Optical recording medium and optical disk device

Details Optical recording medium and optical disk device Optical recording medium and optical disk device

1999-06-09

2002-03-05

Hudspeth, David (Department: 2651)

Dynamic information storage or retrieval

Storage medium structure

Layered

C369S286000, C369S275500, C428S064400, C430S271100

Reexamination Certificate

active

06353592

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an optical recording medium and in particular, to an optical recording medium including a recording layer made from a metal reflection film and/or recording film and a light-transmitting layer formed on a substrate so that light is introduced from the side of this light-transmitting layer for performing an information recording and/or reproduction.
BACKGROUND ART
A conventional optical recording, as shown in
FIG. 25
, has a concave-convex pattern such as a pit and a groove formed on one main surface
121
a
on a light-transmitting substrate
121
formed by injection molding, and on the plane of this concave-convex pattern, a metal reflection film and/or recording film (metal reflection film
122
in this case), and protection film
123
are successively formed. In such an optical recording medium
120
, light is introduced via an objective lens
124
from a surface
121
b
of the substrate
121
not having the protection film
123
, so as record and/or reproduce an information signal.
As the method for further increasing the recording density of the optical recording medium, there has been suggested a method for increasing the numerical aperture of the optical pickup objective lens so as to reduce the spot diameter of the reproduction light and to perform recording according to this.
Recently, a DVD (digital versatile disc, hereinafter, referred to as DVD) is also available in market for recording various types of data such as images, music, computer data and the like. In this DVD, the substrate has a thickness in the order of 0.6 mm to cope with a short wavelength optical system having a high numerical aperture for realizing a high-density recording.
In such circumstances, as an optical recording medium of the next generation, Japanese Patent Application 9-109660, Specification, has suggested an optical recording medium capable of four-hour recording/reproduction on one side by the NTSC (National Television System Committee) method.
This optical recording medium, enabling a civil video disc recorder to perform 4-hour recording/reproduction, has an object to have a function as a new recording medium to replace the current video tape recorder. Moreover, this optical recording medium has a configuration and size identical to that of a digital audio disc so that it can easily be handled by users who are accustomed to use digital audio discs. Furthermore, when this optical recording medium is a disc-shaped product, it is possible to utilize the high access speed which is the greatest feature of the disc shape, realizing a small-size convenient recording medium. It is also possible to provide various functions such as an instantaneous recording and reproduction as well as a trick play and edition.
The aforementioned optical recording medium need to have a recording capacity of 8 GB or more for providing such various functions.
However, in the conventional optical recording medium, especially when the size is identical to that of a digital audio disc and the information recording layer is provided only on one side, it is impossible to obtain 8-GB recording capacity. For example, in the case of DVD considered to have a high recording capacity, an information signal section area, i.e., in a region of radius of 24 to 58 mm from the center, only 4.7-GB recording capacity can be obtained, assuming the wavelength &lgr; to be 0.65 micrometers and the optical system numerical aperture (hereinafter, referred to as NA) to be 0.6.
For example, in order to assure a recording capacity of 8 GB or more using the DVD format as the signal format such as the ECC (error correction code) and modulation method, it is necessary to satisfy the following Expression 1.
4.7×(0.65/0.60×NA/&lgr;
2
≧82 . . .   (1)
According to this Expression 1, NA/lamda should be equal to or greater than 1.20. That is, it is necessary to reduce the wavelength or increase the NA.
Here, for example, if the NA is increased, it is necessary to reduce the thickness where the reproduction light transmits. This is because increase of the NA reduces the allowance of the aberration generated by the angle of the disc surface displaced from the vertical direction with respect to the optical pickup optical axis (a so-called tilt angle, proportional to the square of the product of the reverse number of the light source wavelength by the objective lens NA). This tilt angle is easily affected by the aberration due to the substrate thickness. Accordingly, the substrate thickness is reduced so as to minimize the affect from the aberration to the tilt angle.
Moreover, for the same reason, the fluctuation of thickness where the reproduction light transmits should also be within a predetermined range.
It is considered that a further higher recording density will be required in future with reduction in the substrate thickness. To cope with this, a shown in
FIG. 26
, there has been suggested an optical recording medium
130
including a convex-concave pattern formed on a substrate
131
whose main surface
131
a
is covered with a metal reflection film and/or recording film (here, metal reflection film
132
), and a light-transmitting layer
133
formed successively in this order, so that light is applied from the side of this light-transmitting layer
133
for recording and/or reproducing an information signal. In this optical recording medium
130
, the light-transmitting layer
133
is made thin to answer the high NA of the objective lens
134
. On the other hand, in an optical recording medium, sometimes an inclination (hereinafter, referred to as a skew) of the optical recording medium with respect to the optical axis is generated to affect the signal characteristic.
This skew is usually caused by a warp of the substrate itself due to the injection molding, shrinkage of the protection film formed on the substrate, or warp of the substrate due to water absorption.
The skew present in the optical recording medium immediately after production is called initial skew. This initial skew has a configuration determined by the relationship of the force of the substrate and the force of the protection film formed. This initial skew is changed by mitigation of the stress inside the substrate and the hardening of the protection film to be stabilized finally. Furthermore, the skew due to the warp of the substrate itself and shrinkage of the protection film is changed with lapse of time for a long period of time.
On the other hand, the water absorption amount of the substrate is changed by an environmental change such as a temperature change and a humidity change. The water absorption may expand the substrate, generating a skew. Such a skew caused by an environmental change, especially the skew caused by water absorption is often seen in an optical recording medium having a signal plane only on one side, i.e. asymmetric configuration. This is because the optical recording medium having asymmetric configuration has water absorption varied over the substrate. Such a skew caused by water absorption is present in a transient condition such as water absorption and water discharge and disappears when the environment is stabilized.
The problem of the aforementioned skew in the optical recording medium, especially the skew due to water absorption is solved by waiting for half day or so. In case of a reproduction-dedicated medium, reproduction may be disabled temporarily but the medium returns to a reproduction-enabled state after waiting half day.
However, when the medium is for both of recording and reproduction, it becomes impossible to perform preferable recording and reproduction. Especially, recording cannot be performed at a desired moment and the user must miss a scene that he/she wants to record. Accordingly, in an optical recording medium capable of recording, this skew should be suppressed.
As a method to suppress the skew due to water absorption in the conventional optical recording medium
120
as shown in
FIG. 25
, a water-proof film can be formed on a main surface
121
b
of

Affiliated with

Also associated with

Rating

Optical recording medium and optical disk device 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 recording medium and optical disk device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical recording medium and optical disk device will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2829786