Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
2000-10-18
2002-12-03
Neyzari, Ali (Department: 2653)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S275300
Reexamination Certificate
active
06490239
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disc having an effect of indicating characters and pictures by making use of light diffraction.
2. Description of the Related Art
There has been known a technique in which diffracted light, caused by pits formed on one surface of an optical disc, can be used to indicate characters and pictures on the surface of the disc. In industry, such a technique is usually referred to as a mastering art or a pit art. In practice, when a mastering art disc is formed by bonding together two single-plate discs, such as in a process in which a DVD is manufactured, the outer surface of one of the two single-plate discs is used as a label-indication surface to indicate characters and pictures, so that the title of the DVD may be expressed thereon.
Further, there have been suggested various methods for manufacturing an optical disc using mastering art. However, in practice, a stamper for forming such an optical disc may be manufactured with the use of a conventional mastering process that includes the following steps and will be described as below. (1) A photoresist is applied on to the surface of a master disc made of a glass so as to form a resist layer thereon. (2) A laser cutting machine is used to produce a laser pulse so as to intermittently irradiate the glass-made master disc to form latent pit images on the resist layer. (3) A developing treatment is carried out and some exposed portions of the resist layer are removed. (4) A conductorizing treatment is carried out to form a conductive film on the surface of the resist layer and on some portions of the master disc from which the resist substance has been removed. In detail, the conductive film may be formed by a metal such as Ni, with the use of a film formation process such as electroless plating, sputtering or vapor deposition. (5) An electrocasting treatment is carried out to form a metal layer such as an Ni layer over the conductive film, the electrocasting treatment being continued until a metal layer having a predetermined thickness is formed. (6) The metal layer is removed from the glass-made master disc. (7) The back surface of the metal layer is polished and is then subjected to a pressing treatment so as to form a predetermined outer diameter and a predetermined inner diameter.
Here, the above step (2) will be described in more detail with reference to
FIGS. 1 and 2
. For example, as shown in
FIG. 1
, when a character “K” represented by a pattern
103
is indicated in the recording area of an optical disc stamper, pits are not formed in an area
102
of the pattern
103
, but are formed in an area
101
excluding the area
102
.
FIG. 2
is an enlarged view schematically indicating the area
101
. In the step (2), the glass-made master disc is rotated, and the laser beam is linearly moved in the radial direction of the disc in a manner such that the area
102
is not exposed while the area
101
is exposed by an intermittently produced pulse. In this way, a stamper made in this step is formed with a spiral track
202
with the rotation center
104
serving as its spiral center, thereby forming many pits
201
at a predetermined interval along the track
202
.
Further, when an optical disc is manufactured based on the stamper, it can use the same method as used for manufacturing a common optical disc. Namely, after a resin such as polycarbonate is injection molded, a sputterring apparatus is used to form a reflecting film such as an AlTi film on one surface of the disc having a plurality of pits formed thereon.
FIG. 3
is a view schematically indicating a cross section of an optical disc in its circumferential direction (direction &thgr; in FIG.
1
). As shown in
FIG. 3
, a plurality of pits
305
formed on a stamper at a predetermined interval have been transferred on to one surface of a polycarbonate substrate plate
301
. A reflecting film
302
is formed on that same surface of the substrate plate. Here, a center-to-center interval between every two pits is set to be P. Light rays
303
incident on the substrate plate
301
have various spectral characteristics due to different environments. However, the light ray used here is set to be a white light containing equivalently all the light components having various different wavelengths in the range of the visible light. Here, if P is set to be about 1 &mgr;m, the light ray
303
passing through the substrate plate
301
will be reflected by the reflecting film
302
, thereby obtaining a reflected light. At this time, only some light rays of the reflected light having a specific wavelength in a specific direction will be strengthened by each other, so that these light rays become diffracted light
304
and are allowed to emit outwardly through the substrate plate
301
.
FIG. 4
is an explanatory view schematically showing a positional relationship between the diffracted light (represented by reference numeral
304
shown in
FIG. 3
) from the optical disc
401
on one hand and the position of a viewer on the other. As shown in the figure, the head of an observer
402
is located in the normal line direction of an optical disc
401
, so that the observer can observe the optical disc
401
from an upper position above the disc. Here, the observer
402
is assumed to be in a typical living environment, and the light ray
303
is assumed to be a white light ray. Further, the diffracting angles of the diffracted light rays
304
to be observed will be different from one another depending upon their different positions on the optical disc. Further, since the light rays
303
may also be considered to have various different incident angles, various diffracted light rays
304
having different wavelengths can be observed as if a rainbow-like image is formed on the surface of the optical disc.
In this way, by virtue of the above-described diffraction, within the surface of the optical disc
401
, the area
101
having pits formed thereon can be observed to -have bright rainbow colors. On the other hand, the area
102
having no pits formed thereon will be observed to have a dark color since there is no diffraction occurring thereon. By virtue of such a contrast, a character like “K” shown in
FIG. 1
will become clearly visible.
OBJECTS OF THE INVENTION
In order to clearly indicate pictures or characters formed on an optical disc, it is desirable that the diffracted light rays in the area where the pits are formed be bright enough to be clearly observed. In the above example, the wavelength of each diffracted light
304
and the light amount thereof will depend upon the interval between every two pits and pit shape. Further, since people will have different perceptions of different wavelengths of visible lights rays, and since it is desired to clearly observe the diffracted light rays, a suitable pit interval and pit shape is required.
An object of the present invention is to solve the above described problems and a specific object is to calculate the best pit interval and best pit shape that are effective for obtaining a maximum light amount of diffracted light rays, thereby making it possible to clearly indicate any pictures or characters formed on a mastering art disc.
SUMMARY OF THE INVENTION
According to the present invention, it is possible to provide the following first to third types of optical discs.
A first type optical disc according to the present invention has a circular disclike substrate including areas on which a plurality of pits or grooves have been formed, such disc having an effect of indicating characters and pictures by making use of a property in which incident light irradiating the pits or grooves will be diffracted, characterized in that: an interval Pr (nm) between every two pits or every two grooves in the radial direction of the optical disc is 570≦Pr≦1000.
A second type optical disc according to the present invention has a circular disc-like substrate including areas on which a plurality of pits or grooves have been formed, such disc having an effect
Neyzari Ali
Seiko Epson Corporation
Watson Mark P.
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