Dynamic information storage or retrieval – Storage medium structure – Layered
Reexamination Certificate
2003-04-14
2004-08-03
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
Storage medium structure
Layered
C369S275400
Reexamination Certificate
active
06771587
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical information recording medium capable of reproducing information signals or recording and reproducing information signals by using light beams, a manufacturing method therefor, a manufacturing apparatus therefor and an optical information recording and reproducing apparatus making use thereof, and more particularly to an optical information recording medium having a multilayer structure including a plurality of information layers, a manufacturing method therefor, a manufacturing apparatus therefor and an optical information recording and reproducing apparatus making use thereof.
DESCRIPTION OF THE PRIOR ART
Hitherto, an optical information recording medium has been known which is capable of optically recording information signals or reproducing recorded information signals and which is formed into an optical disk, an optical card or the like. In general, the foregoing recording medium uses a semiconductor laser unit as a light source. By irradiating the recording medium with light beams finely converged by a lens, information signals can be recorded on the recording medium in a large quantity, and information signals recorded on the recording medium can be reproduced.
At present, investigations have been performed to further enlarge the recording capacity of the recording medium of the foregoing type. To raise the recording density, it is effective to improve the reproducing resolution by finely limiting the light beam. In order to achieve this, investigations have been performed such that the wavelength of the light beam is shortened or the numerical aperture (NA) is enlarged. Moreover, reproducing methods have been investigated in which the focusing or tracking accuracy is improved and crosstalk between signals is prevented so as to allow the recording surface density to be raised.
Although employment of the foregoing methods enables the recording capacity per unit area to be somewhat enlarged, a structure having only a single information layer for recording information encounters a limitation when the recording density is intended to be raised.
If a plurality of information layers for recording information are provided, it can be expected that the recording capacity can be multiplied. A method for manufacturing an optical disk having the multilayer structure has been disclosed in, for example, U.S. Pat. No. 5,126,996.
A process for manufacturing the foregoing optical disk will now be described. As shown in FIG.
21
(
a
), a first information layer
212
is formed on the surface of a substrate
211
manufactured by an injection molding method or the like and having information pits. Then, as shown in FIG.
21
(
b
), a photosetting resin
214
is applied to the upper surface of a master
213
having information pits. Then, as shown in FIG.
21
(
c
), the surface of the first information layer
212
on the substrate
211
having the information pits and the surface of the master
213
having the information pits are caused to face each other. Then, in a state where the substrate
211
is pressed, the photosetting resin
214
is irradiated with light from a position on the outside of the master
213
. As a result, the photosetting resin
214
is set so that the photosetting resin
214
is adhesive-bonded to the first information layer
212
. Then, as shown in FIG.
21
(
d
), the master
213
is removed from the photosetting resin
214
. As a result, a resin layer having information pits on the surface thereof and composed of the photosetting resin
214
can be formed. Then, as shown in FIG.
21
(
e
), a second information layer
215
is formed on the resin layer (made of the photosetting resin
214
). Finally, as shown in FIG.
21
(
f
), a protective coating layer
206
is formed on the second information layer
215
. As a result of the foregoing process, an optical disk having a double-layer structure can be obtained.
However, when the master
213
is separated from the photosetting resin
214
(see FIG.
21
(
d
)), the foregoing conventional manufacturing method can involves separation being easily taking place at the interface between the first information layer
212
and the substrate
211
or the resin layer (made of the photosetting resin
214
). Thus, there arises a problem in that the manufacturing yield has been unsatisfactory. The reason for this can be considered that the adhesivity between the master
213
and the resin layer (made of the photosetting resin
214
) is made to be greater than that between the first information layer
212
and the substrate
211
or that between the first information layer
212
and the resin layer (made of the photosetting resin
214
).
In a case where the substrate
211
is made of a resin, change in the environmental temperature or in the humidity sometimes raises a problem in that the manufactured optical disk can be deformed or an error occurs in reproducing the signals.
Moreover, an apparatus of a type for reproducing information signals from a plurality of information layers has a problem in that the servo operation becomes instable due to an influence of light reflected by an information layer other than the subject information layer.
SUMMARY OF THE INVENTION
The present invention was found to overcome the foregoing problems experienced with the conventional structure, and, therefore, an object of the present invention is to provide an optical information recording medium having a multilayer structure which cannot easily be deformed due to change in the environment, a manufacturing method therefor, a manufacturing apparatus therefor and an apparatus for optically recording and reproducing information.
To achieve the foregoing object, according to one aspect of the present invention, there is provided an optical information recording medium having two different information layers and capable of reproducing information signals from the information layers, recording information signals on the information layers that can reproduce the recorded information signals when irradiated with a light beam, the optical information recording medium comprising: a first substrate having, on one side thereof, one or more selected from the group consisting of information pits corresponding to information signals, guide grooves for tracking and sample pits; a first information layer formed on either surface of the first substrate and having a predetermined transmissivity and a predetermined reflectance with respect to the light beam; a second substrate having, on one side thereof, one or more selected from a group consisting of information pits corresponding to information signals, guide grooves for tracking and sample pits; a second information layer formed on either surface of the second substrate and having a predetermined reflectance; and a separation layer formed between the first information layer and the second information layer that is transparent with respect to the light beam. The structure of the optical information recording medium provides a double-layer recording medium that is capable of reproducing information signals from the first and second information layers, recording information signals on the first and second information layers and reproducing recorded information signals.
It is preferable that the optical information recording medium according to the present invention has a structure such that the thickness of the first substrate is substantially the same as the thickness of the second substrate. As a result of the preferred structure, a structure vertically symmetrical with respect to the separation layer can be formed. Therefore, even if stress or the like is generated in the substrate due to change in the temperature or the like when the optical information recording medium is manufactured, distortion can be compensated. Even if unusual deformation factors act on the two substrates due to change in the temperature or the humidity of the environment, deformation and warp can be inhibited. As a result, a structure durable against change in the environment c
Akahira Nobuo
Nagata Ken'ichi
Nishiuchi Ken'ichi
Huber Paul W.
Merchant & Gould P.C.
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