Dynamic information storage or retrieval – Systems having plural physically distinct independent tracks... – Having layered storage medium
Reexamination Certificate
2000-06-29
2004-05-18
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Systems having plural physically distinct independent tracks...
Having layered storage medium
C369S275100, C369S288000
Reexamination Certificate
active
06738335
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-186535, filed Jun. 30, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an optical recording medium, a reproducing method, and a reproducing apparatus and, more particularly, to an optical recording medium having a structure in which a plurality of recording layers are stacked, and a reproducing method and apparatus for the medium.
Optical recording media such as optical disks are used in various forms. For example, as external storage media of computers and as music media, CDs (Compact Discs) such as CD-ROM (read only), CD-R (write-once), and CD-RW (rewritable) are extensively used. Also, DVDs (Digital Versatile Discs) are becoming popular as optical recording media having larger capacity and are used in video recording, in computer storaging, and the like in recent years. DVDs also have diverse types: DVD-ROM (read only), DVD-R (write-once), and DVD-RAM (rewritable).
Of these optical recording media, a read only medium, for example, has a recording layer in which pits having a depth ¼ the wavelength of a laser beam are formed as recording marks. When this pit is irradiated with a laser beam, the phase of reflected light from the pit shifts by ½ from that of reflected light from the periphery of the pit. Consequently, these reflected light components produce interference. Therefore, compared to the case in which a portion having no pit is irradiated with a laser beam, the intensity of reflected light detected by a photodetector lowers. A read only optical recording medium uses this principle in reproducing recorded information.
DVDs have a structure in which a pair of disks each having a thickness of 0.6 mm are adhered. A DVD in which recording layers are formed on both opposing surfaces of these disks is called a dual-layered DVD. Of such dual-layered DVDS, a DVD that allows information recorded in a pair of recording layers to be read out from one side is called a single-sided, dual-layered DVD.
FIG. 1
is a sectional view schematically showing a conventional single-sided, dual-layered DVD. As shown in
FIG. 1
, this conventional single-sided, dual-layered DVD
101
has a structure in which a substrate
102
having a recording layer
104
on one principal surface and an opposing substrate
103
having a recording layer
105
on one principal surface are adhered via an interlayer
106
such that the recording layers
104
and
105
oppose each other. Note that the recording layer
104
is a semitransparent film and the recording layer
105
is a reflecting film.
Information recorded in the recording layer
104
of this conventional single-sided, dual-layered DVD
101
is read out by sending a laser beam
107
, focused on the recording layer
104
, from the side of the substrate
102
, and detecting the intensity of the reflected light by a photodetector. Although reflected light from the recording layer
105
is also detected, the focal depth of this layer beam
107
is small, so the intensity of the reflected light from the recording layer
105
is much lower than that of the reflected light from the recording layer
104
. Accordingly, only the information recorded in the recording layer
104
can be selectively read out.
On the other hand, to read out information recorded in the recording layer
105
, a laser beam
108
focused on the recording layer
105
is sent from the side of the substrate
102
. As in the above case, only the information recorded in the recording layer
105
can be selectively read out.
In this prior art as described above, in reading out information recorded in one of the recording layers
104
and
105
, information recorded in the other is prevented from becoming noise by using the small focal depth of the laser beam used to read out information. This allows read-out of information recorded in the recording layers
104
and
105
. Hence, in this prior art it is necessary to move the focal position of the laser beam.
To move the focal position, a mechanism for moving a lens must be incorporated into an optical disk drive. This significantly increases the time and cost necessary to manufacture the optical disk drive of this prior art. Also, when the focal position is thus moved, reading out recorded information naturally requires a long time. Accordingly, it is difficult for this prior art to realize a high read rate.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to make it possible to read out information recorded in a single-sided, multilayered optical recording medium at high speed.
It is another object of the present invention to reduce the cost and time required to manufacture a reproducing apparatus for a single-sided, multilayered optical recording medium.
According to the first aspect of the present invention, there is provided an optical recording medium using a reflectance difference to reproduce recorded information, comprising a first recording layer, an interlayer provided on one principal surface of the first recording layer, and a second recording layer provided on the interlayer, wherein the interlayer guides converged light irradiating the first recording layer to the second recording layer such that a beam diameter of the light on the second recording layer is substantially equal to a beam diameter of the light on the first recording layer.
According to the second aspect of the present invention, there is provided an optical recording medium using a reflectance difference to reproduce recorded information, comprising a first recording layer, an interlayer provided on one principal surface of the first recording layer and made of a third-order nonlinear optical material, and a second recording layer provided on the interlayer.
According to the third aspect of the present invention, there is provided an optical recording medium using a reflectance difference to reproduce recorded information, comprising a first recording layer, an interlayer provided on one principal surface of the first recording layer, and a second recording layer provided on the interlayer, wherein the interlayer comprises first and second portions juxtaposed on the first recording layer, and a refractive index of the second portion is higher than that of the first portion.
According to the fourth aspect of the present invention, there is provided a reproducing method of an optical recording medium comprising a first recording layer, an interlayer provided on one principal surface of the first recording layer, and a second layer provided on the interlayer, comprising the steps of irradiating the first recording layer with converged light, and detecting the intensity of reflected light produced by irradiation of the converged light, wherein the interlayer guides the converged light irradiating the first recording layer to the second recording layer such that a beam diameter of the light on the second recording layer is substantially equal to a beam diameter of the light on the first recording layer.
According to the fifth aspect of the present invention, there is provided a reproducing apparatus of an optical recording medium having a structure in which a plurality of recording layers are stacked, comprising an optical recording medium comprising a first recording layer, an interlayer provided on one principal surface of the first recording layer, and a second recording layer provided on the interlayer, a light source for irradiating the first recording layer with converged light, and a detector for detecting the intensity of reflected light produced by irradiation of the light, wherein the interlayer guides the converged light irradiating the first recording layer to the second recording layer such that a beam diameter of the light on the second recording layer is substantially equal to a beam diameter of the light on the first recording layer.
The term “reflectance” means a value actual
Ichihara Katsutaro
Nagase Toshihiko
Todori Kenji
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tran Thang V.
Vuong Bach
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