U.S. patent application number 12/814091 was filed with the patent office on 2011-03-10 for optical information storage medium reproduction apparatus and control method of the same.
This patent application is currently assigned to SHARP KABUSHIKI KAISHA. Invention is credited to Yasuhiro Harada, Shigemi Maeda, Go Mori, Yoshiteru Murakami, Hideharu Tajima, Hirohisa Yamada, Masaki Yamamoto.
Application Number | 20110058460 12/814091 |
Document ID | / |
Family ID | 40567267 |
Filed Date | 2011-03-10 |
United States Patent
Application |
20110058460 |
Kind Code |
A1 |
Yamamoto; Masaki ; et
al. |
March 10, 2011 |
OPTICAL INFORMATION STORAGE MEDIUM REPRODUCTION APPARATUS AND
CONTROL METHOD OF THE SAME
Abstract
In an optical information storage medium reproduction apparatus
(10) for reproducing an optical information storage medium
including a plurality of information recording layers each
including a recording mark having a length shorter than an optical
system resolution limit, reproduction laser power for reading an
information recording layer closest to a
reproduction-laser-incident surface of the optical information
storage medium is set to be lower than reproduction laser power for
reading an information recording layer farthest from the
reproduction-laser-incident surface but not lower than minimum
reproduction laser power that satisfies a reproduction signal
characteristic that the optical information storage medium
reproduction apparatus (10) requires. With the arrangement, it is
possible to prevent that the information recording layer closest to
the reproduction-laser-incident surface is irradiated wrongly with
reproduction laser having high reproduction laser power, thereby
making it possible to obtain successful reproduction quality. That
is, it is possible to realize the optical information storage
medium reproduction apparatus (10) that can set optimum
reproduction laser power and perform stable super resolution
reproduction.
Inventors: |
Yamamoto; Masaki; (Osaka,
JP) ; Yamada; Hirohisa; (Osaka, JP) ; Harada;
Yasuhiro; (Osaka, JP) ; Mori; Go; (Osaka,
JP) ; Tajima; Hideharu; (Osaka, JP) ; Maeda;
Shigemi; (Osaka, JP) ; Murakami; Yoshiteru;
(Osaka, JP) |
Assignee: |
SHARP KABUSHIKI KAISHA
Osaka
JP
|
Family ID: |
40567267 |
Appl. No.: |
12/814091 |
Filed: |
June 11, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12734169 |
Apr 14, 2010 |
|
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PCT/JP2008/067327 |
Sep 25, 2008 |
|
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12814091 |
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Current U.S.
Class: |
369/47.5 ;
369/100; G9B/7 |
Current CPC
Class: |
G11B 7/08511 20130101;
G11B 7/12 20130101; G11B 7/24 20130101; G11B 7/126 20130101; G11B
19/128 20130101; G11B 19/125 20130101; G11B 7/005 20130101; G11B
7/0037 20130101; G11B 7/24038 20130101; G11B 7/1263 20130101; G11B
7/00 20130101; G11B 2007/0013 20130101 |
Class at
Publication: |
369/47.5 ;
369/100; G9B/7 |
International
Class: |
G11B 7/00 20060101
G11B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 19, 2007 |
JP |
273204/2007 |
Claims
1. An optical information storage medium reproduction apparatus for
reproducing an optical information storage medium in which a
plurality of information recording layers are laminated, each of
the plurality of information recording layers including a recording
mark having a length shorter than an optical system resolution
limit, wherein: the optical information storage medium reproduction
apparatus reads an information recording layer closest to a
reproduction-laser-incident surface of the optical information
storage medium, with reproduction laser power that is set to be
lower than reproduction laser power for reading an information
recording layer farthest from the reproduction-laser-incident
surface but not lower than minimum reproduction laser power that
satisfies a reproduction signal characteristic that the optical
information storage medium reproduction apparatus requires.
2. An optical information storage medium reproduction apparatus for
reproducing an optical information storage medium in which a
plurality of information recording layers are laminated, each of
the plurality of information recording layers including a recording
mark having a length not longer than 120 nm, the optical
information storage medium reproduction apparatus comprising: an
optical system including a laser light source capable of
irradiating laser light having a wavelength of not less than 400 nm
but not more than 410 nm and an objective lens having a numerical
aperture of not less than 0.83 but not more than 0.87, wherein: the
optical information storage medium reproduction apparatus reads an
information recording layer closest to a
reproduction-laser-incident surface of the optical information
storage medium, with reproduction laser power that is set to be
lower than reproduction laser power for reading an information
recording layer farthest from the reproduction-laser-incident
surface but not lower than minimum reproduction laser power that
satisfies a reproduction signal characteristic that the optical
information storage medium reproduction apparatus requires.
3. The information recording medium reproduction apparatus as set
forth in claim 1 or 2, wherein: the reproduction laser power with
which the optical information recording medium reproduction
apparatus reads the information recording layer closest to the
reproduction-laser-incident surface is set to be not higher than
0.95 times the reproduction laser power for reading the information
recording layer farthest from the reproduction-laser incident
surface but not lower than 1.05 times the minimum reproduction
laser power that satisfies the reproduction signal characteristic
that the optical information storage medium reproduction apparatus
requires at the time of reading the information recording layer
closest to the reproduction-laser-incident surface.
4. The optical information storage medium reproduction apparatus as
set forth in any one of claims 1 through 3, wherein: at the time of
focus movement from an information recording layer onto another
information recording layer, the optical information storage medium
reproduction apparatus moves the focus from the information
recording layer onto the another information recording layer with
reproduction laser power being maintained to be lower than the
reproduction laser power for reading the information recording
layer farthest from the reproduction-laser-incident surface.
5. The optical information storage medium reproduction apparatus as
set forth in claim 4, wherein: the optical information storage
medium reproduction apparatus moves the focus from the information
recording layer onto the another information recording layer with
reproduction laser power for reading one of the information
recording layers that is closer to the reproduction-laser-incident
surface.
6. The optical information storage medium reproduction apparatus as
set forth in any one of claims 1 through 5, wherein: in a case
where the optical information storage medium includes 2 information
recording layers, the optical information storage medium
reproduction apparatus reproduces the optical information storage
medium in the order from one of the 2 information recording layers
that is closer to the reproduction-laser-incident surface than the
other one of the 2 information recording layers.
7. A control method for controlling an optical information storage
medium reproduction apparatus for reproducing an optical
information storage medium in which a plurality of information
recording layers are laminated, each of the plurality of
information recording layers including a recording mark having a
length shorter than an optical system resolution limit, said
control method comprising: setting, at the time of reading an
information recording layer closest to a
reproduction-laser-incident surface of the optical information
storage medium, reproduction laser power to be lower than
reproduction laser power for reading an information recording layer
farthest from the reproduction-laser-incident surface but not lower
than minimum reproduction laser power that satisfies a reproduction
signal characteristic that the optical information storage medium
reproduction apparatus requires.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. Ser.
No. 12/734,169, filed on Apr. 14, 2010 which is a national stage
application pursuant to 35 U.S.C. .sctn.371 of PCT application
PCT/JP2008/067327, filed Sep. 25, 2008, which claims the benefit of
Japanese Application No. 273204/2007, filed Oct. 19, 2007. The
entire contents of the aforementioned applications are hereby
incorporated herein by this reference.
TECHNICAL FIELD
[0002] The present invention relates to an optical information
storage medium reproduction apparatus for reproducing an optical
information storage medium by use of a super resolution
reproduction technique, and a control method of the optical
information storage medium reproduction apparatus.
BACKGROUND ART
[0003] In recent years, information technology, information
communication technology, and multimedia technology have been
greatly advanced. This increases demand for an increase in density
and capacity of an optical information storage medium.
[0004] To cope with such demand, there have been developed various
techniques, such as multilayer techniques for forming information
recording layers in a multilayered manner and super resolution
techniques using a reproduction layer that allows reading of a
recording mark shorter than a resolution limit of an optical
information storage medium reproduction apparatus.
[0005] Initially explained is one of the multilayer techniques. The
following describes a double-layer technique, which is most simple
among the multilayer techniques. As disclosed in Patent Literature
1, for example, a double-layer optical information storage medium
has such a structure that a first information recording layer and a
second information recording layer are provided in this order from
a side of a reproduction-laser-striking surface of the double-layer
optical information storage medium, and an intermediate layer is
provided therebetween so that the first and second information
recording layers are separated from each other. In this
arrangement, since the first recording layer is a translucent layer
that passes reproduction light therethrough, a reproduction laser
entering from the reproduction-layer-incident surface can be
focused onto either of the first and second information recording
layers so that information can be recorded in or read from the
either of the first and second information recording layers.
Accordingly, with the use of the double-layer technique, it is
possible to approximately double an information recording capacity
of the optical information storage medium, by simple
arithmetic.
[0006] For a structure of an optical information storage medium
having at least 3 information recording layers, it is also possible
to adopt, similarly to the above example of the double-layer
technique, such a structure that a first recording layer, a second
recording layer, a third recording layer, . . . , and an nth
recording layer are provided in this order from a side of a
reproduction-laser-incident surface of the optical information
storage medium, and an intermediate layer is sandwiched between two
of these information recording layers so as to separate them from
one another.
[0007] Further, the above optical information storage media do not
employ any super resolution techniques. Therefore, in the optical
information storage media, a shortest recording mark length in each
of the layers is longer than a resolution limit of an optical
information storage medium reproduction apparatus.
[0008] The following explains about the super resolution
techniques. The super resolution technique is a technique for read
a signal having a recording mark length shorter than an optical
resolution limit (hereinafter, referred to as optical diffraction
limit) in a reproduction optical system. More specifically, a light
spot diameter is represented by .lamda./NA substantially, where
.lamda. is a wavelength of light emitted from a light source and NA
is a numerical aperture of an objective lens for forming a light
spot.
[0009] That is, the super resolution technique is a technique for
recording/reading a recording mark having a recording mark length
equal to or less than this optical diffraction limit. Further,
reproduction of an optical information storage medium with the use
of the super resolution technique is referred to as super
resolution reproduction.
[0010] Further, it has been known that a length of a resolution
limit of a conventional optical information reproduction apparatus,
which does not use the super resolution technique, is around
.lamda./(4NA), which is one fourth of the light spot diameter. In
the following description, this limit is simply referred to as a
resolution limit. It should be noted that since the resolution
limit is actually affected by elements in an optical system in
addition to the theory, there might be some differences between an
actual value of the resolution limit and a theoretical value
obtained from the wavelength and the numerical aperture.
[0011] As described above, with the use of the super resolution
technique, it is possible to record/read a recording mark having a
recording mark length longer than the resolution limit. This can
improve an information recording capacity of the optical
information storage medium.
[0012] Patent Literature 2 proposes a super resolution optical
information storage medium that uses, as the super resolution
technique, a super resolution technique utilizing prepits each made
up in a form of a concavity or a convexity, which super resolution
technique contributes to reading of information called
Super-ROM.
[0013] This super resolution optical information storage medium has
not been clarified yet in detail in terms of a reproduction
mechanism. However, by using Mo, W, Si, Ge, and the like material
instead of Al and Au, which are conventionally used, to form a
reflection layer of a read-only disk, it is possible to read a
signal having a recording pit length shorter than the resolution
limit, which signal cannot be read by a conventional optical
system.
[0014] Further, a so-called multilayer super resolution technique,
which is a technique that combines the aforementioned multilayer
technique and super resolution technique, that is, a technique in
which the super resolution technique is applied to each information
recording layer in a multilayer optical information storage medium,
is expected as a technique that allows a further increase in the
information recording capacity. The multilayer super resolution
technique may adopt the aforementioned double-layer technique as
the multilayer technique. It is called a double-layer super
resolution technique.
Citation List
[0015] Patent Literature 1
[0016] Japanese Patent Application Publication, Tokukai, No.
2007-026503 A (Publication Date: Feb. 1, 2007)
[0017] Patent Literature 2
[0018] Japanese Patent Application Publication, Tokukai, No.
2001-250274 A (Publication Date: Sep. 14, 2001)
[0019] Patent Literature 3
[0020] Japanese Patent Application Publication, Tokukai, No.
2004-362718 A (Publication Date: Dec. 24, 2004)
[0021] Generally, the super resolution reproduction in the super
resolution techniques requires reproduction laser power higher than
power that is normally required. As one example of the super
resolution techniques, there is a mask-type super resolution
technique in which a so-called mask layer is provided on an
information recording layer.
[0022] There are two types as the mask-type super resolution
technique depending on characteristics, a heat-mode type and a
photon-mode type. In either case, formation of a mask region and an
aperture region requires a high temperature and a large amount of
light in a medium. This requires reproduction laser power higher
than power that is normally required. In addition, it has been also
reported that other super resolution techniques, such as the super
resolution technique disclosed in Patent Literature 2, require
reproduction laser power higher than power that is normally
required.
[0023] However, reading of an information recording layer with
inappropriately high reproduction laser power may damage recording
marks.
SUMMARY OF INVENTION
[0024] The present invention is accomplished in view of the above
problems. An object of the present invention is to provide (i) an
optical information storage medium reproduction apparatus by which
a multilayer super resolution optical information storage medium,
which is a high-density optical information storage medium, is
stably reproduced, and (ii) a control method of the optical
information storage medium reproduction apparatus.
[0025] In order to achieve the above object, an optical information
storage medium reproduction apparatus according to the present
invention is an optical information storage medium reproduction
apparatus for reproducing an optical information storage medium in
which a plurality of information recording layers are laminated,
each of the plurality of information recording layers including a
recording mark having a length shorter than an optical system
resolution limit, and the optical information storage medium
reproduction apparatus reads an information recording layer closest
to a reproduction-laser-incident surface of the optical information
storage medium, with reproduction laser power that is set to be
lower than reproduction laser power for reading an information
recording layer farthest from the reproduction-laser-incident
surface but not lower than minimum reproduction laser power that
satisfies a reproduction signal characteristic that the optical
information storage medium reproduction apparatus requires.
[0026] Further, in order to achieve the above object, an optical
information storage medium reproduction apparatus according to the
present invention is an optical information storage medium
reproduction apparatus for reproducing an optical information
storage medium in which a plurality of information recording layers
are laminated, each of the plurality of information recording
layers including a recording mark having a length not longer than
120 nm, which optical information storage medium reproduction
apparatus includes an optical system including a laser light source
capable of irradiating laser light having a wavelength of not less
than 400 nm but not more than 410 nm and an objective lens having a
numerical aperture of not less than 0.83 but not more than 0.87,
and the optical information storage medium reproduction apparatus
reads an information recording layer closest to a
reproduction-laser-incident surface of the optical information
storage medium, with reproduction laser power that is set to be
lower than reproduction laser power for reading an information
recording layer farthest from the reproduction-laser-incident
surface but not lower than minimum reproduction laser power that
satisfies a reproduction signal characteristic that the optical
information storage medium reproduction apparatus requires.
[0027] Further, in order to achieve the above object, a control
method according to the present invention is a control method for
controlling an information storage medium reproduction apparatus
for reproducing an optical information storage medium in which a
plurality of information recording layers are laminated, each of
the plurality of information recording layers including a recording
mark having a length shorter than an optical system resolution
limit, and the control method includes setting, at the time of
reading an information recording layer closest to a
reproduction-laser-incident surface of the optical information
storage medium, reproduction laser power to be lower than
reproduction laser power for reading an information recording layer
farthest from the reproduction-laser-incident surface but not lower
than minimum reproduction laser power that satisfies a reproduction
signal characteristic that the optical information storage medium
reproduction apparatus requires.
[0028] In the above arrangement, at the time of reading the
information recording layer closest to the
reproduction-laser-incident surface of the optical information
storage medium, the optical information storage medium reproduction
apparatus sets reproduction laser power to be lower than
reproduction laser power for reading the information recording
layer farthest from the reproduction-laser-incident surface but not
lower than minimum reproduction laser power that satisfies a
reproduction signal characteristic that the optical information
storage medium reproduction apparatus requires. Accordingly, the
optical information storage medium reproduction apparatus reads the
information recording layer closest to the
reproduction-laser-incident surface by irradiating the information
recoding layer with laser light having the reproduction laser power
thus set. As a result, with the above arrangement, it is possible
to prevent that the information recording layer closest to the
reproduction-laser-incident surface is read with inappropriately
high reproduction laser power, thereby making it possible to
prevent a decrease in reflectance and a deterioration in
reproduction signal characteristic along with repeat reproduction.
Consequently, it is possible to stably reproduce a multilayer super
resolution optical information storage medium like the above
optical information storage medium.
[0029] In a case where a conventional optical information storage
medium reproduction apparatus reproduces a multilayer information
storage medium including n (n is an integer not less than 2)
information recording layers, the same reproduction laser power is
employed to read a first information recording layer, which is
first from the reproduction-laser-incident surface, and an nth
information recording layer, which is nth from the
reproduction-laser-incident surface. For example, in a case where a
conventional double-layer optical information storage medium is
reproduced, a first information recording layer and a second
information recording layer are read with the same reproduction
laser power.
[0030] In view of this, the inventor(s) of the present invention
found the following fact. That is, in the case where the first
information recording layer and the second information recording
layer of the double-layer super resolution optical information
storage medium are read with the same reproduction laser power as
such, recording marks of the first information recording layer are
damaged, thereby resulting in that information stored in the first
information recording layer is rendered unreadable.
[0031] The above arrangement of the present invention is applicable
to an optical information storage medium reproduction apparatus
including an optical system constituted by (i) a laser light source
capable of irradiating laser light which is like a blue laser
employed by a Blu-ray Disc (registered trademark) reproduction
apparatus and which has a wavelength of not less than 400 nm but
not more than 410 nm, and (ii) an objective lens having a numerical
aperture of 0.85. It should be noted that even if the numerical
aperture has an error of around .+-.0.02, it hardly affects the
advantageous effects of the present invention. On this account, the
numerical aperture may be not less than 0.83 but not more than
0.87.
[0032] Furthermore, the above arrangement of the present invention
is also applicable to reading of information recording layers, such
as an information recording layer on which a plurality of recording
marks including a recording mark shorter than 120 nm have been
formed, and an information recording layer in which information is
to be recorded in the form of a plurality of recording marks
including a recording mark shorter than 120 nm.
[0033] The above optical information storage medium may be a
read-only optical information storage medium (read-only type) in
which information has been already recorded, or an optical
information storage medium (writable/readable type) in which a
piece of information has been recorded in a part of an information
recording layer and another piece of information may be
additionally recorded therein and in which the piece of information
has been recorded in at least one of a plurality of information
recording layers.
[0034] Additional objects, features, and strengths of the present
invention will be made clear by the description below. Further, the
advantages of the present invention will be evident from the
following explanation in reference to the drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0035] FIG. 1 shows one embodiment of the present invention and is
a block diagram schematically illustrating an arrangement of an
essential part of an optical information storage medium
reproduction apparatus.
[0036] FIG. 2 shows one embodiment of the present invention and is
a block diagram schematically showing an arrangement of an optical
information storage medium reproduction apparatus.
[0037] FIG. 3 is a cross-sectional view schematically illustrating
an exemplary double-layer optical information storage medium
according to the present invention.
[0038] FIG. 4 is a graph showing reproduction-laser-power
dependence of jitter of an optical information storage medium
reproduction apparatus of Reference Example 1 in the present
invention.
[0039] FIG. 5 is a graph showing reproduction-laser-power
dependence of bER measured at the time of reproducing a disk #1 of
the present invention and an optical information storage medium of
Comparative Example 1.
[0040] FIG. 6 is a graph showing reproduction-laser-power
dependence of CNR measured at the time of reproducing a disk #2 of
the present invention and an optical information storage medium of
Comparative Example 2.
[0041] FIG. 7 is a graph showing reproduction-time dependence of
normalized reflectance of a first information recording layer of an
optical information storage medium as the disk #1 of the present
invention.
REFERENCE SIGNS LIST
[0042] 10 Optical Information Storage Medium Reproduction
Apparatus
[0043] 12 Polarization Beam Splitter (Optical System)
[0044] 13 Laser Light Resource (Optical System)
[0045] 15 Detector (Optical System)
[0046] 19 Control Section
[0047] 21 Optical Pickup (Optical System)
[0048] 26 Power Control Section
[0049] 100 Optical Information Storage Medium
[0050] 100a Super Resolution Optical Information
[0051] Storage Medium
[0052] 100d Double-layer Super Resolution Optical Information
Storage Medium (Optical Information Storage Medium)
[0053] 100e Double-layer Super Resolution Optical Information
Storage Medium (Optical Information Storage Medium)
[0054] 101 Light-transmitting Layer
[0055] 102 First Information Recording Layer (Information Recording
Layer Closest to Reproduction-laser-incident Surface)
[0056] 103 Intermediate Layer
[0057] 104 Second Information Recording Layer (Information
Recording Layer Farthest from Reproduction-laser-incident
Surface)
[0058] 105 Substrate
DESCRIPTION OF EMBODIMENTS
[0059] One embodiment is described below with reference to FIG. 1
through FIG. 7.
[0060] (Optical Information Storage Medium Reproduction
Apparatus)
[0061] FIG. 2 is a block diagram schematically illustrating one
exemplary arrangement of an optical information storage medium
reproduction apparatus according to the present embodiment. An
optical information storage medium reproduction apparatus 10
illustrated in FIG. 2 can optically reproduce an optical
information storage medium 100. The optical information storage
medium 100 may be a double-layer super resolution optical
information storage medium 100a or a normal optical information
storage medium 100b other than the double-layer super resolution
optical information storage medium.
[0062] The present embodiment deals with, as an example, a case
where the double-layer super resolution optical information storage
medium 100a is reproduced as a multilayer super resolution optical
information storage medium that is reproduced by the optical
information storage medium reproduction apparatus 10. However, the
present embodiment is not limited to this, and a super resolution
optical information storage medium having at least 3 layers may be
reproduced by the optical information storage medium reproduction
apparatus 10. Further, the normal optical information storage
medium 100b that is reproduced by the optical information storage
medium reproduction apparatus 10 may be an optical information
storage medium having at least 2 information recording layers.
[0063] As illustrated in FIG. 2, the optical information storage
medium reproduction apparatus 10 includes a laser control circuit
14A, a signal processing circuit 14B, a head amplifier 16, an RF
amplifier 17A, a signal processing circuit 17B for RF signals, a
servo processing circuit 18, a control section 19, a spindle motor
20, an optical pickup 21, and an optical pickup motor 22. The
optical pickup 21 includes a polarization beam splitter 12, a laser
light source 13, and a detector 15.
[0064] In the optical information storage medium reproduction
apparatus 10, initially, the spindle motor 20 rotates the optical
information storage medium 100, and the control section 19 controls
the optical pickup motor 22 to move the optical pickup 21. Then,
the laser control circuit 14A causes the laser light source 13 to
emit reproduction laser light.
[0065] The signal processing circuit 14B is for generating a signal
for use in the laser control circuit 14A. For example, in a case
where the optical information storage medium reproduction apparatus
10 has a function of recording information in an optical
information storage medium, the signal processing circuit 14B
generates a recording signal so that the laser control circuit 14A
controls the laser light source 13 by use of the recording
signal.
[0066] The reproduction laser light passes through the polarization
beam splitter 12 and then strikes the optical information storage
medium 100. Reflection light reflected off the optical information
storage medium 100 returns to the polarization beam splitter 12 and
then reaches the detector 15 via the polarization beam splitter 12.
The optical pickup 21 includes an objective lens (not shown). A
laser wavelength and a numerical aperture for use in a Blue-ray
Disc (registered trademark) reproduction apparatus may be used,
respectively, as a laser wavelength of laser light emitted from the
laser light source 13 and as a numerical aperture of the objective
lens. In this case, the laser wavelength is substantially 405 nm,
and the numerical aperture is substantially 0.85.
[0067] The detector 15 outputs an electrical signal based on the
received reflection light. The electrical signal is fed to the head
amplifier 16 so as to be amplified. The electrical signal thus
amplified is then fed to the servo processing circuit 18 so as to
cause the servo processing circuit 18 to perform various servo
controls. Further, the electrical signal is fed to the RF amplifier
17A so as to be amplified further, and then fed to the signal
processing circuit 17B. The electrical signal is then fed to the
control section 19 via the signal processing circuit 17B.
[0068] (Control Section of Optical Information Storage Medium
Reproduction Apparatus)
[0069] By referring to FIG. 1, the following describes the control
section 19 of the optical information storage medium reproduction
apparatus 10, more specifically. FIG. 1 is a block diagram
illustrating an essential part of the control section 19. As
illustrated in FIG. 1, the control section 19 includes an access
position control section 23, a signal processing section 24, a
medium identifying section 25, a power control section 26, and a
reproduction clock control section 27.
[0070] The access position control section 23 controls the optical
pickup motor 22 so that the optical pickup 21 can make access to a
desired position on the optical information storage medium 100.
[0071] The signal processing section 24 processes a medium
identification signal fed from the head amplifier 16, and then
supplies the medium identification signal to the medium identifying
section 25. The medium identifying section 25 identifies whether or
not the optical information storage medium 100 is a double-layer
super resolution optical information storage medium 100a, based on
the medium identification signal supplied from the signal
processing section 24.
[0072] When the optical information storage medium 100 is
identified as the double-layer super resolution optical information
storage medium 100a, based on a result of the identification by the
medium identifying section 25, the power control section 26
controls the laser control circuit 14A so as to set reproduction
laser power. More specifically, for reading of a first information
recording layer, reproduction laser power Pr1 for the first
information recording layer is set. For reading of a second
information recording layer, reproduction laser power Pr2 for the
second information recording layer is set. The reproduction laser
power Pr1 for the first information recording layer and the
reproduction laser power Pr2 for the second information recording
layer will be described later more specifically.
[0073] The reproduction clock control section 27 switches a
reproduction clock for use in the signal processing circuit 17B,
between a reproduction clock suitable for a normal optical
information storage medium 100b and a reproduction clock suitable
for a super resolution optical information storage medium 100a,
based on the result of the identification of the optical
information storage medium 100 by the medium identifying section
25.
[0074] The following explains about the super resolution optical
information storage medium 100a with reference to FIG. 3. FIG. 3 is
a cross-sectional view schematically illustrating a double-layer
information storage medium. In this explanation, assume that the
super resolution optical information storage medium 100a is a
double-layer super resolution optical information storage medium,
for example. The super resolution optical information storage
medium 100a includes a light-transmitting layer 101a, a first
information recording layer 102a, an intermediate layer 103a, a
second information recording layer 104a, and a substrate 105a.
[0075] The optical information storage medium reproduction
apparatus 10 reads information stored in the optical information
storage medium 100 by use of a reproduction clock received from the
reproduction clock control section 27 and an electrical signal
received from the RF amplifier 17A via the signal processing
circuit 17B.
[0076] Further, the following describes which information recording
layer is to be focused, the first information recording layer 102a
or the second information recording layer 104a, in a case where the
super resolution optical information storage medium 100a is
reproduced. When a focus search process is performed by moving the
objective lens (not shown) of the optical pickup 21 in order from a
position away from the super resolution optical information storage
medium 100a toward a focus direction, a focus error signal for use
in the servo processing circuit 18 exhibits an S-shaped
characteristic every time the focus error signal passes through
each of the information recording layers. At this time, it is
counted how many times the S-shaped characteristic is exhibited,
and the optical pickup 21 is controlled in accordance with the
counted number so as to select either the first information
recording layer 102a or the second information recording layer
104a, accordingly.
[0077] (How to Identify Optical Information Storage Medium)
[0078] Next will be explained how to identify whether an optical
information storage medium 100 to be reproduced by the optical
information storage medium reproduction apparatus 10 is a
double-layer super resolution optical information storage medium
100a or not.
[0079] One of the methods is such that medium information
indicative of whether or not the optical information storage medium
100 is a double-layer super resolution optical information storage
medium 100a is added to the optical information storage medium 100
in a predetermined manner.
[0080] More specifically, medium information indicating that an
optical information storage medium to be reproduced is the
double-layer super resolution optical information storage medium
100a is stored in the double-layer super resolution optical
information storage medium 100a in the form of recording marks
having a recording mark length not shorter than a resolution limit
of the optical information storage medium reproduction apparatus
10. The medium information is read with low reproduction laser
power used for the normal optical information storage medium 100b.
Herewith, it is possible to judge whether or not the optical
information storage medium 100 is a double-layer super resolution
optical information storage medium 100a, based on the medium
information.
[0081] With the arrangement, it is possible to prevent such a
problem that the first information recording layer or the second
information recording layer is focused with high reproduction laser
power accidentally and thereby rendered unreadable irreversibly.
Furthermore, the medium information may be recorded in a form of a
barcode indicative of the medium information in the vicinity of an
internal opening of the optical information storage medium 100.
[0082] Alternatively, medium determination means for judging medium
information may be used before the spindle motor 20 rotates the
optical information storage medium 100. For example, the medium
information is mechanically identified according to a part of the
optical information storage medium 100, a cutout of a part of a
cartridge housing the optical information storage medium 100, or
the like.
[0083] In a case where it is judged, in accordance with the medium
information and any of the above methods, that the optical
information storage medium 100 is the double-layer super resolution
optical information storage medium 100a, the optical information
storage medium reproduction apparatus 10 performs the reproduction
with reproduction laser power for the double-layer super resolution
optical information storage medium 100a. At this time, the optical
information storage medium reproduction apparatus 10 reads out
other information (i.e., address information and the
after-mentioned minimum reproduction laser power Pr1min for the
first information recording layer) related to the super resolution
optical information storage medium. The other information related
to the super resolution optical information storage medium can be
read even when the other information is recorded in the form of
patterns including a pattern having a recording mark length not
longer than the resolution limit of the optical information storage
medium reproduction apparatus 10. This makes it possible to
increase density of information including the other information
related to the super resolution optical information storage medium.
Moreover, the medium determination means may be able to judge
information on the after-mentioned reproduction laser power Pr1 for
the first information recording layer and the after-mentioned
reproduction laser power Pr2 for the second information recording
layer.
[0084] In this case, it is preferable that the playback of the
double-layer super resolution optical information storage medium
start from the first information recording layer. This can prevent
such a problem that the first information recording layer is
accidentally read with the reproduction laser power Pr2 for the
second information recording layer, which is high reproduction
laser power, at the start of the reproduction and thereby the first
information recording layer is rendered unreadable
irreversibly.
[0085] It should be noted that, to start the reproduction in the
order from the first information recording layer is preferable only
in the case of the double-layer super resolution optical
information storage medium. This is not true for an n-layer super
resolution optical information storage medium in which n is at
least 3.
Examples
[0086] (Optical Information Storage Medium)
[0087] The following deals with a super resolution optical
information storage medium 100a and a normal optical information
storage medium 100b, which are reproduced by the optical
information storage medium reproduction apparatus 10 according to
the present embodiment.
[0088] One example of a conventional double-layer optical
information storage medium is a double-layer optical information
storage medium 100c of Reference Example 1, having a structure
illustrated in FIG. 3.
Reference Example 1
[0089] The following describes, with reference to FIG. 3, a case
where a conventional optical information storage medium
reproduction apparatus plays a conventional double-layer optical
information storage medium. As one exemplary case where the optical
information storage medium reproduction apparatus plays such an
optical information storage medium, Reference Example 1 deals with
a case where the double-layer optical information storage medium
100c, which is a conventional optical information storage medium
including 2 information recording layers, is reproduced. As
illustrate in FIG. 3, the double-layer optical information storage
medium 100c includes a light-transmitting layer 101c, a first
information recording layer 102c, an intermediate layer 103c, a
second information recording layer 104c, and a substrate 105, which
are laminated in this order from a reproduction-laser-incident
surface.
[0090] The light-transmitting layer 101c is formed of a transparent
resin layer (film thickness: 75 .mu.m), the first information
recording layer 102c is formed of a translucent reflection film
(Au, film thickness: 15 nm), the intermediate layer 103c is formed
of a transparent ultraviolet-curing resin layer (film thickness: 25
.mu.m), the second information recording layer 104c is formed of a
reflection film (Au, film thickness: 50 nm), and the substrate 105c
is formed of a resin substrate.
[0091] On the intermediate layer 103c and the substrate 105c of the
double-layer optical information storage medium 100c to be
reproduced by the optical information storage medium reproduction
apparatus of Reference Example 1, prepits (not shown) are formed
each in the form of a concavity and/or a convexity. By laminating
the translucent reflection film and the reflection film on the
prepits of the intermediate layer 103c and the substrate 105c,
respectively, the concavities/convexities are transferred onto the
translucent reflection film and the reflection film. Consequently,
the prepits are formed as recording marks on the first information
recording layer 102c and the second information recording layer
104c.
[0092] That is, the double-layer optical information storage medium
100c is a so-called read-only optical information storage medium.
Further, the prepits, that is, the recording marks, of the
double-layer optical information storage medium 100c of Reference
Example 1 are formed in a form of recording patterns based on a
1-7PP modulation method adopted by Blu-ray Disc (registered
trademark), in which 2T mark length, which is a shortest recording
mark length, is 149 nm. Here, T indicates a time equivalent to one
period of a clock.
[0093] Reproduction-laser-power dependence of jitter of each of the
first information recording layer 102c and the second information
recording layer 104c in the double-layer optical information
storage medium 100c of Reference Example 1 is measured by use of a
disk measurement device which includes a semiconductor laser that
irradiates light having a wavelength of 405 nm, which is a
wavelength of blue laser light, and an optical system including a
numerical aperture NA of 0.85. The result of the measurement is
shown in FIG. 4.
[0094] The jitter is an index indicative of fluctuation in
reproduction signal in a time axis direction. As a value of the
jitter becomes smaller, the jitter indicates a better reproduction
signal characteristic. Generally, the jitter is often used to show
a reproduction signal characteristic of a medium.
[0095] Further, a threshold 30 shown by a bold dotted line in FIG.
4 is a threshold of a jitter value at which, in general, the
optical information storage medium reproduction apparatus can
stably read information stored in the optical information storage
medium 100, i.e., a threshold of the jitter necessary for the
optical information storage medium reproduction apparatus to stably
reproduce the optical information storage medium 100.
[0096] As shown in FIG. 4, respective jitters of the first
information recording layer 102c and the second information
recording layer 104c in the double-layer optical information
storage medium 100c are not dependent on reproduction laser power,
and are substantially constant and not more than the threshold 30.
The reproduction laser power of the optical information storage
medium reproduction apparatus may take any value as long as the
reproduction laser power causes the jitter value to be not more
than the threshold 30. On this account, the double-layer optical
information storage medium 100c exhibiting such a reproduction
signal characteristic shown in Reference Example 1 can select, from
among a wide range of laser power, respective values for
reproduction laser power for the first information recording layer
102c and reproduction laser power for the second information
recording layer 104c.
[0097] (Reproduction Laser Power in Conventional Optical
Information Storage Medium Reproduction Apparatus)
[0098] In the conventional optical information storage medium
reproduction apparatus, reproduction laser power for reading the
first information recording layer 102c and reproduction laser power
for reading the second information recording layer 104c are set to
the same value. For example, in FIG. 4, a value of 0.7 mW or the
like value can be employed as the reproduction laser power for each
of the first information recording layer 102c and the second
information recording layer 104c.
[0099] One of the reasons for this is as below. If the reproduction
laser power for reading the first information recording layer 102c
and the reproduction laser power for reading the second information
recording layer 104c are set to values different from each other,
control of the reproduction laser power by APC (automatic power
control) or the like becomes complicated, and it becomes difficult
for the optical information storage medium reproduction apparatus
to read the first information recording layer 102c and the second
information recording layer 104c at the same reproduction
circuit.
[0100] For this reason, in the conventional optical information
storage medium reproduction apparatus for reproducing the
double-layer optical information storage medium 100c, the
reproduction laser power for reading the first information
recording layer and the reproduction laser power for reading the
second information recording layer are set to the same value.
[0101] The inventor(s) of the present invention evaluated the
reproduction signal characteristic according to the difference in
laser power on the basis of indices, such as CNR, jitter, and bER,
by use of a multilayer super resolution optical information storage
medium, and found the following fact. That is, reading of a first
information recording layer of the multilayer super resolution
optical information storage medium with reproduction laser power
equivalent to that for reading a second information recording layer
thereof damages the first information recording layer, similarly to
the conventional and practical optical information storage medium
reproduction apparatus for reproducing a double-layer optical
information storage medium.
[0102] [Double-layer Super Resolution Optical Information Storage
Medium]
[0103] The multilayer super resolution optical information storage
medium will be explained below more specifically, by taking, as one
example, a disk #1 and a disk #2, each of which is a double-layer
super resolution optical information storage medium. Structures of
the disks #1 and #2 are explained with reference to the structure
of FIG. 3, similarly to Reference Example 1.
[0104] [Disk #1]
[0105] A double-layer super resolution optical information storage
medium 100d as the disk #1 includes a light-transmitting layer
101d, a first information recording layer 102d, an intermediate
layer 103d, a second information recording layer 104d, and a
substrate 105d, which are laminated in this order from a
reproduction-laser-incident surface.
[0106] The light-transmitting layer 101d is formed of a transparent
resin layer (film thickness: 75 .mu.m), the first information
recording layer 102d is formed of a temperature-sensitive layer
(zinc oxide, film thickness: 60 nm) and a light-absorbing layer
(Ta, film thickness: 7.5 nm), the intermediate layer 103d is formed
of a transparent ultraviolet-curing resin layer (film thickness: 25
.mu.m), the second information recording layer 104d is formed of a
temperature-sensitive layer (zinc oxide, film thickness: 60 nm) and
a light-absorbing layer (Ta, film thickness: 15 nm), and the
substrate 105d is formed of a resin substrate. A super resolution
technique adopted by the double-layer super resolution optical
information storage medium 100d is based on the technique disclosed
in Patent Literature 3.
[0107] [Disk #2]
[0108] A double-layer super resolution optical information storage
medium 100e as the disk #2 includes a light-transmitting layer
101e, a first information recording layer 102e, an intermediate
layer 103e, a second information recording layer 104e, and a
substrate 105e, which are laminated in this order from a
reproduction-laser-incident surface.
[0109] The light-transmitting layer 101e is formed of a transparent
resin layer (film thickness: 75 .mu.m), the first information
recording layer 102e is formed of a functional layer (Si, film
thickness: 5 nm), the intermediate layer 103e is formed of a
transparent ultraviolet-curing resin layer (film thickness: 25
.mu.m), the second information recording layer 104e is formed of a
functional layer (Si, film thickness: 50 nm), and the substrate
105e is formed of a resin substrate. A super resolution technique
adopted by the double-layer super resolution optical information
storage medium 100e is the technique disclosed in Patent Literature
2.
[0110] Comparative Examples 1 and 2
[0111] Optical information storage media each having the following
properties were reproduced by the optical information storage
medium reproduction apparatus 10, for comparison. A result of the
reproduction is described as below. The optical information storage
media reproduced here are optical information storage media that
can be reproduced without any of the super resolution techniques,
and were reproduced just for comparison to prove that the
double-layer super resolution optical information storage media
100d and 100e have a super resolution characteristic. The optical
information storage media reproduced in Comparative Examples 1 and
2 each include a light-transmitting layer, an information recording
layer, and a substrate, which are laminated in this order from a
reproduction-laser-incident surface.
[0112] The light-transmitting layer is formed of a transparent
resin layer (film thickness: 100 .mu.m), the information recording
layer is formed of a reflection film (Au, film thickness: 50 nm for
Comparative Example 1, 20 nm for Comparative Example 2), and the
substrate is formed of a resin substrate.
[0113] On each of the intermediate layer 103d and the substrate
105d of the double-layer super resolution optical information
storage medium 100d as the disk #1, each of the intermediate layer
103e and the substrate 105e of the double-layer super resolution
optical information storage medium 100e as the disk #2, and each of
the substrates of Comparative Examples 1 and 2, prepits each made
up in the form of a concavity and/or a convexity are formed.
[0114] For the disk #1, the temperature-sensitive layer and the
light-absorbing layer are laminated on the prepits, thereby
transferring the concavities/convexities to the light-absorbing
layer. Thus, the prepits are formed on the light-absorbing layer as
recording marks.
[0115] Similarly, for the disk #2, the functional layer is
laminated on the prepits, thereby transferring the
concavities/convexities to the functional layer. Thus, the prepits
are formed on the functional layer as recording marks. Further, for
Comparative Examples 1 and 2, the reflection film is laminated on
the prepits, thereby transferring the concavities/convexities on
the reflection film. Thus, the prepits are formed on the reflection
film as recording marks.
[0116] In view of this, the double-layer super resolution optical
information storage medium 100d, the optical information storage
medium in Comparative Example 1, the double-layer super resolution
optical information storage medium 100e, and the optical
information storage medium in Comparative Example 2 are a so-called
read-only optical information storage medium.
[0117] The prepits, i.e., the recording marks on the double-layer
super resolution optical information storage medium 100d and the
optical information storage medium in Comparative Example 1 are
formed in a recording pattern based on the 1-7PP modulation method
adopted by the Blu-ray Disc (registered trademark). A 2T mark
length, which is the shortest recording mark length, is 93 nm. The
1-7PP modulation method is called a random pattern method in which
a plurality of recording marks having different lengths are aligned
in a signal-reading direction in a regular manner according to a
predetermined method.
[0118] The prepits, i.e., the recording marks on the double-layer
super resolution optical information storage medium 100e and the
optical information storage medium of Comparative Example 2 are
formed in a single-frequency repeating pattern in which a recording
mark length is 100 nm. The single-frequency repeating pattern
method is called a monotone pattern method in which a mark space
ratio is 1:1.
[0119] (Measurement of Reproduction Signal Characteristic)
[0120] A reproduction signal characteristic of each of the
double-layer super resolution optical information storage media
100d and 100e, and the normal optical information storage media in
Comparative Examples 1 and 2 was measured by use of a disk
measurement device at the time of reproducing these media. Results
of the measurement are as follows.
[0121] (Measurement of Disk #1)
[0122] FIG. 5 is a graph showing reproduction-laser-power
dependence of bER (bit Error Rate) measured at the time of reading
of (i) the first information recording layer 102d, (ii) the second
information recording layer 104d, each in the double-layer super
resolution optical information storage medium 100d as the disk #1,
and (iii) the information recording layer in the normal optical
information storage medium of Comparative Example 1. The
measurement was carried out with the use of a disk measurement
device which includes a semiconductor laser that irradiates light
having a wavelength of 405 nm, which is a wavelength of blue laser
light, and an optical system having a numerical aperture NA of
0.85.
[0123] The optical system is the same as one for use in a Blu-ray
Disc (registered trademark) reproduction apparatus. As described
above, the resolution limit is represented by .lamda./(4NA).
Accordingly, a resolution limit of the disk measurement device is
about 120 nm. On this account, the shortest recording mark length,
93 nm, of the double-layer super resolution optical information
storage medium 100d and the optical information storage medium of
Comparative Example 1 is not longer than the resolution limit of
the optical system of the disk measurement device.
[0124] Moreover, the bER indicates a bit error ratio of a
reproduction signal. This is one of indices that represent the
reproduction signal characteristic of a medium. As a value of the
bER is smaller, the reproduction signal characteristic becomes
better.
[0125] When the shortest recording mark length is not longer than
the resolution limit, a value of jitter, which is generally used as
the index that represents the reproduction signal characteristic,
worsens markedly. As a result, the jitter cannot serve as the
index. In this case, it is difficult to evaluate the reproduction
signal characteristic based on the value of the jitter.
[0126] When the jitter takes a moderate value, the bER takes an
adequate value. However, in some cases, even if the jitter does not
take a moderate value, the bER still may take an adequate value.
The bER is an evaluation index value eventually necessary for a
practical optical information storage medium reproduction
apparatus. If the bER is adequate, a system itself works out. For
this reason, the bER was also used in this measurement as one of
the indices that represent the reproduction signal characteristic
of a medium.
[0127] A threshold 40 shown by a bold dotted line in FIG. 5 is a
threshold of the bER at which, in general, an optical information
storage medium reproduction apparatus can stably read information
recorded in an optical information storage medium. In other words,
the threshold 40 is a threshold of the reproduction signal
characteristic that a general optical information storage medium
reproduction apparatus requires. As shown in FIG. 5, respective
values of the bER that were measured at the time of the reading of
the first information recording layer 102d and the second
information recording layer 104d in the double-layer super
resolution optical information storage medium 100d are sufficiently
smaller than the value of the bER that is measured at the time of
the reading of the information recording layer in the optical
information storage medium in Comparative Example 1.
[0128] Further, as apparent from FIG. 5, respective ranges of
reproduction laser power that cause the respective values of the
bER, measured at the time of the reading of the first information
recording layer 102d and the second information recording layer
104d in the double-layer super resolution optical information
storage medium 100d, to be not more than the threshold 40 are
different from each other. More specifically, for the first
information recording layer 102d, the range of reproduction laser
power is from 1.0 mW to 3.7 mW, and for the second information
recording layer 104d, the range of reproduction laser power is 2.7
mW to 5.0 mW.
[0129] From the measurement results, it is demonstrated that the
range of reproduction laser power of the first information
recording layer 102d is lower than that of the second information
recording layer 104d. Moreover, it is also demonstrated that, on an
axis of the reproduction laser power, the range of reproduction
laser power of the first information recording layer 102d is placed
on a side where the reproduction laser power is relatively small,
as compared to the second information recording layer 104d.
[0130] In the double-layer super resolution optical information
storage medium, the second information recording layer 104d is read
definitely with reproduction light that passes through the first
information recording layer 102d. Therefore, an amount of the laser
light that reaches the second information recording layer 104d is
reduced. For this reason, reproduction laser power necessary for
reading the second information recording layer 104d should be
higher than that necessary for the first information recording
layer 102d.
[0131] Further, similarly to the conventional optical information
storage medium reproduction apparatus, there exists a value (for
example, 2.8 mW in FIG. 5) of the reproduction laser power that
allows respective values of the bER of the first information
recording layer 102d and the second information recording layer
104d to be not more than the threshold 40.
[0132] (Measurement of Disk #2)
[0133] FIG. 6 is graphs showing reproduction-laser-power dependence
of CNR (Carrier to Noise Ratio) measured at the time of reading (i)
the first information recording layer 102e, (ii) the second
information recording layer 104e, each in the double-layer super
resolution optical information storage medium 100e as the disk #2,
and (iii) the information recording layer in the optical
information storage medium of Comparative Example 2. The
measurement was carried out with the use of the same disk
measurement device as the one used for the measurement of the
double-layer super resolution optical information storage medium
100d, i.e., the disk measurement device which includes a
semiconductor laser that irradiates light having a wavelength of
405 nm, which is a wavelength of blue laser light, and an optical
system having a numerical aperture NA of 0.85.
[0134] As has been already described, the resolution limit is
represented by .lamda./(4NA). Accordingly, a resolution limit of
the disk measurement device is around 120 nm. On this account, the
recording mark length, 100 nm, of the double-layer super resolution
optical information storage medium 100e and the optical information
storage medium of Comparative Example 2 is not longer than the
resolution limit of the disk measurement device.
[0135] The CNR is one of evaluation indices for a single-frequency
repeating signal in a case where the recording marks are formed by
the monotone method, and is one of the indices representing the
reproduction signal characteristic of a medium. As a value of the
CNR becomes larger, the reproduction signal characteristic becomes
better.
[0136] As the evaluation index for a single-frequency repeating
signal, not the jitter nor the bER, but the CNR is generally used.
For this reason, in this measurement, the CNR was employed as the
index representing the reproduction signal characteristic of a
medium.
[0137] A threshold 50 shown by a bold dotted line in FIG. 6 is a
threshold of the CNR at which, in general, an optical information
storage medium reproduction apparatus can stably read information
stored in an optical information storage medium. That is, the
threshold 50 is a threshold of the reproduction signal
characteristic that a general optical information storage medium
reproduction apparatus requires.
[0138] As shown in FIG. 6, respective values of the CNR of the
first information recording layer 102e and the second information
recording layer 104e in the double-layer super resolution optical
information storage medium 100e are sufficiently larger than that
of the information recording layer of the optical information
storage medium of Comparative Example 2.
[0139] Further, as apparent from FIG. 6, respective ranges of
reproduction laser power that cause the respective values of the
CNR of the first information recording layer 102e and the second
information recording layer 104e in the double-layer super
resolution optical information storage medium 100e to be not less
than the threshold 50 are different from each other. More
specifically, for the first information recording layer 102e, the
range of reproduction laser power is 0.6 mW to 1.2 mW, and for the
second information recording layer 104e, the range of reproduction
laser power is not less than 1.1 mW.
[0140] From the measurement results, the inventor(s) of the present
invention found that, in the double-layer super resolution optical
information storage medium 100e, the range of reproduction laser
power of the first information recording layer 102e is lower than
that of the second information recording layer 104e. Moreover, it
is also found out that, on an axis of the reproduction laser power,
the range of reproduction laser power of the first information
recording layer 102e is placed on a side where the reproduction
laser power is relatively small, as compared to the second
information recording layer 104e.
[0141] Further, similarly to the conventional optical information
storage medium reproduction apparatus, there exists a value (for
example, 1.1 mW in FIG. 6) of the reproduction laser power that
allows respective values of the CNR of the first information
recording layer 102e and the second information recording layer
104e to be not less than the threshold 50.
[0142] Further, the inventor(s) of the present invention also found
the following fact. That is, similarly to the conventional optical
information storage medium reproduction apparatus, if the first
information recording layer 102d and the second information
recording layer 104d in the double-layer super resolution optical
information storage medium 100d are read with the same reproduction
laser power, the first information recording layer 102d is damaged
during the reading, thereby causing such a problem that information
stored in the first information recording layer 102e is rendered
unreadable. This problem also happens to the double-layer super
resolution optical information storage medium 100e.
[0143] For the double-layer super resolution optical information
storage medium 100d, the same reproduction laser power means, for
example, 3.0 mW, at which the respective values of the bER of the
first information recording layer 102d and the second information
recording layer 104d during the reproduction are not more than the
threshold. For the double-layer super resolution optical
information storage medium 100e, the same reproduction laser power
means, for example, 1.1 mW, at which the respective values of the
CNR of the first information recording layer 102e and the second
information recording layer 104e are not less than the
threshold.
[0144] (Number of Reproduction Times)
[0145] FIG. 7 is a graph showing a correlation between the number
of reproduction times and normalized reflectance at the time when
the first information recording layer 102d of the double-layer
super resolution optical information storage medium 100d is read
with predetermined reproduction laser power. FIG. 7 shows
reproduction-time dependence of normalized reflectance of a maximum
return-light amount of a reproduction signal, measured at the time
when the first information recording layer 102d of the double-layer
super resolution optical information storage medium 100d is read
with reproduction laser power of 1.2 mW, 1.6 mW, 2.0 mW, and 2.8
mW. The normalized reflectance indicates reflectance obtained by
normalizing reflectance at a certain number of reproduction times,
based on reflectance at the time when the reproduction is performed
once. For example, when the number of reproduction times is 1, the
normalized reflectance is 1.0.
[0146] As apparent from FIG. 7, as the reproduction laser power
increases, an amount of change in the normalized reflectance
increases along with an increase in the number of reproduction
times. This means that the characteristic becomes worse. For
example, in a case where the reproduction laser power is 2.8 mW and
the reproduction is performed 2000 times, an occurrence ratio of
the change in reflectance increases to at least 50%.
[0147] Generally, for the reproduction of an optical information
storage medium, there may be such a case where an optical pickup
temporarily stops on a certain track of the optical information
storage medium due to a pause until the next reproduction command
is inputted. Therefore, in order that stable reproduction is
realized, the optical information storage medium should have
reproduction resistance that allows the optical information storage
medium to be reproduced at least 2000 times.
[0148] Further, a large change in reflectance may cause poor focus.
Furthermore, the large change in reflectance may cause reproduction
signal amplitude to exceed its necessary range for reading
information stored in the optical information storage medium,
thereby making it difficult to read the information. In view of
this, in order that the optical information storage medium is
stably reproduced, it is necessary to restrain the occurrence ratio
of the change in reflectance to 10% to 20%, in general.
[0149] In the case where the first information recording layer 102d
of the double-layer super resolution optical information storage
medium 100d is read 2000 times with reproduction laser power of 2.8
mW, the necessary reproduction resistance and the change
characteristic in reflectance are not satisfied. For this reason,
it is substantially impossible to employ the reproduction laser
power of 2.8 mW for the reproduction of the double-layer super
resolution optical information storage medium 100d.
[0150] Further, it is also demonstrated, in the measurement
results, that in a case where the first information recording layer
102d of the double-layer super resolution optical information
storage medium 100d is read with reproduction laser power of not
more than 2.0 mW, the bER does not exceed its threshold even after
the reproduction is performed 2000 times. On the other hand, it is
demonstrated that in the case where the reproduction is performed
2000 times with reproduction laser power of 2.8 mW, the value of
the bER significantly increases and exceeds the threshold
irreversibly. That is, as the reproduction laser power increases,
the bER becomes worse along with an increase in the number of
reproduction times. From the viewpoint of the bER characteristic,
it is substantially impossible to employ the reproduction laser
power of 2.8 mW for the reading of the first information recording
layer 102d of the double-layer super resolution optical information
storage medium 100d.
[0151] Meanwhile, the second information recording layer 104d is
read definitely with a reproduction laser that has passed through
the first information recording layer 102d. That is, at the time
when an irradiated reproduction laser reaches the second
information recording layer 104d, the reproduction laser power of
the irradiated reproduction laser has decreased. On this account,
even in a case where the reproduction laser power is set to 2.8 mW,
at the time when the reproduction laser reaches the second
information recording layer 104d, the reproduction laser power is
less than 2.8 mW. This allows the reflectance and the bER of the
second information recording layer 104d to be stable.
[0152] For this reason, unlike the conventional optical information
storage medium reproduction apparatus, it is practically difficult
to read, with the same reproduction power, the first information
recording layer 102d and the second information recording layer
104d of the double-layer super resolution optical information
storage medium 100d.
[0153] Furthermore, similarly to the double-layer super resolution
optical information storage medium 100d, it is demonstrated that in
a case where the first information recording layer 102e of the
double-layer super resolution optical information storage medium
100e is read with reproduction laser power of 1.1 mW, the
reflectance decreases as the number of reproduction times
increases, thereby decreasing a characteristic of the first
information recording layer 102e. This ultimately causes the first
information recording layer 102e to be unreadable.
[0154] For this reason, unlike the conventional optical information
storage medium reproduction apparatus, it is practically difficult
to read, with the same reproduction power, the first information
recording layer 102e and the second information recording layer
104e of the double-layer super resolution optical information
storage medium 100e as the disk #2.
[0155] As described in the above [Background Art], the super
resolution techniques generally require high reproduction laser
power. Further, the second information recording layer 104e is read
definitely with reproduction light that has passed the first
information recording layer 102e. Therefore, an amount of laser
light that actually reaches the second information recording layer
104e has decreased. As a result, conditions of a necessary
temperature and light amount necessary for super resolution
reproduction are not satisfied. That is, the super resolution
reproduction of the second information recording layer 104e
requires reproduction laser power higher than power necessary for
the first information recording layer 102e.
[0156] (Reproduction Laser Power for Reading First Information
Recording Layer)
[0157] The following describes reproduction laser power at the time
when the optical information storage medium reproduction apparatus
10 reproduces a multilayer super resolution optical information
storage medium in which n pieces of information recording layers
are laminated. An information recording layer that is nth from a
reproduction-laser-incident surface side of the multilayer super
resolution optical information storage medium is referred to as the
nth information recording layer. The reproduction laser power
explained below is reproduction laser power Pr1 for the first
information recording layer and reproduction laser power Prn for
the nth information recording layer. That is, the following deals
with, as an example, a case where the double-layer super resolution
optical information storage medium 100d is reproduced. More
specifically, the following describes reproduction laser power Pr2
for a second information recording layer where n=2.
[0158] The reproduction laser power Pr1 for the first information
recording layer is reproduction laser power that is set when the
optical information storage medium reproduction apparatus 10 reads
the first information recording layer 102d. Further, the
reproduction laser power Pr2 for the second information recording
layer is reproduction laser power that is set when the optical
information storage medium reproduction apparatus 10 reads the
second information recording layer 104d.
[0159] Here, minimum reproduction laser power that satisfies a
reproduction signal characteristic that the optical information
storage medium reproduction apparatus 10 requires at the time of
the reading of the first information recording layer 102d is
referred to as minimum reproduction laser power Pr1 min for the
first information recording layer. For example, in FIG. 5,
reproduction laser power that causes bER measured at the time of
the reading of the first information recording layer 102d to be not
more than the threshold 40 is in a range from 1.0 mW to 3.7 mW.
That is, the minimum reproduction laser power Pr1min for the first
information recording layer can be set to 1.0 mW.
[0160] The reproduction laser power Pr2 for the second information
recording layer may be set to any value within a reproduction laser
power range which satisfies the reproduction signal characteristic
that the optical information storage medium reproduction apparatus
10 requires at the time of the reading of the second information
recording layer 104d. For example, in FIG. 5, reproduction laser
power that causes bER measured at the time of the reading of the
second information recording layer 104d to be not more than the
threshold 40 is in a range from 2.7 mW to 5.0 mW. The reproduction
laser power Pr2 for the second information recording layer can be
set to any value within the range.
[0161] It should be noted that, the lower a value of the
reproduction laser power Pr2 for the second information recording
layer is within the aforementioned laser power range, the more the
power consumption of the laser can be restrained. On this account,
as shown in FIG. 5, in a case of a reproduction signal
characteristic that is obtained at the time when the reproduction
laser power that causes the bER measured at the time of the reading
of the second information recording layer 104d to be not more than
the threshold 40 is within the range of 2.7 mW to 5.0 mW, it is
preferable to set the reproduction laser power Pr2 for the second
information recording layer to 2.7 mW.
[0162] How to determine the reproduction laser power Pr2 for the
second information recording layer is not especially limited in any
manner. For example, before the reproduction of the double-layer
super resolution optical information storage medium 100d starts,
the reproduction laser power Pr2 for the second information
recording layer may be set with the use of means for identifying
information related to settings of the reproduction laser power Pr2
for the second information recording layer. The above means
identifies the information before the spindle motor 20 rotates the
optical information storage medium 100 (for example, in such a
manner that a cutout or the like formed in a part of a disk or a
part of a cartridge housing the disk, is recognized
mechanically).
[0163] Further, in a case where the information related to the
settings of the reproduction laser power Pr2 for the second
information recording layer is recorded in the form of recording
marks having a length not shorter than the resolution limit of the
optical information storage medium reproduction apparatus 10, the
information may be read out first with low reproduction laser power
used for the normal double-layer optical information storage medium
100c or the like, followed by setting the reproduction laser power
Pr2 for the second information recording layer. Alternatively, the
reproduction laser power Pr2 for the second information recording
layer may be set by test reading with the use of a test read region
that is formed in advance in the double-layer super resolution
optical information storage medium 100d. That is, the reproduction
laser power may be caused to rise and fall so as to measure
reproduction laser power dependence of the reproduction signal
characteristic, and the reproduction laser power Pr2 for the second
information recording layer may be set, accordingly, so that its
value is selected from within a range of the reproduction laser
power.
[0164] Here, the reproduction laser power Pr1 for the first
information recording layer is not lower than the minimum
reproduction laser power Pr1 min for the first information
recording layer but lower than the reproduction laser power Pr2 for
the second information recording layer. A relationship among (a)
the reproduction laser power Pr1 for the first information
recording layer, (b) the reproduction laser power Pr2 for the
second information recording layer, and (c) the minimum
reproduction laser power Pr1min for the first information recording
layer satisfies the following expression (1):
Pr1min.ltoreq.Pr1<Pr2 (1)
[0165] One of the reasons why the reproduction laser power Pr1 for
the first information recording layer should be lower than the
reproduction laser power Pr2 for the second information recording
layer is as follows. As described above in "Reproduction Laser
Power in Conventional Optical Information Storage Medium
Reproduction Apparatus", in the conventional optical information
storage medium reproduction apparatus 10, the reproduction laser
power Pr1 for the first information recording layer and the
reproduction laser power Pr2 for the second information recording
layer are set to the same value. However, for the reading of the
first information recording layer 102d of the double-layer super
resolution optical information storage medium 100d, if the
reproduction laser power Pr1 for the first information recording
layer is equal to or higher than the reproduction laser power Pr2
for the second information recording layer, this may cause the
first information recording layer 102d to be unreadable. Further,
in a case where the reproduction laser power Pr1 for the first
information recording layer is lower than the minimum reproduction
laser power Pr1min for the first information recording layer, the
reproduction signal characteristic that the optical information
storage medium reproduction apparatus 10 requires cannot be
satisfied at the time of reading the first information recording
layer 102d. In this case, it is difficult to read the first
information recording layer 102d. For this reason, it is necessary
that the reproduction laser power Pr1 for the first information
recording layer should be not lower than the minimum reproduction
laser power Pr1min for the first information recording layer.
[0166] Further, a reproduction laser power range of the
reproduction laser power Pr1 for the first information recording
layer further preferably satisfies the following expression
(2):
1.05.times.Pr1min.ltoreq.Pr1.ltoreq.0.95.times.Pr2 (2)
[0167] One of the reasons is as follows. In general, there may
occur production variability between individual lasers and
assembling variability between individual optical systems in the
course of producing optical information storage medium reproduction
apparatuses, production variability between individual optical
information storage media, environmental differences at the time of
reproduction, and the like. In view of this, a reproduction laser
power margin, which is a reproduction laser power range for a
practical reproduction signal characteristic, is necessary for a
reproduction system. That is, the reproduction laser power margin
indicates an allowable range within which the reproduction laser
power may vary.
[0168] Generally, an amount of the reproduction laser power margin
becomes smaller, as accuracy of an optical pickup of the optical
system of the optical information storage medium reproduction
apparatus becomes higher, for example. However, since there is
variability between individual media, it is necessary that the
reproduction laser power margin have at least 5% latitude. In view
of this, the reproduction laser power Pr1 for the first information
recording layer is set such that each of an upper limit and a lower
limit of the reproduction laser power Pr1 has a 5% reproduction
laser power margin with respect to the range represented by the
expression (1) of the reproduction laser power Pr1 for the first
information recording layer. That is, the reproduction laser power
Pr1 for the first information recording layer is set so as to
satisfy the relationship represented by the expression (2). This
makes it possible to prevent that the reading of the first
information recording layer 102d of the double-layer super
resolution optical information storage medium 100d is affected by
various factors, such as production variability between individual
light sources for use in individual optical information storage
medium reproduction apparatuses 10, assembling variability between
individual optical systems for use in individual optical
information storage medium reproduction apparatuses 10, production
variability between individual double-layer super resolution
optical information storage media 100d, and environmental
differences at the time of reproduction.
[0169] As a result, it is possible that the reproduction signal
characteristic necessary for the optical information storage medium
reproduction apparatus 10 is satisfied. Besides, the changes in the
reflectance and the reproduction signal characteristic, which are
caused along with an increase in the number of reproduction times,
occur little as compared to the conventional optical information
storage medium reproduction apparatus. Consequently, the first
information recording layer 102d can be read stably.
[0170] How to determine the minimum reproduction laser power Pr1min
for the first information recording layer is not limited in any
particular manner, similarly to the reproduction laser power Pr2
for the second information recording layer. The minimum
reproduction laser power Pr1min for the first information recording
layer may be determined in the same manner as the reproduction
laser power Pr2 for the second information recording layer, as
described above. However, in a case where the minimum reproduction
laser power Pr1min for the first information recording layer is
determined according to the test reading, the minimum reproduction
laser power Pr1min for the first information recording layer is set
to a certain value by reflecting a result of the test reading,
differently from the reproduction laser power Pr2 for the second
information recording layer.
[0171] How to determine the reproduction laser power Pr1 for the
first information recording layer is also not limited in any
particular manner. However, it is necessary that the reproduction
laser power Pr1 be within the reproduction laser power range
represented by the expression (1), more preferably, the
reproduction laser power range represented by the expression (2),
each defined by the minimum reproduction laser power Pr1min for the
first information recording layer and the reproduction laser power
Pr2 for the second information recording layer.
[0172] (Movement Between Layers)
[0173] Next will be explained about the reproduction laser power
Pr1 for the first information recording layer and the reproduction
laser power Prn for the nth information recording layer at the time
when the optical information storage medium reproduction apparatus
moves focus (hereinafter also referred to as "focus movement
between layers") from the first information recording layer to the
nth information recording layer and vice versa during reproduction
of a multilayer super resolution optical information storage
medium. The following deals with a case, as an example, where the
double-layer super resolution optical information storage medium
100d is reproduced, i.e., a case where n=2.
[0174] At the time when the focus is moved (focus movement between
layers) from the first information recording layer 102d to the
second information recording layer 104d or from the second
information recording layer 104d to the first information recording
layer 102d, it is preferable that the reproduction laser power be
lower than the reproduction laser power Pr2 for the second
information recording layer.
[0175] In a case where the reproduction laser power is not lower
than the reproduction laser power Pr2 for the second information
recording layer at the time when the focus is moved from the first
information recording layer 102d to the second information
recording layer 104d or from the second information recording layer
104d to the first information recording layer 102d (that is, at the
time of focus movement between layers), the focus on the first
information recording layer 102d with such high reproduction laser
power may cause the first information recording layer 102d to be
unreadable irreversibly due to the high reproduction laser power.
In contrast, in a case where the reproduction laser power is lower
than the reproduction laser power Pr2 for the second information
recording layer, it is possible to prevent the above problem in
which the first information recording layer 102d is rendered
unreadable irreversibly.
[0176] Further, it is more preferable that the reproduction laser
power used at the time when the focus is moved from the first
information recording layer 102d to the second information
recording layer 104d or from the second information recording layer
104d to the first information recording layer 102d (i.e., at the
time of focus movement between layers) be the reproduction laser
power Pr1 for the first information recording layer. One of the
reasons is as follows.
[0177] Assume that Prx is reproduction laser power which is lower
than the reproduction laser power Pr2 for the second information
recording layer but which is not the reproduction laser power Pr1
for the first information recording layer. Prx is taken as
reproduction laser power at the time when the focus is moved from
the first information recording layer 102d to the second
information recording layer 104d or from the second information
recording layer 104d to the first information recording layer 102d
(at the time of focus movement between layers).
[0178] In this case, the reproduction laser power Prx is different
from the reproduction laser power Pr1 for the first information
recording layer and the reproduction laser power Pr2 for the second
information recording layer. Therefore, it is necessary that the
reproduction laser power be once set to Prx before it is changed
from the reproduction laser power Pr1 for the first information
recording layer to the reproduction laser power Pr2 for the second
information recording layer and vice versa. This causes time loss
because one focus movement between layers requires two changes in
laser power. Further, if Prx is largely different from the
reproduction laser power Pr1 for the first information recording
layer and the reproduction laser power Pr2 for the second
information recording layer, this may causes such a problem that
the focus on each of the information recording layers may become
poor.
[0179] In view of this, if the reproduction laser power is set to
the reproduction laser power Pr1 for the first information
recording layer at the time when the focus is moved from the first
information recording layer 102d to the second information
recording layer 104d or from the second information recording layer
104d to the first information recording layer 102d (at the time of
focus movement between layers), it is possible to prevent time loss
and poor focus.
[0180] The above description deals with the optical information
storage medium reproduction apparatus 10 that is capable of
reproducing the double-layer super resolution optical information
storage medium 100d as one of examples of the super resolution
optical information storage medium. However, the double-layer super
resolution optical information storage medium may be an n-layer
optical information storage medium (n.gtoreq.2), the second
information recording layer 104d may be an nth information
recording layer, and the reproduction laser power Pr2 for the
second information recording layer may be reproduction laser power
Prn for the nth information recording layer. That is, the optical
information storage medium reproduction apparatus may be an optical
information storage medium reproduction apparatus that is capable
of reproducing a multilayer super resolution optical information
storage medium having n (n is an integer not less than 2) pieces of
information recording layers.
[0181] One of the reasons is that a relationship between the first
information recording layer and the nth information recording layer
in reproduction laser power and endurance does not change
regardless of whether n is 2 or not less than 2.
[0182] This is apparent from the following fact, for example. That
is, the nth information recording layer is read definitely with
reproduction light that has passed through the first information
recording layer. Therefore, in order to obtain a temperature and
light amount necessary for the super resolution reproduction,
reproduction laser power higher than power necessary for the first
information recording layer is required.
[0183] Further, another reason is as follows. That is, since the
first information recording layer needs to pass light therethrough
to some extent so as to enable the reading of the nth information
recording layer, it is necessary that a reflection film, a
light-absorbing layer, and a functional layer should be formed
thin. This causes unstable states of materials and the like,
thereby resulting in that the change in reflectance or the like in
the first information recording layer becomes large along with an
increase in the number of reproduction times.
[0184] (Advantageous Effects of the Present Invention)
[0185] In addition to the above description, the present invention
can be described as follows. That is, the present invention relates
to an optical information storage medium reproduction apparatus for
reproducing an optical information storage medium in which
information is stored with high density.
[0186] The present invention relates to an optical information
storage medium reproduction apparatus for recording and reproducing
information with the use of light such as a laser beam or the like,
or for reading a read-only optical information storage medium. More
specifically, the present invention relates to an optical
information storage medium reproduction apparatus for reproducing
an optical information storage medium, a method for reproducing an
optical information storage medium and an optical information
storage medium, each of which employs a super resolution optical
information storage medium technique for reading a recording mark
that is not longer than an optical resolution limit defined by a
light spot diameter at diffraction limit.
[0187] An optical information storage medium reproduction apparatus
of the present invention is an optical information storage medium
reproduction apparatus that is capable of reproducing a multilayer
optical information storage medium having n (n is an integer not
less than 2) pieces of information recording layers including a
reproduction film that allows reading of a recording mark shorter
than a resolution limit of the optical information storage medium
reproduction apparatus. The optical information storage medium
reproduction apparatus satisfies Pr1min.ltoreq.Pr1<Prn, where
Pr1 is reproduction laser power for reading a first information
recording layer, which is closest to a reproduction-light-incident
surface of the optical information storage medium, Prn is
reproduction laser power for reading an nth information recording
layer, which is farthest from the reproduction-light-incident
surface, and Pr1min is minimum reproduction laser power that
satisfies a reproduction signal characteristic necessary for the
optical information storage medium reproduction apparatus at the
time of reading the first information recording layer.
[0188] With the arrangement, at the time of reading the first
information recording layer, which is closest to the
reproduction-light-incident surface of the multilayer super
resolution optical information storage medium, the reproduction
signal characteristic necessary for the optical information storage
medium reproduction apparatus is satisfied, thereby preventing a
decrease in reflectance and a deterioration in reproduction signal
characteristic along with an increase in the number of reproduction
times, as compared with a conventional optical information storage
medium reproduction apparatus. As a result, it is possible to
stably read the first information recording layer.
[0189] An optical information storage medium reproduction apparatus
of the present invention is an optical information storage medium
reproduction apparatus (i) which is capable of reproducing a
multilayer optical information storage medium having n (n is an
integer not less than 2) pieces of information recording layers
each having a recording mark shorter than 120 nm and (ii) which
includes an optical system including a laser that irradiates light
having a wavelength of about 405 nm and an objective lens having a
numerical aperture of substantially 0.85. The optical information
storage medium reproduction apparatus satisfies
Pr1min.ltoreq.Pr1<Prn, where Pr1 is reproduction laser power for
reading a first information recording layer, which is closest to a
reproduction-light-incident surface of the optical information
storage medium, Prn is reproduction laser power for reading an nth
information recording layer, which is farthest from the
reproduction-light-incident surface, and Pr1min is minimum
reproduction laser power that satisfies a reproduction signal
characteristic necessary for the optical information storage medium
reproduction apparatus at the time of reading the first information
recording layer.
[0190] In this arrangement, the optical information storage medium
reproduction apparatus of the present invention includes an optical
system including a laser that irradiates light having a blue laser
wavelength like a Blu-ray Disc (registered trademark) reproduction
apparatus and an objective lens having a numerical aperture of
substantially 0.85. Further, in the arrangement, the optical
information storage medium reproduction apparatus satisfies its
necessary reproduction signal characteristic at the time of reading
a first information recording layer, which is closest to a
reproduction-light-incident surface of a read-only type multilayer
super resolution optical information storage medium. Consequently,
with the arrangement, it is possible to prevent a decrease in
reflectance and a deterioration in reproduction signal
characteristic along with an increase in the number of reproduction
times, as compared to a conventional optical information storage
medium reproduction apparatus, thereby allowing stable reading of
the first information recording layer.
[0191] An optical information storage medium reproduction apparatus
of the present invention is an optical information storage medium
reproduction apparatus (i) which includes an optical system
including a laser that irradiates light having a wavelength of
substantially 405 nm and an objective lens having a numerical
aperture of substantially 0.85 and (ii) which is capable of
reproducing a multilayer optical information storage medium having
n (n is an integer not less than 2) pieces of information recording
layers in which information is stored in the form of a plurality of
recording marks including a recording mark shorter than 120 nm. The
optical information storage medium reproduction apparatus satisfies
Pr1min.ltoreq.Pr1<Prn, where Pr1 is reproduction laser power for
reading a first information recording layer, which is closest to a
reproduction-light-incident surface of the optical information
storage medium, Prn is reproduction laser power for reading an nth
information recording layer, which is farthest from the
reproduction-light-incident surface, and Pr1min is minimum
reproduction laser power that satisfies a reproduction signal
characteristic necessary for the optical information storage medium
reproduction apparatus at the time of reading the first information
recording layer.
[0192] In this arrangement, the optical information storage medium
reproduction apparatus of the present invention includes an optical
system including a laser that irradiates light having a blue laser
wavelength like a Blu-ray Disc (registered trademark) reproduction
apparatus and an objective lens having a numerical aperture of
substantially 0.85. Further, the optical information storage medium
reproduction apparatus satisfies its necessary reproduction signal
characteristic at the time of reading a first information recording
layer, which is closest to a reproduction-light-incident surface of
a writable type multilayer super resolution optical information
storage medium. Consequently, with the arrangement, it is possible
to prevent a decrease in reflectance and a deterioration in
reproduction signal characteristic along with an increase in the
number of reproduction times, as compared to a conventional optical
information storage medium reproduction apparatus, thereby allowing
stable reading of the first information recording layer.
[0193] The optical information storage medium reproduction
apparatus of the present invention satisfies
1.05.times.Pr1min.ltoreq.Pr1.ltoreq.0.95.times.Prn.
[0194] Here, the optical information storage medium reproduction
apparatus requires a margin for reproduction power for its
reproduction system so as to cope with environmental differences at
the time of reproduction. The environmental differences at the time
of reproduction may encompass production variability between
individual lasers for use in individual optical information storage
medium reproduction apparatuses, assembling variability between
individual optical systems for use in individual optical
information storage medium reproduction apparatuses, production
variability between individual optical information storage media,
and the like.
[0195] Further, as the optical information storage medium
reproduction apparatus is more accurate, a necessary amount of the
margin becomes smaller. However, a general optical information
storage medium reproduction apparatus requires a margin ratio of at
least 5%. On this account, in the present invention, Pr1 is set
such that each of an upper limit and a lower limit of Pr1 has a 5%
reproduction power margin. That is, the optical information storage
medium reproduction apparatus of the present invention satisfies
1.05.times.Pr1min.ltoreq.Pr1.ltoreq.0.95.times.Prn.
[0196] With the arrangement, the optical information storage medium
reproduction apparatus of the present invention satisfies its
necessary reproduction signal characteristic at the time of reading
a first information recording layer, which is closest to a
reproduction-light-incident surface of a multilayer super
resolution optical information storage medium, without being
affected by production variability between individual lasers for
use in individual optical information storage medium reproduction
apparatuses, assembling variability between individual optical
systems for use in individual optical information storage medium
reproduction apparatuses, production variability between individual
optical information storage media, and environmental differences at
the time of reproduction. As a result, it is possible to restrain a
decrease in reflectance and a deterioration in reproduction signal
characteristic along with an increase in the number of reproduction
times, as compared to a conventional optical information storage
medium reproduction apparatus, thereby making it possible to more
stably read the first information recording layer.
[0197] The optical information storage medium reproduction
apparatus of the present invention is arranged such that
reproduction laser power is set lower than Prn at the time of
moving its focus (hereinafter just referred to as "movement between
layers) from a first information recording layer onto an nth
information recording layer or from the nth information recording
layer onto the first information recording layer.
[0198] In a case where the reproduction laser power is set not
lower than Prn at the time of moving the focus from the nth
information recording layer onto the first information recording
layer, there may occur such a problem that the first information
recording layer may be rendered unreadable irreversibly. In
contrast, if the reproduction laser power is set lower than Prn at
this time, it is possible to prevent the problem that the first
information recording layer is rendered unreadable irreversibly.
The reproduction laser power is preferably set to Pr1.
[0199] Assume Prx is reproduction laser power which is lower than
Prn but which is not Pr1 and the reproduction laser power is set to
Prx at the time of moving the focus from the first information
recording layer to the nth information recording layer or from the
nth information recording layer to the first information recording
layer. At this time, the reproduction laser power is set to a value
that is different from both reproduction laser power Pr1 for the
first information recording layer and reproduction laser power Prn
for the nth information recording layer. Therefore, the
reproduction laser power should be once set to Prx before the
reproduction laser power is changed from Pr1 to Prn and vice versa.
That is, the laser power should be changed in two stages for one
focus movement between layers, thereby causing the focus movement
between layers to take time. Further, if Prx is set to a value
largely different from Pr1 or Prn, there may occur such a problem
that the focus on each of the information recording layers may
become poor.
[0200] For these reasons, when the reproduction laser power is set
to Pr1 at the time of the focus movement between layers, it is
possible to focus an intended information recording layer in a time
efficient manner.
[0201] The optical information storage medium reproduction
apparatus of the present invention performs reproduction in the
order from a first information recording layer in a case of an
optical information storage medium where n=2. In a case of an
optical information storage medium reproduction apparatus that
reads a second information recording layer first, there may occur
such a problem that the first information recording layer is
focused accidentally so that the first information recording layer
is read with Pr2, which is high reproduction laser power, thereby
causing the first information recording layer to be unreadable
irresistibly. In contrast, with the above arrangement, since the
optical information storage medium reproduction apparatus of the
present invention reads the first information recording layer
first, it is possible to prevent such a problem. Further, in a case
where a double-layer super resolution optical information storage
medium, where n=2, is a medium from which the optical information
storage medium reproduction apparatus can identify values of Pr1
and Pr2 before it starts to reproduce the medium, the optical
information storage medium reproduction apparatus starts to read
the first information recording layer with Pr1 and the second
information recording layer with Pr2. This yields an effect that
the reproduction can be performed in a time efficient manner.
[0202] The present embodiment discloses an optical information
storage medium reproduction apparatus for reproducing an optical
information storage medium. However, the present invention is not
limited to this, and may include a read-only or write-only
apparatus and a read/write apparatus. Further, the usage of such an
apparatus is not limited in any particular manner, and the
apparatus may be stationary, portable, or the like.
[0203] As described above, an optical information storage medium
reproduction apparatus, according to the present invention, for
reproducing an optical information storage medium in which a
plurality of information recording layers are laminated, each of
the plurality of information recording layers including a recording
mark having a length shorter than an optical system resolution
limit. The optical information storage medium reproduction
apparatus of the present invention reads an information recording
layer closest to a reproduction-laser-incident surface of the
optical information storage medium, with reproduction laser power
that is set to be lower than reproduction laser power for reading
an information recording layer farthest from the
reproduction-laser-incident surface but not lower than minimum
reproduction laser power that satisfies a reproduction signal
characteristic necessary for the optical information storage medium
reproduction apparatus.
[0204] Further, an optical information storage medium reproduction
apparatus according to the present invention, is an optical
information storage medium for reproducing an optical information
storage medium in which a plurality of information recording layers
are laminated, each of the plurality of information recording
layers including a recording mark having a length not longer than
120 nm, the optical information storage medium reproduction
apparatus includes an optical system including a laser light source
capable of irradiating laser light having a wavelength of not less
than 400 nm but not more than 410 nm and an objective lens having a
numerical aperture of not less than 0.83 but not more than 0.87.
The optical information storage medium reproduction apparatus of
the present invention reads an information recording layer closest
to a reproduction-laser-incident surface of the optical information
storage medium, with reproduction laser power that is set to be
lower than reproduction laser power for reading an information
recording layer farthest from the reproduction-laser-incident
surface but not lower than minimum reproduction laser power that
satisfies a reproduction signal characteristic that the optical
information storage medium reproduction apparatus requires.
[0205] Furthermore, an optical information storage medium
reproduction apparatus according to the present invention is an
optical information storage medium reproduction apparatus for
reproducing an optical information storage medium in which a
plurality of information recording layers are laminated, each of
the plurality of information recording layers including a recording
mark having a length not longer than 120 nm, the optical
information storage medium reproduction apparatus includes an
optical system including a laser light source capable of
irradiating laser light having a wavelength of not less than 400 nm
but not more than 410 nm and an objective lens having a numerical
aperture of 0.85. The optical information storage medium
reproduction apparatus of the present invention reads an
information recording layer closest to a
reproduction-laser-incident surface of the optical information
storage medium, with reproduction laser power that is set to be
lower than reproduction laser power for reading an information
recording layer farthest from the reproduction-laser-incident
surface but not lower than minimum reproduction laser power that
satisfies a reproduction signal characteristic that the optical
information storage medium reproduction apparatus requires.
[0206] A control method, according to the present invention is a
method for controlling an information storage medium reproduction
apparatus for reading an optical information storage medium in
which a plurality of information recording layers are laminated,
each of the plurality of information recording layers including a
recording mark having a length shorter than an optical system
resolution limit. The control method of the present invention
includes setting, at the time of reading an information recording
layer closest to a reproduction-laser-incident surface of the
optical information storage medium, reproduction laser power to be
lower than reproduction laser power for reading an information
recording layer farthest from the reproduction-laser-incident
surface but not lower than minimum reproduction laser power that
satisfies a reproduction signal characteristic that the optical
information storage medium reproduction apparatus requires.
[0207] In the above arrangement, at the time of reading the
information recording layer closest to the
reproduction-laser-incident surface of the optical information
storage medium, the optical information storage medium reproduction
apparatus sets reproduction laser power to be lower than
reproduction laser power for reading the information recording
layer farthest from the reproduction-laser-incident surface but not
lower than minimum reproduction laser power that satisfies a
reproduction signal characteristic that the optical information
storage medium reproduction apparatus requires. Accordingly, the
optical information storage medium reproduction apparatus reads the
information recording layer closest to the
reproduction-laser-incident surface by irradiating the information
recoding layer with laser light having the reproduction laser power
thus set. As a result, with the above arrangement, it is possible
to prevent that the information recording layer closest to the
reproduction-laser-incident surface is read with inappropriately
high reproduction laser power, thereby making it possible to
prevent a decrease in reflectance and a deterioration in
reproduction signal characteristic along with repeat reproduction.
Consequently, it is possible to stably reproduce a multilayer super
resolution optical information storage medium like the above
optical information storage medium.
[0208] In a case where a conventional optical information storage
medium reproduction apparatus reproduces a multilayer information
storage medium including n (n is an integer not less than 2)
information recording layers, the same reproduction laser power is
employed to read a first information recording layer, which is
first from the reproduction-laser-incident surface, and an nth
information recording layer, which is nth from the
reproduction-laser-incident surface. For example, in a case where a
conventional double-layer optical information storage medium is
reproduced, the first information recording layer and the second
information recording layer are read with the same reproduction
laser power.
[0209] In view of this, the inventor(s) of the present invention
found the following fact. That is, in the case where the first
information recording layer and the second information recording
layer of the double-layer super resolution optical information
storage medium are read with the same reproduction laser power as
such, recording marks of the first information recording layer are
damaged, thereby resulting in that information stored in the first
information recording layer is rendered unreadable.
[0210] The above arrangement of the present invention is applicable
to an optical information storage medium reproduction apparatus
including an optical system constituted by (i) a laser light source
capable of irradiating laser light which is like a blue laser
employed by a Blu-ray Disc (registered trademark) reproduction
apparatus and which has a wavelength of not less than 400 nm but
not more than 410 nm, and (ii) an objective lens having a numerical
aperture of 0.85. It should be noted that even if the numerical
aperture has an error of around .+-.0.02, it hardly affects the
advantageous effects of the present invention. On this account, the
numerical aperture may be not less than 0.83 but not more than
0.87.
[0211] Furthermore, the above arrangement of the present invention
is also applicable to reading of information recording layers, such
as an information recording layer on which a plurality of recording
marks including a recording mark shorter than 120 nm have been
formed, and an information recording layer in which information is
to be recorded in the form of a plurality of recording marks
including a recording mark shorter than 120 nm.
[0212] The above optical information storage medium may be a
read-only optical information storage medium (read-only type) in
which information has been already recorded, or an optical
information storage medium (writable/readable type) in which a
piece of information has been partially recorded and another piece
of the information may be additionally recorded and in which the
piece of information has been recorded in at least one of a
plurality of information recording layers.
[0213] In addition, the optical information recording medium
reproduction apparatus according to the present invention is
arranged such that the reproduction laser power with which the
optical information recording medium reproduction apparatus reads
the information recording layer closest to the
reproduction-laser-incident surface is set to be not higher than
0.95 times the reproduction laser power for reading the information
recording layer farthest from the reproduction-laser incident
surface, but not lower than 1.05 times the minimum reproduction
laser power that satisfies the reproduction signal characteristic
that the optical information recording layer requires at the time
of reading the information recording layer closest to the
reproduction-laser-incident surface.
[0214] Generally, there are various factors that affect quality in
reproduction at the time of reproduction. Examples of such factors
are production variability between individual lasers for use in
individual optical information storage medium reproduction
apparatuses, assembling variability between individual optical
systems for use in individual optical information storage medium
reproduction apparatuses, production variability between individual
optical information storage media, and environmental differences at
the time of reproduction.
[0215] In order to cope with such factors, a reproduction laser
power margin, which is a reproduction laser power range for a
practical reproduction signal characteristic, is required. More
specifically, the reproduction laser power margin indicates an
allowable range within which the reproduction laser power may vary.
Generally, as accuracy of, for example, an optical pickup of the
optical system of the optical information storage medium
reproduction apparatus becomes higher, an amount of the
reproduction laser power margin becomes smaller. However, since
there is variability between individual media and the like, it is
necessary that the reproduction laser power have at least 5%
latitude with respect to each of theoretical upper limit and lower
limit.
[0216] As such, in the above arrangement, the reproduction laser
power margin has at least 5% latitude with respect to each of the
theoretical upper limit and lower limit. As a result, the
arrangement further makes it possible that the reproduction can be
performed without being affected by production variability between
individual laser light sources for use in individual optical
information storage medium reproduction apparatuses, assembling
variability between individual optical systems for use in
individual optical information storage medium reproduction
apparatuses, production variability between individual optical
information storage media, environmental differences at the time of
reproduction, and the like.
[0217] Further, the optical information storage medium reproduction
apparatus of the present invention is arranged such that at the
time of focus movement from an information recording layer onto
another information recording layer, the optical information
storage medium reproduction apparatus moves the focus from the
information recording layer to the another information recording
layer with reproduction laser power being maintained to be lower
than the reproduction laser power for reading the information
recording layer farthest from the reproduction-laser-incident
surface.
[0218] With the arrangement, even when the focus is moved from the
information recording layer farthest from the
reproduction-laser-incident surface onto the information recording
layer closest to the reproduction-laser-incident surface and vice
versa, it is possible to restrain that the information recording
layer closest to the reproduction-laser-incident surface is read
with inappropriately high reproduction laser power. This results in
that it is possible to prevent a decrease in reflectance and a
deterioration in reproduction signal characteristic along with
repeat reproduction.
[0219] In the above arrangement, it is preferable that the optical
information storage medium reproduction apparatus move the focus
from the information recording layer to the another information
recording layer with reproduction laser power for reading one of
the information recording layers that is closer to the
reproduction-laser-incident surface.
[0220] In the arrangement, when the focus is moved between layers,
the reproduction laser power is changed only once. This can improve
efficiency and further prevent poor focus.
[0221] Further, the optical information storage medium reproduction
apparatus according to the present invention is arranged such that
in a case where the optical information storage medium includes 2
information recording layers, the optical information storage
medium reproduction apparatus reproduces the optical information
storage medium in the order from one of the 2 information recording
layers that is closer to the reproduction-laser-incident surface
than the other one of the 2 information recording layers.
[0222] Assume that an optical information storage medium
reproduction apparatus reproduces a double-layer optical
information storage medium, which includes 2 information recording
layers, and the optical information storage medium reproduction
apparatus performs reproduction in the order from one of the
information recording layers that is farther from a
reproduction-laser-incident surface of the medium than the other
one. In this case, if the other one of the information recording
layers that is closer to the reproduction-laser-incident surface is
read wrongly with reproduction laser power for the information
recording layer farther from the reproduction-laser-incident
surface, there may occur such a problem that the information
recording layer closer to the reproduction-laser-incident surface
is rendered unreadable irreversibly.
[0223] However, with the above arrangement of the present
invention, it is possible to prevent that the information recording
layer closer to the reproduction-laser-incident surface is
irradiated with light having such inappropriately high reproduction
laser power, thereby preventing a deterioration in reproduction
characteristic of the information recording layer closer to the
reproduction-laser-incident surface.
[0224] The present invention is not limited to the description of
the embodiments above, but may be altered by a skilled person
within the scope of the claims. An embodiment based on a proper
combination of technical means disclosed in different embodiments
is encompassed in the technical scope of the present invention.
INDUSTRIAL APPLICABILITY
[0225] The present invention can be widely and preferably applied
to an optical information storage medium reproduction apparatus and
the like which performs super resolution reproduction of a
multilayer optical information storage medium.
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