U.S. patent application number 10/105537 was filed with the patent office on 2002-10-03 for high density optical disk and a method of high density recording.
Invention is credited to Hayashi, Masatoshi, Matsumoto, Hiroyuki, Morita, Seiji, Yoshibe, Satomi.
Application Number | 20020141328 10/105537 |
Document ID | / |
Family ID | 27547552 |
Filed Date | 2002-10-03 |
United States Patent
Application |
20020141328 |
Kind Code |
A1 |
Matsumoto, Hiroyuki ; et
al. |
October 3, 2002 |
High density optical disk and a method of high density
recording
Abstract
The current invention is directed to a high density disk and a
method of manufacturing the high density disk. The high density is
accomplished by narrowing the pitch and increasing the groove depth
so as not to sacrifice any desirable features of the high density
optical disk medium.
Inventors: |
Matsumoto, Hiroyuki; (Tokyo,
JP) ; Morita, Seiji; (Yokohama-shi, JP) ;
Hayashi, Masatoshi; (Kawasaki-Shi, JP) ; Yoshibe,
Satomi; (Kawasaki-shi, JP) |
Correspondence
Address: |
WOODCOCK WASHBURN LLP
ONE LIBERTY PLACE, 46TH FLOOR
1650 MARKET STREET
PHILADELPHIA
PA
19103
US
|
Family ID: |
27547552 |
Appl. No.: |
10/105537 |
Filed: |
March 25, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10105537 |
Mar 25, 2002 |
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09264735 |
Mar 9, 1999 |
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09264735 |
Mar 9, 1999 |
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08760636 |
Dec 4, 1996 |
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Current U.S.
Class: |
369/275.4 ;
G9B/7.029; G9B/7.031; G9B/7.194 |
Current CPC
Class: |
G11B 7/007 20130101;
G11B 7/00718 20130101; G11B 11/10584 20130101; G11B 7/24079
20130101; G11B 7/26 20130101 |
Class at
Publication: |
369/275.4 |
International
Class: |
G11B 007/24 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 5, 1995 |
JP |
7-316595 |
Jan 8, 1996 |
JP |
8-000810 |
Mar 12, 1996 |
JP |
8-054488 |
Feb 19, 1996 |
JP |
8-042995 |
Apr 16, 1996 |
JP |
8-094539 |
Claims
What is claimed is:
1. A method of manufacturing optical disks for substantially
reducing cross-talk during input and output operations to and from
the optical disks each having grooves and lands, data being stored
on both the grooves and lands, comprising the steps of: a)
specifying a track pitch between the grooves and the lands; b)
selecting a depth of the grooves d in relation to the lands to
satisfy a first relation, d=.lambda./(an) where a is a parameter
variable, .lambda. is a laser wavelength used during the operations
and n is a refraction index of an optical disk substrate; and c)
further selecting said depth d so as to make the cross-talk equal
to or less than -25 dB while said first relation in said step b) is
maintained.
2. The method of substantially reducing cross-talk according to
claim 1 wherein said parameter a is equal to or less than 4.
3. The method of substantially reducing cross-talk according to
claim 1 wherein said track pitch is equal to or less than 1.1
.lambda..
4. The method of substantially reducing cross-talk according to
claim 1 wherein said track pitch is equal to or less than 0.96
.lambda..
5. The method of substantially reducing cross-talk according to
claim 1 wherein said track pitch is equal to or less than 0.81
.lambda..
6. The method of substantially reducing cross-talk according to any
one of claims 3, 4, and 5 wherein said wavelength is equal to or
less than 690 nm.
7. A method of manufacturing optical disks for substantially
reducing cross-talk during input and output operations to and from
the optical disks each having grooves and lands, data being stored
on both the grooves and lands, comprising the steps of: a)
specifying a track pitch between the grooves and the lands; and b)
selecting a depth of the grooves d in relation to the lands to
satisfy a first relation, d=.lambda./(an) where a is a parameter
variable, .lambda. is a laser wavelength used during the operations
and n is a refraction index of an optical disk substrate, said
parameter ranges from 2.8 to 3.4.
8. The method of substantially reducing cross-talk according to
claim 7 wherein said track pitch is equal to or less than 1.1
.lambda..
9. The method of substantially reducing cross-talk according to
claim 7 wherein said track pitch is equal to or less than 0.96
.lambda..
10. The method of substantially reducing cross-talk according to
claim 7 wherein said track pitch is equal to or less than 0.81
.lambda..
11. The method of substantially reducing cross-talk according to
any one of claims 8, 9, and 10 wherein said wavelength is equal to
or less than 690 nm.
12. A method of manufacturing optical disks for substantially
reducing cross-talk during input and output operations to and from
the optical disks each having grooves and lands, data being stored
on both the grooves and lands, comprising the steps of: a)
specifying a track pitch between the grooves and the lands; b)
selecting a depth of the grooves d in relation to the lands to
satisfy a first relation, d=.lambda./(an)+m.lambda./(bn) where a
and b are parameter variables, .lambda. is a laser wavelength used
during the operations, m is an integer and n is a refraction index
of an optical disk substrate, wherein said parameter a satisfies
5.2.ltoreq.a.ltoreq.6.8 while said parameter b satisfies
1.8.ltoreq.b.ltoreq.2.1, m being a natural number.
13. The method of substantially reducing cross-talk according to
claim 12 wherein said parameter a satisfies 2.8 s a s 3.4 while
said parameter b satisfies 1.8.ltoreq.b.ltoreq.2.1, m being a
positive integer including 0.
14. The method of substantially reducing cross-talk according to
claim 12 wherein said track pitch is equal to or less than 1.1
.lambda..
15. The method of substantially reducing cross-talk according to
claim 12 wherein said track pitch is equal to or less than 0.96
.lambda..
16. The method of substantially reducing cross-talk according to
claim 12 wherein said track pitch is equal to or less than 0.81
.lambda..
17. The method of substantially reducing cross-talk according to
any one of claims 14, 15 and 16 wherein said wavelength is equal to
or less than 690 nm.
18. A method of manufacturing optical disks for substantially
reducing thermal cross-talk during input and output operations to
and from the optical disks each having grooves and lands comprising
the steps of: a) specifying a track pitch between the grooves and
the lands to be equal or less than 1.1 .lambda. where .lambda. is a
laser wavelength used during the operations; and b) selecting a
depth of the grooves d in relation to the lands to satisfy a first
relation, d=.lambda./(an) where a is a parameter variable and n is
a refraction index of an optical disk substrate.
19. The method of manufacturing optical disks according to claim 18
wherein said parameter a ranges from 2.159 to 3.778.
20. The method of manufacturing optical disks according to claim 18
wherein said parameter a ranges from 2.061 to 3.487.
21. The method of manufacturing optical disks according to claim 18
wherein said parameter a ranges from 2.061 to 3.022.
22. The method of manufacturing optical disks according to claim 18
wherein said parameter a ranges from 1.365 to 1.959.
23. The method of manufacturing optical disks according to claim 18
wherein said parameter a ranges from 0.776 to 1.288.
24. The method of manufacturing optical disks according to claim 18
wherein said wavelength .lambda. is equal to or less than 690
nm.
25. A method of manufacturing optical disks for substantially
reducing thermal cross-talk during input and output operations to
and from the optical disks each having grooves and lands comprising
the steps of: a) specifying a track pitch between the grooves and
the lands to be equal or less than 0.96 .lambda. where .lambda. is
a laser wavelength used during the operations; and b) selecting a
depth of the grooves d in relation to the lands to satisfy a first
relation, d=.lambda./(an) where a is a parameter variable and n is
a refraction index of an optical disk substrate.
26. The method of manufacturing optical disks according to claim 25
wherein said parameter a ranges from 2.159 to 3.778.
27. The method of manufacturing optical disks according to claim 25
wherein said parameter a ranges from 2.159 to 3.238.
28. The method of manufacturing optical disks according to claim 25
wherein said parameter a ranges from 2.061 to 3.487.
29. The method of manufacturing optical disks according to claim 25
wherein said parameter a ranges from 2.061 to 2.667.
30. The method of manufacturing optical disks according to claim 25
wherein said parameter a ranges from 1.365 to 1.959.
31. The method of manufacturing optical disks according to claim 25
wherein said parameter a ranges from 0.776 to 1.288.
32. The method of manufacturing optical disks according to claim 25
wherein said wavelength .lambda. is equal to or less than 690
nm.
33. A method of manufacturing optical disks for substantially
reducing thermal cross-talk during input and output operations to
and from the optical disks each having grooves and lands comprising
the steps of: a) specifying a track pitch between the grooves and
the lands to be equal or less than 0.81 .lambda. where .lambda. is
a laser wavelength used during the operations; and b) selecting a
depth of the grooves d in relation to the lands to satisfy a first
relation, d=.lambda./(an) where a is a parameter variable and n is
a refraction index of an optical disk substrate.
34. The method of manufacturing optical disks according to claim 33
wherein said parameter a ranges from 2.267 to 3.778.
35. The method of manufacturing optical disks according to claim 33
wherein said parameter a ranges from 2.159 to 3.022.
36. The method of manufacturing optical disks according to claim 33
wherein said parameter a ranges from 2.159 to 3.238.
37. The method of manufacturing optical disks according to claim 33
wherein said parameter a ranges from 2.159 to 2.386.
38. The method of manufacturing optical disks according to claim 33
wherein said parameter a ranges from 1.365 to 1.959.
39. The method of manufacturing optical disks according to claim 33
wherein said parameter a ranges from 0.776 to 1.288.
40. The method of manufacturing optical disks according to claim 33
wherein said wavelength .lambda. is equal to less than 690 nm.
41. A method of manufacturing optical disks for substantially
reducing thermal cross-talk during input and output operations to
and from the optical disks each having grooves and lands comprising
the steps of: a) specifying a track pitch between the grooves and
the lands to be equal or less than 1.1 .lambda. where .lambda. is a
laser wavelength used during the operations; and b) selecting a
depth of the grooves d in relation to the lands to satisfy a first
relation, d>.lambda./(4n) where n is a refraction index of an
optical disk substrate.
42. The method of manufacturing optical disks according to claim 41
wherein said wavelength .lambda. is equal to or less than 690
nm.
43. The method of manufacturing optical disks according to claim 41
further comprising a step c) of further selecting said depth d so
as to make I.sub.PP/I.sub.O.gtoreq.0.2.
44. The method of manufacturing optical disks according to claim 41
further comprising a step c) of further selecting said depth d so
as to make I.sub.G/I.sub.O.gtoreq.0.5.
45. The method of manufacturing optical disks according to claim 41
further comprising a step c) of further selecting said depth d so
as to make Pe/Pp.gtoreq.1.2.
46. The method of manufacturing optical disks according to claim 41
further comprising a step c) of further selecting said depth d so
as to make Pe/Pp.gtoreq.1.3.
47. A method of manufacturing optical disks for substantially
reducing thermal cross-talk during input and output operations to
and from the optical disks each having grooves and lands, data
being stored on both the grooves and lands, comprising the steps
of: a) specifying a track pitch between the grooves and the lands
at a predetermined width ratio of the grooves and the lands; and b)
selecting a depth of the grooves d in relation to the lands to
satisfy a first relation, d>.lambda./(4n) where .lambda. is a
laser wavelength used during the operations and n is a refraction
index of an optical disk substrate.
48. The method of manufacturing optical disks according to claim 47
wherein said wavelength .lambda. is equal to or less than 690
nm.
49. The method of manufacturing optical disks according to claim 47
wherein said predetermined width ratio is larger than 1.
50. The method of manufacturing optical disks according to claim 47
wherein said predetermined width ratio is equal to or larger than
1.05.
51. The method of manufacturing optical disks according to claim 47
wherein said predetermined width ratio is equal to or larger than
1.08.
52. The method of manufacturing optical disks according to claim 47
wherein said predetermined width ratio is equal to or larger than
1.1.
53. The method of manufacturing optical disks according to claim 47
wherein said track pitch is equal to or less than 1.1 .lambda..
54. The method of manufacturing optical disks according to claim 47
wherein said track pitch is equal to or less than 0.96
.lambda..
55. The method of manufacturing optical disks according to claim 47
wherein said track pitch is equal to or less than 0.81
.lambda..
56. The method of manufacturing optical disks according to claim 47
further comprising a step b) of further selecting said depth d so
as to make Pp(groove)/Pp(land).gtoreq.80.
57. The method of manufacturing optical disks according to claim 38
further comprising a step b) of further selecting said depth d so
as to make Pp(groove)/Pp(land).gtoreq.85.
58. An optical disk for substantially reducing cross-talk during
its input and output operations to and from the optical disks,
comprising: grooves and lands located on the disk for storing data
on both said grooves and said lands, a predetermined distance
between said grooves and said lands being defined as a
predetermined track pitch, wherein said grooves having a depth d in
relation to said lands, wherein said depth is related to a
parameter variable a, a laser wavelength .lambda. which is used
during the operations and a refraction index n of an optical disk
substrate in a relation as (d)>.lambda./(an), said depth d is
further determined so that cross-talk is equal to or less than -25
dB while said relation is maintained.
59. The optical disk for substantially reducing cross-talk
according to claim 58 wherein said parameter a is equal to or less
than 4.
60. The optical disk for substantially reducing cross-talk
according to claim 58 wherein said predetermined track pitch is
equal to or less than 1.1 .lambda..
61. The optical disk for substantially reducing cross-talk
according to claim 58 wherein said track pitch is equal to or less
than 0.96 .lambda..
62. The optical disk for substantially reducing cross-talk
according to claim 58 wherein said track pitch is equal to or less
than 0.81 .lambda..
63. The optical disk for substantially reducing cross-talk
according to any one of claims 60, 61 and 62 wherein said
wavelength is equal to or less than 690 nm.
64. An optical disk for substantially reducing cross-talk during
its input and output operations to and from the optical disks,
comprising: grooves and lands located on the disk for storing data
on both said grooves and said lands, a predetermined distance
between said grooves and said lands being defined as a
predetermined track pitch, wherein said grooves having a depth d in
relation to said lands, wherein said depth is related to a
parameter variable a, a laser wavelength .lambda. which is used
during the operations and a refraction index n of an optical disk
substrate in a relation as (d)>.lambda./(an), wherein said
parameter a ranges from 2.8 to 3.4.
65. The optical disk for substantially reducing cross-talk
according to claim 64 wherein said predetermined track pitch is
equal to or less than 1.1 .lambda..
66. The optical disk for substantially reducing cross-talk
according to claim 64 wherein said track pitch is equal to or less
than 0.96 .lambda..
67. The optical disk for substantially reducing cross-talk
according to claim 64 wherein said track pitch is equal to or less
than 0.81 .lambda..
68. The optical disk for substantially reducing cross-talk
according to any one of claims 65, 66 and 67 wherein said
wavelength is equal to or less than 690 nm.
69. An optical disks for substantially reducing cross-talk during
input and output operations to and from the optical disks,
comprising: grooves and lands located on the disk for storing data
on both said grooves and said lands, a predetermined distance
between said grooves and said lands being defined as a
predetermined track pitch, wherein said grooves having a depth d in
relation to said lands, wherein said depth-is related to parameter
variables a, b and m, a laser wavelength .lambda. which is used
during the operations and a refraction index n of an optical disk
substrate in a relation as d=.lambda./(an)+m.lambda./(bn), wherein
said parameter a satisfies 5.2.ltoreq.a.ltoreq.6.8 while said
parameter b satisfies 1.8.ltoreq.b.ltoreq.2.1, m being a natural
number.
70. The optical disks for substantially reducing cross-talk
according to claim 69 wherein said parameter a satisfies
2.8.ltoreq.a.ltoreq.3.4 while said parameter b satisfies
1.8.ltoreq.b.ltoreq.2.1, m being a positive integer including
0.
71. The optical disks for substantially reducing cross-talk
according to claim 69 wherein said track pitch is equal to or less
than 1.1 .lambda..
72. The optical disks for substantially reducing cross-talk
according to claim 69 wherein said track pitch is equal to or less
than 0.96 .lambda..
73. The optical disks for substantially reducing cross-talk
according to claim 69 wherein said track pitch is equal to or less
than 0.81 .lambda..
74. The optical disks for substantially reducing cross-talk
according to any one of claims 71, 72 and 73 wherein said
wavelength is equal to or less than 690 nm.
75. An optical disks for substantially reducing thermal cross-talk
during input and output operations to and from the optical disks,
comprising: grooves and lands located on the disk, a predetermined
distance between said grooves and said lands being defined as a
predetermined track pitch, wherein said predetermined track pitch
is equal to or less than 1.1 .lambda.where .lambda. is a laser
wavelength used during the operations, said grooves having a depth
d in relation to said lands, wherein said depth is related to a
parameter variable a and a refraction index n of an optical disk
substrate in a relation as d=.lambda./(an).
76. The optical disks according to claim 75 wherein said parameter
a ranges from 2.159 to 3.778.
77. The optical disks according to claim 75 wherein said parameter
a ranges from 2.061 to 3.487.
78. The optical disks according to claim 75 wherein said parameter
a ranges from 2.061 to 3.022.
79. The optical disks according to claim 75 wherein said parameter
a ranges from 1.365 to 1.959.
80. The optical disks according to claim 75 wherein said parameter
a ranges from 0.776 to 1.288.
81. The optical disks according to claim 75 wherein said wavelength
.lambda. is equal to or less than 690 nm.
82. An optical disks for substantially reducing thermal cross-talk
during input and output operations to and from the optical disks,
comprising: grooves and lands located on the disk, a predetermined
distance between said grooves and said lands being defined as a
predetermined track pitch, wherein said predetermined track pitch
is equal to or less than 0.96 .lambda. where .lambda. is a laser
wavelength used during the operations, said grooves having a depth
d in relation to said lands, wherein said depth is related to a
parameter variable a and a refraction index n of an optical disk
substrate in a relation as d=.lambda./(an).
83. The optical disks according to claim 82 wherein said parameter
a ranges from 2.159 to 3.778.
84. The optical disks according to claim 82 wherein said parameter
a ranges from 2.159 to 3.238.
85. The optical disks according to claim 82 wherein said parameter
a ranges from 2.061 to 3.487.
86. The optical disks according to claim 82 wherein said parameter
a ranges from 2.061 to 2.667.
87. The optical disks according to claim 82 wherein said parameter
a ranges from 1.365 to 1.959.
88. The optical disks according to claim 82 wherein said parameter
a ranges from 0.776 to 1.288.
89. The optical disks according to claim 82 wherein said wavelength
.lambda. is equal to or less than 690 nm.
90. An optical disks for substantially reducing thermal cross-talk
during input and output operations to and from t he optical disks,
comprising: grooves and lands located on the disk, a predetermined
distance between said grooves and said lands being defined as a
predetermined track pitch, wherein said predetermined track pitch
is equal to or less than 0.81 .lambda. where .lambda. is a laser
wavelength used during the operations, said grooves having a depth
d in relation to said lands, wherein said depth is related to a
parameter variable a and a refraction index n of an optical disk
substrate in a relation as d=.lambda./(an).
91. The optical disks according to claim 90 wherein said parameter
a ranges from 2.267 to 3.778.
92. The optical disks according to claim 90 wherein said parameter
a ranges from 2.159 to 3.022.
93. The optical disks according to claim 90 wherein said parameter
a ranges from 2.159 to 3.238.
94. The optical disks according to claim 90 wherein said parameter
a ranges from 2.159 to 2.386.
95. The optical disks according to claim 90 wherein said parameter
a ranges from 1.365 to 1.959.
96. The optical disks according to claim 90 wherein said parameter
a ranges from 0.776 to 1.288.
97. The optical disks according to claim 90 wherein said wavelength
.lambda. is equal to less than 690 nm.
98. An optical disks for substantially reducing thermal cross-talk
during input and output operations to and from the optical disks,
comprising: grooves and lands located on the disk, a predetermined
distance between said grooves and said lands being defined as a
predetermined track pitch, wherein said predetermined track pitch
is equal to or less than 1.1 .lambda. where .lambda. is a laser
wavelength used during the operations, said grooves having a depth
d in relation to said lands; wherein said depth is related to a
refraction index n of an optical disk substrate in a relation as
d>.lambda./(4n).
99. The optical disks according to claim 98 wherein said wavelength
.lambda. is equal to or less than 690 nm.
100. The optical disks according to claim 98 wherein said depth d
is selected so as to make I.sub.PP/I.sub.O.gtoreq.0.2.
101. The optical disks according to claim 98 wherein said depth d
is selected so as to make I.sub.G/I.sub.O.gtoreq.0.5.
102. The optical disks according to claim 98 wherein said depth d
is selected so as to make Pe/Pp.gtoreq.1.2.
103. The optical disks according to claim 98 wherein said depth d
is selected so as to make Pe/Pp.gtoreq.1.3.
104. An optical disks for substantially reducing thermal cross-talk
during input and output operations to and from the optical disks,
comprising: grooves and lands located on the disk for storing data
on both said grooves and said lands, a predetermined distance
between said grooves and said lands being defined as a
predetermined track pitch, wherein said predetermined track pitch
is also specified by a predetermined width ratio of said grooves
and said lands, said grooves having a depth d in relation to said
lands, wherein said depth is related to a laser wavelength .lambda.
used during the operations and a refraction index n of an optical
disk substrate in a relation as d>.lambda./(4n).
105. The optical disks according to claim 104 wherein said
wavelength .lambda. is equal to or less than 690 nm.
106. The optical disks according to claim 104 wherein said
predetermined width ratio is larger than 1.
107. The optical disks according to claim 104 wherein said
predetermined width ratio is equal to or larger than 1.05.
108. The optical disks according to claim 104 wherein said
predetermined width ratio is equal to or larger than 1.08.
109. The optical disks according to claim 104 wherein said
predetermined width ratio is equal to or larger than 1.1.
110. The optical disks according to claim 104 wherein said track
pitch is equal to or less than 1.1 .lambda..
111. The optical disks according to claim 104 wherein said track
pitch is equal to or less than 0.96 .lambda..
112. The optical disks according to claim 104 wherein said track
pitch is equal to or less than 0.81 .lambda..
113. The optical disks according to claim 104 wherein said depth d
is selected so as to make Pp(groove)/Pp(land).gtoreq.80.
114. The optical disks according to claim 104 wherein said depth d
is selected so as to make pp(groove)/Pp(land).gtoreq.85.
Description
FIELD OF THE INVENTION
[0001] This invention is generally related to a high density
optical disk and a method of high density recording on an optical
disk. Specifically, it relates to an optical disk which records on
both lands and grooves with a reduced track pitch and the recording
method.
BACKGROUND OF THE INVENTION
[0002] For high speed data processing, high density optical disks
have attracted attention. With the ISO standardization of 5.25-inch
and 3.5-inch disks for optical and phase change schemes for
overwriting, these disks can be expected to have even more
widespread use in the future. Recently, the DVD (digital video
disk) standardization such as SD standardization is about to be
finalized. This standardization is expected to accelerate the use
of optical disks in the area of multi-media.
[0003] In these optical disks, grooves and lands are used to guide
a laser spot emitted from a pickup of a read/write system to the
data. These grooves and lands are formed in a spiral from the
center of the medium to its outer circumference. These grooves are
called guide grooves. More specifically, as defined in the ISO
standard, the recessed portions, which are more distant, as viewed
from the pickup, are referred to as lands, and the raised portions
closer to the pickup, are referred to as grooves.
[0004] Using a land recording method, the groove widths of from
about 0.3 .mu.m to about 0.6 .mu.m, and the groove depths of about
.lambda./8(n) to about .lambda./4(n) wherein .lambda. is the
wavelength of a laser beam used during input and output operations,
and n is a refractive index of substrate. Although the standard
track pitch is 1.6 .mu.m, narrower track pitches are used to
increase the density of the recorded data.
[0005] When using an optical pick up having an object lens of about
0.5 to about 0.6 aperture numerical (NA), the impact of the narrow
track pitch on the undesirable simultaneous reading of data from
adjacent tracks (hereafter referred to as the optical crosstalk)
becomes critical and the tracking error signal is also negatively
affected for accurate tracking.
[0006] For the optical disks currently on the market, the width W
of substrate surface grooves is defined as
W=(W.sub.top+W.sub.bottom)/2, where W.sub.top is the width at the
top of the groove, and W.sub.bottom the width at the bottom. The
groove depth is defined as the height of the substrate surface
groove from the bottom of the groove to the top (step
difference).
[0007] Various methods have been tried in an effort to increase the
recording density of such optical disks, such as making the laser
beam spot smaller by reducing the wavelength of the light source so
as to read data at a higher recording density. There is a limit,
however, in reducing the spot size due to the wavelength of
semiconductor laser that can be used for a light source. In
general, short wavelength laser has problems in forming a desirable
beam shape as well as in an insufficient output level.
[0008] Other efforts to provide a higher recorded data density
resulted in the proposal of a technology called magnetically
induced super-resolution (MSR). This technology is capable of
reading high-density recorded data using a currently available
light source wavelength and a spot size. The MSR technology makes
use of the temperature distribution of the recording medium inside
an area under the light spot (due to a combination of the heating
of the medium by the laser and the rotating motion of the medium)
to mask a portion of the signal on the medium falling under the
light spot so that it will not be detected as the read signal. This
masking makes the effective aperture area from which a signal is
read smaller than the laser spot size, thus making it possible to
read higher density data.
[0009] The Front Aperture Detection (FAD) scheme, which is one way
of implementing the MSR technology, will be briefly described, in
reference to FIG. 2. FIG. 2(a) is a plan view of a FAD-type MSR
disk 31, and FIG. 2(b) is a cross-sectional view of Section I-I of
FIG. 2(a). The FAD optical disk 31 has three magnetic layers: a
recording layer 32, made of TbFeCo; a cutoff layer 33, made of
TbFe; and a readout layer 34, made of GdFeCo. The signal is read
from the readout layer 34. In the initial state as shown in FIG.
2(b), because coupling force is readily exchanged between the
adjacent layers, the orientations of the magnetic field follow the
magnetization of the recording layer 32, which stores the data as
indicated by recording marks 38. During a read operation, an
external magnetic field Hr is applied. When a relative position is
established between a readout light spot 35 and a medium 31, as
shown in FIG. 2(a), a temperature differential is created between a
front low temperature area 36 and a rear high temperature area 37
under the light spot 35.
[0010] When the high temperature area 37 reaches the Curie
temperature at which its magnetization is obliterated of the cutoff
layer 33, the coupling of readout layer 34's magnetization to
recording layer 32 (through cutoff layer 33) is diminished, causing
the magnetization of readout layer 34 to invert to align with the
magnetization of the external magnetic field Hr. In FIG. 2(b), the
magnetized direction of location A is inverted.
[0011] In the high temperature area 37, the magnetization of
readout layer 34 always exhibits a constant state regardless of the
presence of a recording mark 38 and is a mask without contributing
to the readout signal. On the other hand, the signal is detected
only in a low temperature area 36 where its recorded state is
maintained. Thus, the low temperature area 36 serves as an
effective signal detection aperture of the laser spot. This enables
the system to only read recorded mark 38a in the area 36. In this
FAD technique, the masking conditions are determined by the Curie
temperature of the cutoff layer 33. Thus the MSR disks are
manufactured fairly easily by controlling the composition of this
cutoff layer. Techniques other than FAD have been proposed for the
MSR disks. These include Rear Aperture Detection (RAD) and Center
Aperture Detection (CAD), in which the high temperature portion of
the spot is the aperture, and the remaining spot area is masked.
RAD and CAD MSR disks have a smaller aperture because it is the
higher temperature portion of the spot (the temperature
distribution resulting from illumination by the readout laser) that
is an aperture, and the lower temperature portion that is a mask.
In contrast to this, in MSR disks using the FAD technique, the
crescent shape of the aperture (low temperature area 36 within
readout spot 35) renders it impossible to prevent leakage of
signals from adjacent tracks.
[0012] The land-groove recording method has been also proposed for
a high density recording. In contrast to the method in which data
is recorded on either lands or grooves, the land-groove method
increases the recording density to a half track pitch from a full
track pitch by recording data on both lands and grooves. For
example, if the center-to-center distance between adjacent lands
(or grooves) and the next adjacent lands (or grooves) is 1.4 .mu.m,
the proposed land-groove technique increases the data capacity, by
reducing the track pitch to 0.7 .mu.m.
[0013] In this technique, an appropriate groove depth substantially
reduces optical crosstalk or simultaneous data read from adjacent
grooves (or lands). In addition, the center-to-center distance
between lands (or grooves) of 1.4 .mu.m provides a sufficient space
required to maintain for a tracking error signal.
[0014] However, crosserase or heat crosstalk is observed in
recording or erasing information on tracks when the temperature of
the adjacent tracks rises due to the heat from a laser beam. The
higher temperature erases information on the adjacent tracks.
Optical disks and the phase change schemes use thermal recording
technique. In these optical disks, the shorter the distance between
adjacent tracks, the more likely heat travels into adjacent tracks.
Accordingly, it is inevitable for the crosserase problems to
arise.
[0015] As illustrated in FIG. 14, a laser beam is irradiated onto
an optical disk while modulating the peak intensity at Pp to the
bottom intensity at Pb to form marks and to erase the recorded
marks afterwards. To erase the recorded marks, a laser beam is
irradiated onto the optical disk from a DC light source as
illustrated in FIG. 15. At this time the intensity of the laser
beam is determined at Pe. If the marks were originally recorded
with the peak intensity at Pp, the erasure beam intensity of Pe
should be able to erase the marks.
[0016] However, a variety of deviations for recording data
originates from focusing or tracking servo mechanisms, contaminated
lenses, changes in optical properties with time, contaminated
optical disks, and various properties of optical disks due to
temperature, humidity, atmospheric pressure, dust in air, etc. The
intensity of the laser beam fluctuates as these factors change. As
a result of these deviations, a laser beam intensity of Pe at Pp
cannot effectively erase data and requires a greater intensity. In
other words, the various factors mentioned above may increase Pp to
a higher value or decrease Pe to a lower value. In this case, the
recorded marks are recorded as physically larger marks as the
intensity of the laser beam for erasing decreases. Accordingly, the
recorded marks are insufficiently erased to leave a trace of
recorded marks on the disk. This may cause recording and reading
errors.
[0017] The relation between Pe and Pp at the cross-erasure is
measured by the method described below. (1) Set a 130 mm optical
disk having a groove depth of 75 nm and rotate it at a linear
velocity of 9m/sec. This recording reproduction system is equipped
with an optical pickup using the wavelength of 680 nm, NA
(numerical aperture) of 0.55, and the wave front aberration of 0.04
.lambda. (rms value). The system records data on the optical disk
such that both the length of marks and the distance between marks
are 1.2 .mu.m. The bottom intensity Pp of the laser beam is set to
0.8 mW and the recording field is set to 350 Oe. In addition, the
peak intensity Pp is the value showing the minimum level for the
2nd-order harmonic frequency when the recorded marks are read and
the read signals are put into a spectrum analyzer; (2) Next, data
is recorded on a round of land (1 track) on the optical disk such
that both the length of marks and the distance between marks are
0.64 .mu.m while modulating the intensity between the peak
intensity Pp and the bottom intensity Pb of 0.8 mW. The magnetic
field for recording is set to 350 Oe. Then, the recorded marks are
read and the read signals are put into a spectrum analyzer to
measure carrier level. (The initial carrier level is indicated as
Co); (3) Then, a around of groove (1 track) adjacent to the inner
circle of a round of land where the above marks are recorded and
each a round of groove (1 track) adjacent to the outer circle are
erased for 10 spinnings at Pe, the laser beam intensity erasing as
illustrated in FIG. 7; (4) Next, the land on which marks are
recorded is reproduced and the reproduced signals are put into a
spectrum analyzer to measure a carrier level. (After cross-erasure,
carrier level is indicated as Ce); (5) Change the Pe value. Repeat
(3) to (4) until Co-Ce=0.5. Obtain Pe/Pp at that time. Then, Pe/Pp
is obtained in the same manner as described in the above from (1)
to (5) for erasing lands adjacent to recorded grooves.
[0018] In the conventional optical disk with guide grooves, the
heat crosstalk determines the track pitch. The track pitch for the
conventional optical and phase change type disks is limited to
about 0.8 .mu.m. The track pitch for the optically modulated
overwritable optical type is limited to about 0.9 .mu.m or about
1.0 .mu.m. A narrower track than the above mentioned dimension had
been considered impractical.
[0019] Since the performance of an optical disk is dependent on not
only the heat crosstalk but also noise from the substrate, it had
been difficult in prior art to manufacture an optical disk without
the above-described two undesirable effects.
[0020] Prior art teaches a technique to increase the groove depth
in order to reduce thermal crosstalk. In other words, increasing
the groove depth increases the distance heat propagates before
reaching the adjacent tracks so as to reduce the undesirable effect
of heat. For example, Japanese patent 6-223421 discloses that when
the groove depth is increased up to 130-280 nm from a conventional
range from about 40 to about 90 nm, the track pitch can be
narrowed.
[0021] This does not mean that any depth of 100 nm or more is
acceptable. First, the preferable land or groove reflection
coefficient of is 0.5 or more in order to maintain a desirable read
signal level. However, the land or groove reflection coefficients
vary based on the groove depth. Some groove depth values even lower
the readout signal level, causing a data readout error. In
addition, although a preferable push-pull signal modulation factor
is larger than 0.2 in order to maintain an accurate tracking
capability, some groove depth values lower the push-pull signal
modulation factor to cause mistracking, slow access, and erroneous
erasure.
[0022] The current invention is directed to resolve the above and
other described problems and to provide an optical disk having
reduced thermal crosstalk and noise from the substrate. In
addition, this invention is directed to a method of reading and
recording high-density data on an optical disk.
SUMMARY OF THE INVENTION
[0023] In order to solve the above and other problems, according to
one method of manufacturing optical disks for substantially
reducing cross-talk during input and output operations to and from
the optical disks each having grooves and lands, data being stored
on both the grooves and lands, the method includes the steps of: a)
specifying a track pitch between the grooves and the lands; b)
selecting a depth of the grooves d in relation to the lands to
satisfy a first relation, d=.lambda./(an) where a is a parameter
variable, .lambda. is a laser wavelength used during the operations
and n is a refraction index of an optical disk substrate; and c)
further selecting the depth d so as to make the cross-talk equal to
or less than -25 dB while the first relation in the step b) is
maintained.
[0024] According to a second aspect of the current invention, a
method of manufacturing optical disks for substantially reducing
cross-talk during input and output operations to and from the
optical disks each having grooves and lands, data being stored on
both the grooves and lands, includes the steps of: a) specifying a
track pitch between the grooves and the lands; and b) selecting a
depth of the grooves d in relation to the lands to satisfy a first
relation, d=.lambda./(an) where a is a parameter variable, .lambda.
is a laser wavelength used during the operations and n is a
refraction index of an optical disk substrate, the parameter ranges
from 2.8 to 3.4.
[0025] According to a third aspect of the current invention, a
method of manufacturing optical disks for substantially reducing
cross-talk during input and output operations to and from the
optical disks each having grooves and lands, data being stored on
both the grooves and lands, includes the steps of: a) specifying a
track pitch between the grooves and the lands; b) selecting a depth
of the grooves d in relation to the lands to satisfy a first
relation, d=.lambda./(an)+m.lambda./(bn) where a and b are
parameter variables, .lambda. is a laser wavelength used during the
operations, m is an integer and n is a refraction index of an
optical disk substrate, wherein the parameter a satisfies
5.2.ltoreq.a.ltoreq.6.8 while the parameter b satisfies
1.8.ltoreq.b.ltoreq.2.1, m being a natural number.
[0026] According to a fourth aspect of the current invention, a
method of manufacturing optical disks for substantially reducing
thermal cross-talk during input and output operations to and from
the optical disks each having grooves and lands including the steps
of: a) specifying a track pitch between the grooves and the lands
to be equal or less than 1.1 .lambda. where .lambda. is a laser
wavelength used during the operations; and b) selecting a depth of
the grooves d in relation to the lands to satisfy a first relation,
d=.lambda./(an) where a is a parameter variable and n is a
refraction index of an optical disk substrate.
[0027] According to a fifth aspect of the current invention, a
method of manufacturing optical disks for substantially reducing
thermal cross-talk during input and output operations to and from
the optical disks each having grooves and lands incudes the steps
of: a) specifying a track pitch between the grooves and the lands
to be equal or less than 0.96 .lambda. where .lambda. is a laser
wavelength used during the operations; and b) selecting a depth of
the grooves d in relation to the lands to satisfy a first relation,
d=.lambda./(an) where a is a parameter variable and n is a
refraction index of an optical disk substrate.
[0028] According to a sixth aspect of the current invention, a
method of manufacturing optical disks for substantially reducing
thermal cross-talk during input and output operations to and from
the optical disks each having grooves and lands comprising the
steps of: a) specifying a track pitch between the grooves and the
lands to be equal or less than 0.81 .lambda. where .lambda. is a
laser wavelength used during the operations; and b) selecting a
depth of the grooves d in relation to the lands to satisfy a first
relation, d=.lambda./(an) where a is a parameter variable and n is
a refraction index of an optical disk substrate.
[0029] According to a seventh aspect of the current invention, a
method of manufacturing optical disks for substantially reducing
thermal cross-talk during input and output operations to and from
the optical disks each having grooves and lands comprising the
steps of: a) specifying a track pitch between the grooves and the
lands to be equal or less than 1.1 .lambda. where .lambda. is a
laser wavelength used during the operations; and b) selecting a
depth of the grooves d in relation to the lands to satisfy a first
relation, d>.lambda./(4n) where n is a refraction index of an
optical disk substrate.
[0030] According to an eighth aspect of the current invention, a
method of manufacturing optical disks for substantially reducing
thermal cross-talk during input and output operations to and from
the optical disks each having grooves and lands, data being stored
on both the grooves and lands, including the steps of: a)
specifying a track pitch between the grooves and the lands at a
predetermined width ratio of the grooves and the lands; and b)
selecting a depth of the grooves d in relation to the lands to
satisfy a first relation, d>.lambda./(4n) where .lambda. is a
laser wavelength used during the operations and n is a refraction
index of an optical disk substrate.
[0031] According to a ninth aspect of the current invention, an
optical disk for substantially reducing cross-talk during its input
and output operations to and from the optical disks, includes:
grooves and lands located on the disk for storing data on both the
grooves and the lands, a predetermined distance between the grooves
and the lands being defined as a predetermined track pitch, wherein
the grooves having a depth d in relation to the lands, wherein the
depth is related to a parameter variable a, a laser wavelength
.lambda. which is used during the operations and a refraction index
n of an optical disk substrate in a relation as
(d)>.lambda./(an), the depth d is further determined so that
cross-talk is equal to or less than -25 dB while the relation is
maintained.
[0032] According to a tenth aspect of the current invention, an
optical disk for substantially reducing cross-talk during its input
and output operations to and from the optical disks, including:
grooves and lands located on the disk for storing data on both the
grooves and the lands, a predetermined distance between the grooves
and the lands being defined as a predetermined track pitch, wherein
the grooves having a depth d in relation to the lands, wherein the
depth is related to a parameter variable a, a laser wavelength
.lambda. which is used during the operations and a refraction index
n of an optical disk substrate in a relation as
(d)>.lambda./(an), wherein the parameter a ranges from 2.8 to
3.4.
[0033] According to an eleventh aspect of the current invention, an
optical disks for substantially reducing cross-talk during input
and output operations to and from the optical disks, including:
grooves and lands located on the disk for storing data on both the
grooves and the lands, a predetermined distance between the grooves
and the lands being defined as a predetermined track pitch, wherein
the grooves having a depth d in relation to the lands, wherein the
depth is related to parameter variables a, b and m, a laser
wavelength .lambda. which is used during the operations and a
refraction index n of an optical disk substrate in a relation as
d=.lambda./(an)+m.lambda./(bn), wherein the parameter a satisfies
5.2 s a s 6.8 while the parameter b satisfies
1.8.ltoreq.b.ltoreq.2.1, m being a natural number.
[0034] According to a twelfth aspect of the current invention, an
optical disks for substantially reducing thermal cross-talk during
input and output operations to and from the optical disks,
including: grooves and lands located on the disk, a predetermined
distance between the grooves and the lands being defined as a
predetermined track pitch, wherein the predetermined track pitch is
equal to or less than 1.1 .lambda. where .lambda. is a laser
wavelength used during the operations, the grooves having a depth d
in relation to the lands, wherein the depth is related to a
parameter variable a and a refraction index n of an optical disk
substrate in a relation as d=.lambda./(an).
[0035] According to a thirteenth aspect of the current invention,
an optical disks for substantially reducing thermal cross-talk
during input and output operations to and from the optical disks,
including: grooves and lands located on the disk, a predetermined
distance between the grooves and the lands being defined as a
predetermined track pitch, wherein the predetermined track pitch is
equal to or less than 0.96 .lambda. where .lambda. is a laser
wavelength used during the operations, the grooves having a depth d
in relation to the lands, wherein the depth is related to a
parameter variable a and a refraction index n of an optical disk
substrate in a relation as d=.lambda./(an).
[0036] According to a fourteenth aspect of the current invention,
an optical disks for substantially reducing thermal cross-talk
during input and output operations to and from the optical disks,
including: grooves and lands located on the disk, a predetermined
distance between the grooves and the lands being defined as a
predetermined track pitch, wherein the predetermined track pitch is
equal to or less than 0.81 .lambda. where .lambda. is a laser
wavelength used during the operations, the grooves having a depth d
in relation to the lands, wherein the depth is related to a
parameter variable a and a refraction index n of an optical disk
substrate in a relation as d=.lambda./(an).
[0037] According to a fifteenth aspect of the current invention,
optical disks for substantially reducing thermal cross-talk during
input and output operations to and from the optical disks,
including: grooves and lands located on the disk, a predetermined
distance between the grooves and the lands being defined as a
predetermined track pitch, wherein the predetermined track pitch is
equal to or less than 1.1 .lambda. where .lambda. is a laser
wavelength used during the operations, the grooves having a depth d
in relation to the lands, wherein the depth is related to a
refraction index n of an optical disk substrate in a relation as
d>.lambda./(4n).
[0038] According to a sixteenth aspect of the current invention, an
optical disks for substantially reducing thermal cross-talk during
input and output operations to and from the optical disks,
including: grooves and lands located on the disk for storing data
on both the grooves and the lands, a predetermined distance between
the grooves and the lands being defined as a predetermined track
pitch, wherein the predetermined track pitch is also specified by a
predetermined width ratio of the grooves and the lands, the grooves
having a depth d in relation to the lands, wherein the depth is
related to a laser wavelength x used during the operations and a
refraction index n of an optical disk substrate in a relation as
d>.lambda./(4n).
BRIEF DESCRIPTION OF DRAWINGS
[0039] FIG. 1(a) is a diagram showing an optical disk according to
the current invention.
[0040] FIG. 1(b) is an enlarged cross-sectional view of the optical
disk taken at A-A in FIG. 1(a).
[0041] FIG. 2(a) is a top view of a FAD-type optical disk which is
one form of an MSR disk.
[0042] FIG. 2(b) shows a cross-section view taken at I-I of a
FAD-type optical disk of FIG. 2(a).
[0043] FIG. 3 illustrates how heat travels to the adjacent track
through the side walls of the grooves.
[0044] FIG. 4 is a plot showing cross-erasure measurement values in
relation to the groove depth.
[0045] FIG. 5 shows readout signal carrier level and signal
crosstalk values in relation to the groove depth.
[0046] FIG. 6 illustrates a relation between a cross-erasure amount
in dB and the groove depth amount.
[0047] FIG. 7 illustrates a relation between a noise amount in dB
and the groove depth.
[0048] FIG. 8 is a graph showing the relation between the groove
depth and I.sub.G/I.sub.O and I.sub.PP/I.sub.O during a data read
operation using H polarization from an optical disk having both a
land width and a groove width of 0.7 .mu.m.
[0049] FIG. 9 is a graph showing the relation between the groove
depth and I.sub.G/I.sub.O and I.sub.PP/I.sub.O during data read
operation using H polarization from an optical disk having both a
land width and groove width of 0.6 .mu.m.
[0050] FIG. 10 is a graph showing the relation between the groove
depth and I.sub.G/I.sub.O and I.sub.PP/I.sub.O during data read
operation using H polarization from an optical disk having both a
land width and groove width of 0.5 .mu.m.
[0051] FIG. 11 is a graph showing the relation between the groove
depth and I.sub.G/I.sub.O and I.sub.PP/I.sub.O during data read
operation using E polarization from an optical disk having both a
land width and groove width of 0.7 .mu.m.
[0052] FIG. 12 is a graph showing the relation between the groove
depth and I.sub.G/I.sub.O and I.sub.PP/I.sub.O during data read
operation using E polarization from an optical disk having both a
land width and groove width of 0.6 .mu.m.
[0053] FIG. 13 is a graph showing the relation between the groove
depth and I.sub.G/I.sub.O and I.sub.PP/I.sub.O during data read
operation using E polarization from an optical disk having both a
land width and groove width of 0.5 .mu.m.
[0054] FIG. 14 is a diagram showing a laser beam intensity wave
profile modulated for date recording.
[0055] FIG. 15 is a diagram illustrating the laser beam DC profile
for erasure.
[0056] FIG. 16 is a graph showing the optimal data recording peak
power for the land and groove width ratios of an optical disk of
the current invention wherein the groove depth is 280 nm.
[0057] FIG. 17 is a graph showing the optimal data recording peak
power for the land and groove width ratios of an optical disk of
the current invention wherein the groove depth is 140 nm.
[0058] FIG. 18 is a graph showing the optimal data recording peak
power for the land and groove width ratios of an optical disk of
the current invention wherein the groove depth is 190 nm.
[0059] FIG. 19 is a graph showing the optimal data recording peak
power for the land and groove width ratios of an optical disk of
the current invention wherein the groove depth is 550 nm.
[0060] FIG. 20 is a diagram showing the laser driving wave profile
during data recording.
[0061] FIG. 21 is a graph showing the optimal data recording peak
power for the land and groove width ratios of a conventional
optical disk wherein the groove depth is 48 nm.
DETAILED DESCRIPTIONS OF PREFERRED EMBODIMENTS
[0062] FIG. 1(a) shows an oblique top view of one preferred
embodiment of an optical disk 1 according to the present invention,
and FIG. 1(b) is an enlarged cross-sectional view of a portion
taken at A-A of the optical disk shown in FIG. 1(a). FIG. 1(b)
shows a transparent substrate 2 with lands 5 and grooves 6, which
respectively appear as recesses and protrusions when viewed from an
optical pickup side of the disk. Although the optical pickup is not
shown, it is located at the bottom in FIG. 1(b). Still referring to
FIG. 1(b), a base layer 3 is made of SiN and formed on the
substrate 2, while a recording layer 4 is formed on the base layer
3. Omitted from FIG. 1(b) is a protective layer formed on recording
layer 4.
[0063] Next, a method of manufacturing an optical disk 1 will be
described. According to one preferred method, an example of
manufacturing a FAD-type MSR optical disk is described. First, a
stamper and a glass substrate are provided so as to inject UV-cure
resin between the stamper and the substrate. The 2P ultra-violet
irradiation cure process is performed to harden the resin. This
forms a 3.5-inch guide-grooved transparent resin substrate 2,
having lands 5 and grooves 6 on the glass substrate. The width of
both the lands 5 and the grooves 6 is each 0.6 .mu.m. As an
alternative, injection molding is used with the stamper to
fabricate a similar guide-grooved plastic substrate 2. Next, a base
layer 3 of SiN is formed on the guide-grooved substrate 2 by a
sputtering process. Then, a recording layer 4 is formed on the base
layer 3 by sequentially sputtering a GdFeCo film layer (readout
layer 34 of FIG. 2), a TbFe film layer (a cutoff layer 33), and a
TbFeCo film layer (a recording layer 32). The fabrication of the
optical disk is then completed by similarly forming a protective
layer of SiN (not illustrated) on this recording layer 4.
[0064] Using the above manufacturing method, a number of optical
disks having a guide-grooved substrate 2 with different groove
depths (i.e., changing the depth d of groove 6) were fabricated. As
shown in FIG. 3, the elongated depth provides a longer distance for
heat to travel to reach an adjacent track. Each of these optical
disks was placed in a recording system and marks (data) were
recorded in the lands or grooves. Cross-erasure was measured using
an optical pickup with a readout light wavelength 1 of 680 nm, an
objective lens numerical aperture (NA) value of 0.55, and wavefront
aberration of 0.025 .lambda. (rms) while the substrate was spinning
at 2400 rpm. The direction of polarization at normal incidence was
parallel to the grooves, and this direction was referred to as E
polarization.
[0065] The above-described cross-erasure measurements are
summarized in a graph as shown in FIG. 4. If a land or a groove on
the disk is defined to be a first track, an adjacent land or groove
is defined to be a second track. In other words, the second track
is a groove if the first track is a land. Similarly, the second
track is a land if the first track is a groove. Based upon the
above definition, cross erasure is a phenomenon wherein the
boundary portions of marks recorded in the first track are erased
by thermal interference from the second track when recording or
erasing is performed on the second track.
[0066] The cross-erasure margin plotted in FIG. 4 is the ratio
P.sub.e/P.sub.P, where P.sub.P is the first track record power (the
power of the laser beam for recording marks in the first track),
and P.sub.e is a laser beam power at which the second track is
recorded or erased to cause the marks recorded in the first track
to be erased, and to cause the first track carrier level to be
reduced. A large cross-erasure margin generally indicates a greater
margin for the first track with respect to P2 when the power of the
laser being directed at the second track. In other words, a greater
margin means reduced susceptibility to cross-erasure.
[0067] Still referring to FIG. 4, the cross-erasure or thermal
crosstalk is reduced by increasing d, the depth of the grooves.
That is, the groove step size or groove depth should be made
greater to increase the thermal propagation distance to an adjacent
track.
[0068] FIG. 5 shows one example of calculated values for readout
signal carrier levels and crosstalk under .lambda.=180 .mu.m,
NA=0.55, the groove depth -0.025.lambda., M=1.5. Carrier level is
indicated by a curve C while crosstalk is indicated by a curve CT.
The carrier level values shown here are values relative to a signal
written to a mirror surface as the reference level. The crosstalk
values are the difference between the short mark carrier level and
the long mark carrier level when the short marks are recorded on a
single track which has adjacent tracks on both sides where the long
marks are recorded.
[0069] Still referring to FIG. 5, while there is less than 10 dB
variation in the carrier level over the groove depth ranging from 0
to 400 nm, there is an approximately 40 dB variation in crosstalk
over the same range. The signal crosstalk is thus reduced at
certain groove depths. Three groove depths d greater than 100 nm
around 150 nm, 310 nm, and 370 nm at which the crosstalk signal has
the least values.
[0070] According to the manufacturing method described earlier,
optical disks are fabricated with groove depths d at 150 nm, 310
nm, and 370 nm. Table 1 shows the signal C/N (carrier-to-noise)
ratios and signal crosstalk measurements of the above-described
optical disks.
1TABLE 1 Groove Depth d C/N (dB) Crosstalk (dB) (nm) Land Groove
Land Groove 150 43.0 42.0 -38.0 -36.5 310 42.0 42.5 -30.5 -29.0 370
42.0 41.5 -28.0 -28.5
[0071] The record/read system described earlier was used to record
0.4 .mu.m-long marks on the disk located at a radius of 35 mm,
while applying a 500 Oe magnetic field (the external field Hr of
FIG. 2). The C/N values in Table 1 are measured while the recorded
marks were read back using a readout power of 3.0 mW. To measure a
crosstalk signal, 0.4 .mu.m-long marks were recorded on a first
track, and 1.6 .mu.m-long marks were recorded on second tracks
adjacent to the first track. The first track was then read, and the
difference between the 0.4 .mu.m mark carrier level and the 1.6
.mu.m mark carrier level which leaked from the second tracks was
measured as a crosstalk signal. From Table 1, according to one
preferred method, the depth d is selected to substantially reduce
crosstalk less than -25 dB.
[0072] For comparison, a group of optical disks having a groove
depth d at 200 nm and 350 nm was fabricated. Table 2 lists the same
measurements taken from these disks.
2TABLE 2 Groove Depth d C/N (dB) Crosstalk (dB) (nm) Land Groove
Land Groove 200 45.5 45.0 -8.5 -7.0 350 42.0 41.5 -16.0 -17.5
[0073] From the above table, it was seen that the results of actual
measurements as listed in Tables 1 and 2 are compatible with the
computed results of FIG. 5. Based on FIG. 5, in order to realize
signal crosstalk levels below -25 dB, groove depth should be set
within a range of 137 nm-162 nm, 282nm -326 nm or 364 nm-389
nm.
[0074] Note that the characteristics in FIG. 5 are obtained with a
readout laser light wavelength .lambda. of 680 nm and a
guide-grooved substrate refractive index n of 1.5. Changes in these
parameters change the groove depths at which the above-specified
minimum crosstalk is obtained. However, in general, the light
wavelength of less then 690 nm.
[0075] From the foregoing, the depth d of the grooves should
preferably satisfy the following equation:
d=.lambda./(a.times.n)+m.times..lambda./(b.times.n)
[0076] where a, m and b are parameters, .lambda. is a wavelength of
laser beam, n is a refractive index of a substrate. m, a, and b for
the first peaks satisfy the relations
[0077] m=1, 2, 3 . . . ,
[0078] 5.2.ltoreq.a.ltoreq.6.8, and
[0079] 1.8.ltoreq.b.ltoreq.2.1
[0080] and m, a, and b for the second peaks satisfy the
relations
[0081] m=0, 1, 2, 3 . . . ,
[0082] 2.8.ltoreq.a.ltoreq.3.4, and
[0083] 1.8.ltoreq.b.ltoreq.2.1
[0084] The track pitch is preferably equal to or less than 1.1
.lambda., 0.96 .lambda., or 0.81 .lambda..
[0085] In the alternative, the condition d=.lambda./(an) where a is
a parameter, .lambda. is a laser beam wavelength, and n is
refractive index. The parameter a ranges from 2.8 to 3.4.
[0086] Although the present embodiment was described for FAD-type
MSR optical disks, the present invention is not dependent upon the
films formed groove on guided substrate 2. Therefore, similar
results are obtained by the present invention using other types of
MSR optical disks. Similar results are also obtained by the present
invention using conventional non-MSR optical disks. In fact,
similar results are realized by the present invention using phase
change-type optical disks.
EXAMPLES OF EMBODIMENTS
[0087] Embodiment 1
[0088] A plurality of optical disk substrates having a variety of
land-groove groove depth or groove depths were prepared. The width
of both lands and grooves for these optical disk substrates is 0.7
.mu.m, and their groove depths are from about 50 nm to about 400
nm. These substrates were sputtered with a SiN protective layer 70
nm thick, an optical recording TbFeCo layer 50 nm thick, and a SiN
protective layer 70 nm thick in this order to produce the optical
disk.
[0089] These optical disks were set in a record/readout system.
This record/readout system has an optical head using a
semiconductor laser of 680 nm wavelength and an optical head using
a lens system of NA 0.55. After a recording mark was recorded in a
measurement track, it was erased 100 times by tracking the
measurement track by offsetting 0.05 .mu.m toward the adjacent
track; the amount of change in the cross erasing on the recording
mark recorded on the measurement track was measured. The amount of
change in the cross erasing is illustrated in FIG. 6. FIG. 6 shows
that the thermal crosstalk phenomena was substantially eliminated
when the groove depth was over 100 nm.
[0090] Embodiment 2
[0091] The measurements were taken in the same manner for disks
with the land and groove width each at 0.6 .mu.m. The measurements
are shown it FIG. 6. According to FIG. 6, thermal heat crosstalk is
substantially eliminated at the groove depth of over 150 nm.
[0092] In addition, noise caused by the condition of the substrate
was measured. Referring to FIG. 7, the measurement resulted from a
substrate having the land and groove width of 0.6 .mu.m. According
to FIG. 7, noise significantly increases when the groove depth is
equal to or greater than 300 nm.
[0093] The groove depth ranging from about 100 nm to about 300 nm
is preferred since the noise level from the substrate is minimized.
Also, in the optical disk, at a narrow track pitch around the land
and groove width of 0.6 .mu.m, the preferred groove depth ranges
from about 150 nm to about 300 nm.
[0094] Embodiment Set 1
[0095] Prepare a plurality of optical disks at a track pitch of 0.7
.mu.m, 0.6 .mu.m, and 0.5 .mu.m having the following 29 different
groove depth between lands and grooves. The 29 groove depth
include: 40, 60, 80, 100, 120, 140, 160, 180, 200, 220, 240, 260,
280, 300, 320, 340, 360, 380, 400, 420, 440, 460, 480, 500, 520,
540, 560, 580 and 600.
[0096] After placing these optical disks in a record/readout
system, the reflection coefficient and the push-pull signal
modulation factor in the grooves are measured. The base values
I.sub.G/I.sub.O and I.sub.PP/I.sub.O are derived from the
reflection coefficient I.sub.o which is taken from the region where
there are no guided grooves. The optical pickup in the
record/readout system uses a laser beam with the wavelength
.lambda. of 680 nm, objective lens NA of 0.55, and wavefront
aberration 0.04 .lambda. (rms value). The directions of linear
polarization at normal incident for an optical disk is selected
parallel (referred to as E polarization) or perpendicular to the
grooves (referred to as H polarization).
[0097] FIG. 8 is a graph showing I.sub.G/I.sub.O and
I.sub.PP/I.sub.O during a read operation using H polarization from
an optical disk having both the land width and the groove width of
0.7 .mu.m. I.sub.PP is a push-pull signal while I.sub.G of I.sub.L
is an on-track signal. FIG. 9 shows I.sub.G/I.sub.O and
I.sub.PP/I.sub.O during a read operation using H polarization from
an optical disk having both the land width and the groove width of
0.6 .mu.m; FIG. 10 shows I.sub.G/I.sub.O and I.sub.PP/I.sub.O
during a read operation using H polarization from a optical disk
having both a land width and groove width of 0.5 .mu.m. Also, FIG.
11 is a graph showing I.sub.G/I.sub.O and I.sub.PP/I.sub.O during a
read operation using E polarization from an optical disk having
both the land width and the groove width of 0.7 .mu.m; FIG. 12
shows I.sub.G/I.sub.O and I.sub.PP/I.sub.O during a read operation
using E polarization from an optical disk having both the land
width and the groove width of 0.6 .mu.m; FIG. 13 shows
I.sub.G/I.sub.O and I.sub.PP/I.sub.O during a read operation using
E polarization from an optical disk having both the land width and
the groove width of 0.5 .mu.m. Note that the reflection coefficient
of lands (I.sub.L/I.sub.O) is nearly equal or proportional to that
of the grooves I.sub.L/I.sub.O, showing the same orientation.
[0098] It is preferable that the groove reflection coefficient
I.sub.G/I.sub.O be 0.5 or larger in order to obtain a desirable
readout signal level. Also, it is preferable that the push-pull
signal modulation level I.sub.PP/I.sub.O be 0.2 or larger in order
to obtain an accurate tracking capability.
[0099] In this view, it is apparent from FIGS. 8 through 13 that
the preferable groove depth ranges from about 110 nm to about 220
nm, from about 230 nm to about 330 nm, or from about 350 nm to
about 580 nm. In addition, when reading under H polarization, in
comparison to the result obtained from E polarization, the
reflection coefficient value of grooves is larger, facilitating to
obtain a good read signal level. When reading in H polarization, a
desirable result is obtained when the groove depth ranges from
about 110 to about 210 nm, about 230 to about 320 nm, about 350 to
about 440 nm, or about 450 to about 570 nm. In addition, the groove
depth of 530 nm or larger substantially reduces thermal crosstalk
for the track pitch of as narrow as 0.3 .mu.m.
[0100] At the track pitch equal to or less than 1.1 .lambda., the
parameter a in d>.lambda./(an) ranges from 2.159 to 3.778, from
2.061 to 3.487, or from 2.061 to 3.022. At the track pitch equal to
or less than 0.96 .lambda., the parameter a ranges from 2.159 to
3.778, from 2.159 to 3.238, from 2.061 to 3.487 or from 2.061 to
2.667. At the track pitch equal to or less than 0.81, the parameter
a ranges from 2.267 to 3.778, from 2.159 to 3.022, from 2.159 to
3.238 or from 2.159 to 2.386.
[0101] In summary, the above described preferred embodiments of the
current invention enable optical disks to operate at a high density
without sacrificing a readout signal level and highly accurate
tracking.
[0102] Embodiment Set 2
[0103] Preferred embodiments of the overwritable optic disks
include: Guide-grooved transmittive substrate; Si.sub.3N.sub.4
Layer; GdFeCo layer (Gd 23%, Fe 65%, Co 12% (atom %)); TbFeCo layer
(Th 20%, Fe 76%, Co 4%); GdFeCo layer (Gd 24%, Fe 72.2%, Co 3.8%);
DyFeCo layer (Dy 26%, Fe 48.1%, Co 25.9%); TbFeCo layer (Tb 17%, Fe
77%, Co 6%); TbFeCo layer (Tb 23%, Fe 15.4%, Co 61.6%);
Si.sub.3N.sub.4 layer; Al layer and organic protective layer. As
described for the Embodiment Set 1, 29 different groove depths are
manufactured in Embodiment Set 2.
[0104] After placing the above overwritable optical disks in a
record/readout system, the reflection coefficient and the push-pull
signal modulation factor in grooves are measured in the same manner
as measured from Embodiment Set 1. The results are substantially
the same as those obtained in Embodiment Set 1 as shown in FIGS. 8
through 13. In other words, the preferred groove depth is from
about 110 to about 220 nm, from about 230 to about 330 nm, or from
about 350 to about 580 nm. In addition, when reading under the H
polarization, in comparison to the result obtained under the E
polarization, the reflection coefficient value of grooves is larger
to facilitate a desirable read signal level. Also reading under the
H polarization, a desirable result is obtained when the groove
depth is from about 110 to about 210 nm, from about 230 to about
320 nm, from about 350 to about 440 .mu.m, or from about 450 to
about 570 nm.
[0105] A read signal level is maximized at the groove depth of
m.lambda./(2n) where the beam spot wave length is .lambda. and the
refractive index of an optical disk substrate is n. Note that m is
a natural number (m=1, 2, 3, 4, 5, 6, . . . ) For example, when
.lambda.=680 nm, n=1.5, and m=1, the maximum readout signal is
obtained at the groove depth of 226.7 nm. Other two parameters
being equal, when m=2, it is 453.3 nm while m=3, it is 680 nm. In
reality, due to the direction of polarization and the like, it is
not precisely m.lambda./(2n) but may be, for example,
m.lambda./(1.8n) or m.lambda./(1.95n) for reading under a normal
polarization having the polarized surface parallel to the guided
grooves. The push-pull signal modulation factor is maximized at the
groove depth of (2m+1) .lambda./(8n).
[0106] The increased groove depth on a conventional optical disk
makes it difficult to manufacture a protective layer or optical
recording layer in grooves that are recessed portions of the
substrate surface. This is because the groove portion is hidden
behind the land portion, and the substance for an optical recording
layer is substantially prevented from reaching the grooves. For the
manufacture of the disks using the sputtering method, this
phenomenon is prominent. This problem does not occur in the land
portion. As a result, the film thickness in the groove portion is
thinner than that in the land portion. This problem is prominent at
the edges of grooves near the land-groove boundary.
[0107] Since the film thicknesses are not uniform over the groove
and land portions, the optimal data recording beam intensity for
the groove potion needs to be adjusted from that for the land
portion. In other words, the optimal data recording beam intensity
for the groove portion needs to be lower than that for the land
portion. However, if data is recorded in grooves using the same
value which is the optimal data recording beam intensity for the
land portion, the beam energy is too strong for the optimal data
recording beam intensity in the groove portion. Consequently, the
length of the recording mark is undesirably longer than a
predetermined desirable length, and the elongated recording marks
likely cause an erroneous data read operation. On the other hand,
if data is recorded in lands using the same value which is the
optimal data recording beam intensity for the groove portion, the
beam energy is too weak for the optimal data recording beam
intensity in the groove portion. Again as a consequence, since the
length of the recording mark is shorter than a predetermined
desirable length, a data read error is likely to be resulted.
[0108] The above phenomena affect not only the film thickness but
also the composition of an optical data recording layer. This is
because each element which constitutes the optical data recording
layer substance behaves differently during manufacture, and the
shadow created by the land portion affects each element.
[0109] When the composition of an optical data recording layer
deviates from a predetermined composition, magnetic properties also
change and possibly interfere with the desired functions. As a
result, one may encounter problems such as increased data recording
errors in either lands or grooves, or in worse cases, one may not
be able to record.
[0110] The above described manufacturing problem impacts optical
data storage media of the magnetically induced super resolution
(MSR) and direct overwrite (DOW) type even more seriously than
those of an ordinary type because the above disks each includes
multiple optical data storage layers.
[0111] The current invention resolves the above problems and to
provide an optical disk of excellent reliability with a uniform
property in lands and grooves. It also provides a method of
recording using such optical disks. The current invention assumes
the groove depth of equal to or greater than .lambda./4n and
applies a wider width for grooves than lands to resolve the above
problems.
[0112] Embodiment Set 3
[0113] According to one preferred method of the current invention,
two types of optical disks whose sum of the land width and the
groove width is 1.4 .mu.m or 1.2 .mu.m with the groove depth of 140
nm, 190 nm, 280 nm, and 550 nm. Optical disks having nine (groove
width/land width) ratios such as 1, 1.05, 1.08, 1.1, 1.15, 1.2,
1.3, 1.5, and 2 satisfy the above sum requirement. Note that these
optical disks are manufactured by sequentially sputtering a SiN
layer, a TbFeCo optical data storage layer, and SiN layer on a
substrate.
[0114] The optical pickup in the optical disk drive has the light
source wave length of 680 nm, objective lens numerical aperture
(NA) aperture of 0.55, and the wavefront aberration of 0.04 (rms
value). The direction of polarization of a beam emitted from the
optical pick up is parallel in respect to the guide-grooved
substrate, that is, E-polarization. After placing the
above-described optical disks in the optical disk drive, the disks
were rotated at a linear velocity of 9 m/sec., and the optimal data
recording peak power of Pp in lands and grooves was measured. The
optimal data recording peak power was defined as the minimum
distortion level for the 2nd-order harmonic frequency when the
recording marks are reproduced, and the reproduced signals are
inputted to a spectrum analyzer. The laser driving wave profile at
this time is illustrated in FIG. 20 in which the length of the
recording mark is set to 1.2 .mu.m and the space between the
recording marks is also set to 1.2 .mu.m. In addition, the data
recording bottom power Pb is set to 0.8 mW, and the data recording
magnetic field intensity is set to 350 Oe at which no mark is
recorded.
[0115] The measurements are plotted in FIGS. 16 through 19 for only
those optical disks whose sum of the land width and the groove
width is 1.4 .mu.m, and the measurement for disks whose sum was 1.2
.mu.m were substantially the same. FIG. 16 plots the measurements
for optical disks whose groove depth is 280 nm. FIG. 17 plots the
measurements for optical disks whose groove depth is 140 nm.
Similarly, FIG. 18 plots the measurements for the optical disks
with 190 nm step. While FIG. 19 plots the measurements for the one
with 550 nm step. In contrast, FIG. 21 plots the measurements for
conventional optical disks with the groove depth of 48 nm.
[0116] According to the above plots, if an optical disk has the
groove/land width ratio of 1.05 or more, the disk functions well
with the groove depth of equal to or greater than 140 nm. If the
ratio is 1.2 or more, the groove depth of equal to or greater than
280 nm is desired. In addition, if the value is 1.3 or larger, the
groove depth of at least 550 nm is necessary for the desirable
effect.
[0117] However, to use a common sputtering method other than
special sputtering methods or special fabrication methods, the
groove/land width ratio needs to be even greater. In some cases,
the preferable ratio is 1.3, 1.4 or larger.
[0118] In summary, according to the current invention, by widening
the groove width of optical disks with a substantially increased
groove depth, the composition of the data recording layer in lands
and grooves or the film thickness of a protective layer is made
substantially uniform. As a result, optical disks of excellent
reliability having uniform magnetic properties such as the optimal
data recording beam intensity in lands and grooves are manufactured
according to the current invention.
[0119] As described above, this invention substantially reduces
thermal crosstalk for optical disks and also can reduce both
thermal crosstalk and noise from the substrate. In addition, this
invention provides a method of recording on the above described
optical disks.
* * * * *