.
On the other hand, the recording density of the information recording layer of an optical recording medium in an in-plane direction, that is in a two-dimensional direction, is determined by the minimum spot diameter of the laser light in use. Thus, the smaller the minimum spot diameter, the higher may be the density with which the signals are recorded. Therefore, in order to enable high density recording on an optical recording medium, it is attempted to reduce the wavelength of the light source and to increase the numerical aperture NA of the objective lens to reduce the minimum spot diameter. However, there is imposed a technical limitation in shortening the wavelength of the laser light or in increasing the numerical aperture NA of an objective lens, such that increasing the recording density in the two-dimensional direction is approaching its limit.
As means for increasing the recording capacity in an optical disc, there are such method as increasing the number of the recording layers, in addition to the methods of further reducing the recording and/or reproducing wavelength or improving the light converging power (NA) of the light used for recording and/or reproduction. In the write-once or overwrite optical disc, the preference is towards reducing the recording and/or reproducing wavelength and towards a higher NA of the objective lens, whilst multi-layered optical disc was first introduced in Society Publications only in October 1998.
The purport of this report was that recording and/or reproduction is possible in both the two phase change recording layers. It is however feared whether or not, if the information has been recorded on the light incident side recording layer (first recording layer), no information has been recorded on the first recording layer or if a recorded region and a non-recorded region co-exist in the first recording layer, recording can be made in stability in the other recording layer (second recording layer). In actuality, with the phase change recording material, it has been demonstrated that light transmittance of the first recording layer is higher in the recorded state, that is in the amorphous state, than in the non-recorded state, that is in the crystalline state, of the recording material. According to the reports, the light transmittance of the first recording layer is 70% and 45% in the crystalline state and in the amorphous state, respectively.
If the light transmittance of the first recording layer is varied appreciably before and after recording on this layer, it is necessary to record the information on the second recording layer after recording the information on the entire surface of the first recording layer. However, since signals cannot be recorded nor reproduced freely on each of the first and second recording layers, there are imposed severe limitations on the information exchange with the media, with the result that the merit proper to the multi-layered optical disc tends to be lost. Moreover, the transfer rate of the information recorded or reproduced on or from an optical disc recently is desired to be increased, so that an increasing demand is raised for simultaneously recording and/or reproducing plural recording layers of the multi-layered optical disc to increase the transfer rate by a factor corresponding to the number of the recording layers.
Moreover, if, in a recording and/or reproducing optical disc having layered information recording layers, the linear speed in raised by reducing the beam spot diameter, difficulties may be encountered in correctly recording the data, so that, if two information recording layers are layered, it has been difficult to re
Kurokawa Kotaro
Yasuda Koichi
Angebranndt Martin
Sonnenschein Nath & Rosenthal
Sony Corporation
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