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| United States Patent | 5407720 |
| Link to this page | http://www.wikipatents.com/5407720.html |
| Inventor(s) | Omata; Hiroshi (Kawasaki, JP) |
| Abstract | An optical recording medium has tracking tracks and recording tracks
interposed between the tracking tracks. The width of the recording tracks
in a specific region is larger than that in other region. |
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Title Information  |
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Drawing from US Patent 5407720 |
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Optical recording medium and process for producing the same |
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| Publication Date |
April 18, 1995 |
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| Filing Date |
November 16, 1993 |
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| Parent Case |
This application is a continuation of application Ser. No. 07/769,808 filed
Oct. 2, 1991, now abandoned. |
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| Priority Data |
Oct 03, 1990[JP]2-263840 |
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Title Information |
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References |
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| Market Size |
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Estimate the gross annual revenues of the relevant market
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| Reasonable Royalty |
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Public's "Guesstimation" of Royalty Value
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Market Review |
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Technical Review |
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Claims |
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What is claimed is:
1. An optical recording medium which comprises: tracking tracks and
recording tracks interposed between the tracking tracks, the width l.sub.3
of the tracking tracks in a specific region and the width l.sub.1 of the
tracking tracks in another region have the following relationship:
0.60.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95,
the specific region being a prepit region provided with prepits on the
recording track.
2. An optical recording medium according to claim 1, wherein the specific
region is a closest prepit region.
3. An optical recording medium according to claim 1, wherein the width of
the recording tracks in the specific region is smaller than the diameter
of a light beam spot which a light beam for either recording or
reproducing, or both recording and reproducing forms on a substrate
surface.
4. An optical recording medium according to claim 1, wherein width l.sub.4
of the recording tracks in the specific region and width l.sub.2 of the
recording tracks in the another region have the following relationship:
0.7.ltoreq.l.sub.2 /l.sub.4 .ltoreq.1.0.
5. An optical recording medium according to claim 4, wherein the
relationship is:
0.7.ltoreq.l.sub.2 /l.sub.4 .ltoreq.0.8.
6. An optical recording medium according to claim 1, wherein the
relationship is:
0.7.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95.
7. An optical recording medium according to claim 1, wherein the optical
recording medium is used in a recording apparatus for detecting tracking
errors by a push-pull method.
8. An optical recording medium according to claim 1, wherein the optical
recording medium is used in a reproduction apparatus for detecting
tracking errors by a push-pull method.
9. An optical recording medium according to claim 1, wherein the tracking
tracks are grooves formed on a substrate.
10. An optical recording medium according to claim 9, wherein the depth of
the grooves is set to be smaller than .lambda./4n, but larger than
.lambda./8n, where .lambda. is the wavelength of an irradiating light beam
irradiating the substrate and n is the refractive index of the substrate.
11. An optical recording medium according to claim 10, wherein the depth of
the grooves is not more than .lambda./5n, but not less than .lambda./7n.
12. An optical recording medium according to claim 11, wherein the depth of
the grooves is not more than .lambda./5n, but not less than .lambda./6n.
13. An optical recording medium according to claim 1, wherein the specific
region is region between the prepits.
14. An optical recording medium according to claim 1, wherein said optical
recording medium is an optomagnetic medium.
15. An optical recording medium according to claim 1, wherein a width
l.sub.4 of the recording tracks in the specific region is larger than a
width l.sub.2 of the recording tracks in the another region.
16. An optical recording medium which comprises: tracking grooves and
recording tracks interposed between the tracking grooves, the depth
d.sub.2 of a groove in a specific region and the depth d.sub.1 of a groove
in another region having the following relationship:
0.80.ltoreq.d.sub.2 /d.sub.1 .ltoreq.0.95,
the specific region being a prepit region provided with prepits on the
recording track.
17. An optical recording medium according to claim 16, wherein the specific
region is a closest prepit region.
18. An optical recording medium according to claim 16, wherein the optical
recording medium is used in a recording apparatus for detecting tracking
errors by a push-pull method.
19. An optical recording medium according to claim 16, wherein the optical
recording medium is used in a reproduction apparatus for detecting
tracking errors by a push-pull method.
20. An optical recording medium according to claim 16, wherein the grooves
are formed on a substrate.
21. An optical recording medium according to claim 20, wherein the depth
d.sub.1 of the grooves in the another region satisfies the following
relationship:
.lambda./8n.ltoreq.d.sub.1 .ltoreq..lambda./4n
wherein .lambda. is the wavelength of an irradiating light beam irradiating
the substrate and n is the refractive index of the substrate.
22. An optical recording medium according to claim 21, wherein the depth
d.sub.1 satisfies the following relationship:
.lambda./7n.ltoreq.d.sub.1 .ltoreq..lambda./5n.
23. An optical recording medium according to claim 22, wherein the depth
d.sub.1 satisfies the following relationship:
.lambda./6n.ltoreq.d.sub.1 .ltoreq..lambda./5n.
24. An optical recording medium according to claim 16, wherein depth
d.sub.2 of the grooves in the specific region satisfies the following
relationship:
.lambda./8n.ltoreq.d.sub.2 .ltoreq.d.sub.1.
25. An optical recording medium according to claim 24, wherein the depth
d.sub.2 satisfies the following relationship:
.lambda./8n.ltoreq.d.sub.2 .ltoreq..lambda./6n.
26. An optical recording medium according to claim 16, wherein the optical
recording medium is a disk-type, optical recording medium.
27. An optical recording medium according to claim 16, wherein the specific
region is region between the prepits.
28. An optical recording medium according to claim 16, wherein said optical
recording medium is an optomagnetic medium.
29. An optical recording medium which comprises: tracking grooves and
recording tracks interposed between the tracking grooves, the width
l.sub.3 of a tracking groove in a specific region and the width l.sub.1 of
a tracking groove in another region having the following relationship:
0.60.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95,
and the depth d.sub.2 of the groove in the specific region and the depth
d.sub.1 of a groove in the another region having the following
relationship:
0.80.ltoreq.d.sub.2 /d.sub.1 .ltoreq.0.95,
the specific region being a prepit region provided with prepits on the
recording track.
30. An optical recording medium according to claim 29, wherein said optical
recording medium is an optomagnetic medium.
31. An optical recording medium according to claim 29, wherein the specific
region is a closest prepit region.
32. An optical recording medium according to claim 29, wherein the width of
the recording tracks in the specific region is smaller than the diameter
of a light beam spot which a light beam for either recording or
reproducing, or both recording and reproducing forms on a substrate
surface of the recording medium.
33. An optical recording medium according to claim 29, wherein the width
l.sub.4 of the recording tracks in the specific region and the width
l.sub.2 of the recording tracks in the another region having the following
relationship:
0.7.ltoreq.l.sub.3 /l.sub.4 .ltoreq.1.0.
34. An optical recording medium according to claim 33, wherein the
relationship of widths l.sub.2 and l.sub.4 is:
0.7.ltoreq.l.sub.2 /l.sub.4 .ltoreq.0.8.
35. An optical recording medium according to claim 33, wherein the
relationship of widths l.sub.3 and l.sub.1 is:
0.7.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95.
36. An optical recording medium according to claim 29, wherein said optical
recording medium comprises means for being used in a recording apparatus
for detecting tracking errors by a push-pull method.
37. An optical recording medium according to claim 29, wherein said optical
recording medium comprises means for being used in a reproducing apparatus
for detecting tracking errors by a push-pull method.
38. An optical recording medium according to claim 29, wherein the specific
region is a region between prepits.
39. An optical recording medium according to claim 29, wherein the tracking
grooves are formed on a substrate.
40. An optical recording medium according to claim 29, wherein the depth
d.sub.1 of the grooves in the another region satisfies the following
relationship:
.lambda./8n.ltoreq.d.sub.1 .ltoreq..lambda./4n
wherein .lambda. is the wavelength of an irradiating light beam irradiating
the optical recording medium and n is the refractive index of the
substrate.
41. An optical recording medium according to claim 40, wherein the depth
d.sub.1 satisfies the following relationship:
.lambda./7n.ltoreq.d.sub.1 .ltoreq..lambda./5n.
42. An optical recording medium according to claim 41, wherein the depth
d.sub.1 satisfies the following relationship:
.lambda./6n.ltoreq.d.sub.1 .ltoreq..lambda./5n.
43. An optical recording medium according to claim 29, wherein the depth
d.sub.2 of the groove in the specific region satisfies the following
relationship:
.lambda./8n.ltoreq.d.sub.2 .ltoreq.d.sub.1.
44. An optical recording medium according to claim 29, wherein the depth
d.sub.2 of the groove in the specific region satisfies the following
relationship:
.lambda./8n.ltoreq.d.sub.2 .ltoreq..lambda./6n.
45. An optical recording medium according to claim 29, wherein the optical
recording medium is a disk-type optical recording medium.
46. An optical recording medium according to claim 29, wherein a width
l.sub.4 of the recording tracks in the specific region is larger than
width l.sub.2 of the recording tracks in the another region.
47. A substrate for an optical recording medium which comprises: tracking
tracks and recording tracks interposed between the tracking tracks, the
width l.sub.3 of the tracking tracks in a specific region and the width
l.sub.1 of the tracking tracks in another region having the following
relationship:
0.60.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95 /--13 --
the specific region being a prepit region provided with prepits on the
recording track.
48. A substrate for an optical recording medium, which comprises: tracking
grooves and recording tracks interposed between the tracking grooves, the
depth d.sub.2 of a groove in a specific region and the depth d.sub.1 of
the groove in the another region having the following relationship:
0.80.ltoreq.d.sub.2 /d.sub.1 .ltoreq.0.95,
the specific region being a prepit region provided with prepits on the
recording track.
49. A substrate for an optical recording medium, which comprises: tracking
grooves and recording tracks interposed between the tracking grooves, the
width l.sub.3 of a tracking groove in a specific region and the width
l.sub.1 of a tracking groove in another region having the following
relationship:
0.60.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95,
and the depth d.sub.2 of a groove in the specific region and the depth
d.sub.1 of the groove in the another region having the following
relationship:
0.80.ltoreq.d.sub.2 /d.sub.1 .ltoreq.0.95,
the specific region being a prepit region provided with prepits on the
recording track.
50. An optical recording medium which comprises: tracking grooves and a
recording track interposed between the tracking grooves, the depth d.sub.2
of a groove in a specific region being smaller than the depth d.sub.1 of a
groove in another region, the depth d.sub.1 satisfying the following
relationship:
.lambda./7n/.ltoreq.d.sub.1 .ltoreq..lambda./5n,
and the depth d.sub.2 satisfying the following relationship:
.lambda./8n/.ltoreq.d.sub.2 .ltoreq..lambda./6n,
the specific region being a prepit region provided with prepits on the
recording track, and wherein X is the wavelength of a reproducing beam to
reproduce information from the optical recording medium and n is the
refractive index of a substrate on which the grooves and recording track
are formed.
51. An optical recording medium which comprises: tracking grooves and a
recording track interposed between the tracking grooves, the width l.sub.3
of a tracking groove in a specific region and the width l.sub.1 of a
tracking groove in another region having the following relationship:
0.60.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95,
the depth d.sub.2 of a groove in the specific region being smaller than the
depth d.sub.1 of a groove in the another region, the depth d.sub.1
satisfying the following relationship:
.lambda./7n.ltoreq.d.sub.1 .ltoreq..lambda./5n,
and the depth d.sub.2 satisfying in the following relationship:
.lambda./8n.ltoreq.d.sub.2 .ltoreq..lambda./6n,
the specific region being a prepit region provided with prepits on the
recording track, wherein .lambda. is the wavelength of a reproducing beam
reproducing information from the optical recording medium and n is the
refractive index of a substrate on which the grooves are formed.
52. A substrate for an optical recording medium, which comprises: tracking
grooves and a recording track interposed between the tracking grooves, the
depth d.sub.2 of a groove in a specific region being smaller than the
depth d.sub.1 of a groove in another region, the depth d.sub.1 satisfying
the following relationship:
.lambda./7n.ltoreq.d.sub.1 .ltoreq..lambda./5n
the depth d.sub.2 satisfying the following relationship:
.lambda./8n.ltoreq.d.sub.2 .ltoreq..lambda./6n
the specific region being a prepit region provided with prepits on the
recording track, wherein .lambda. is the wavelength of a reproducing beam
reproducing information on the substrate and wherein n is the refractive
index of the substrate.
53. A substrate for an optical recording medium, which comprises: tracking
grooves and a recording track interposed between the tracking grooves, the
width l.sub.3 of a tracking groove in a specific region and the width
l.sub.1 of a tracking groove in another region having the following
relationship:
0.60.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95,
the specific region being a prepit region provided with prepits on the
recording track.
54. An optical recording medium comprising: a substrate and a recording
layer, the substrate comprising tracking tracks and a recording track
interposed between the tracking tracks, the width l.sub.3 of a tracking
track in a specific region and the width l.sub.1 of a tracking track in
another region having the following relationship:
0.60.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95,
the specific region being a prepit region provided with prepits on the
recording track.
55. An optical recording medium comprising: a substrate and a recording
layer, the substrate comprising tracking grooves and a recording track
interposed between the tracking grooves, the depth d.sub.2 of a groove in
a specific region and the depth d.sub.1 of a groove in another region
having the following relationship:
0.80.ltoreq.d.sub.2 /d.sub.1 .ltoreq.0.95,
the specific region being a prepit region provided with prepits on the
recording track.
56. An optical recording medium which comprises: tracking tracks and
recording tracks interposed between the tracking tracks, wherein the
relationship between the width l.sub.3 of the tracking tracks in a prepit
region provided with prepits on the recording track and the width l.sub.1
of the tracking tracks in another region is set so that offset quantities
of a tracking error signal in the prepit region and another region are
substantially equal.
57. An optical recording medium which comprises: tracking grooves and
recording tracks interposed between the tracking grooves, wherein the
relation between the depth d.sub.2 of a groove in a prepit region provided
with prepits on the recording track and the depth d.sub.1 of a groove in
another region is set so that offset quantities of a tracking error signal
in the prepit region and another region are substantially equal.
58. An optical recording medium which comprises: a tracking track and a
recording track adjacent thereto, the width l.sub.3 of the tracking track
in a specific region and the width l.sub.1 of the tracking track in
another region have the following relationship:
0.60.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95
the specific region being a prepit region provided with prepits on the
recording track.
59. An optical recording medium which comprises: a tracking groove and a
recording track adjacent thereto, the depth d.sub.2 of a groove in a
specific region and the depth d.sub.1 of a groove in another region having
the following relationship:
0.80.ltoreq.d.sub.2 /d.sub.1 .ltoreq.0.95,
the specific region being a prepit region provided with prepits on the
recording track.
60. An optical recording medium which comprises: a tracking groove and a
recording track adjacent thereto, the width l.sub.3 of a tracking groove
in a specific region and the width l.sub.1 of a tracking groove in another
region having the following relationship:
0.60.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95,
and the depth d.sub.2 of the groove in the specific region and the depth
d.sub.1 of a groove in the another region having the following
relationship:
0.80.ltoreq.d.sub.2 /d.sub.1 .ltoreq.0.95,
the specific region being a prepit region provided with prepits on the
recording track.
61. A substrate for an optical recording medium which comprises: a tracking
track and a recording track adjacent thereto, the width l.sub.3 of in a
specific region and the width l.sub.1 of the tracking tracks in another
region having the following relationship:
0.60.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95,
the specific region being a prepit region provided with prepits on the
recording track.
62. A substrate for an optical recording medium, which comprises: a
tracking groove and a recording track adjacent thereto, the depth d.sub.2
of a groove in a specific region and the depth d.sub.1 of the groove in
the another region having the following relationship:
0.80.ltoreq.d.sub.2 /d.sub.1 .ltoreq.0.95,
the specific region being a prepit region provided with prepits on the
recording track.
63. A substrate for an optical recording medium, which comprises: a
tracking groove and a recording track adjacent thereto, the width l.sub.3
of a tracking groove in a specific region and the width l.sub.1 of a
tracking groove in another region having the following relationship:
0.60.ltoreq.l.sub.3 /l.sub.5 .ltoreq.0.95,
and the depth d.sub.2 of a groove in the specific region and the depth
d.sub.1 of the groove in the another region having the following
relationship:
0.80.ltoreq.d.sub.2 /d.sub.1 .ltoreq.0.95,
the specific region being a prepit region provided with prepits on the
recording track.
64. An optical recording medium which comprises: a tracking groove and a
recording track adjacent thereto, the depth d.sub.2 of a groove in a
specific region being smaller than the depth d.sub.1 of a groove in
another region, the depth d.sub.1 satisfying the following relationship:
.lambda./7n.ltoreq.d.sub.1 .ltoreq..lambda./5n,
and the depth d.sub.2 satisfying the following relationship:
.lambda./8n.ltoreq.d2.ltoreq..lambda./6n,
the specific region being a prepit region provided with prepits on the
recording track, and wherein .lambda. is the wavelength of a reproducing
beam to reproduce information from the optical recording medium and n is
the refractive index of a substrate on which the grooves and recording
track are formed.
65. An optical recording medium which comprises: a tracking groove and a
recording track adjacent thereto, the width l.sub.3 of a tracking groove
in a specific region and the width l.sub.1 of a tracking groove in another
region having the following relationship:
0.60.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95,
the depth d.sub.2 of a groove in the specific region being smaller than the
depth d.sub.1 of a groove in the another region, the depth d.sub.1
satisfying the following relationship:
.lambda./7n.ltoreq.d.sub.1 .ltoreq..lambda./5n,
and the depth d.sub.2 satisfying in the following relationship:
.lambda./8n.ltoreq.d.sub.2 .ltoreq..lambda./6n,
the specific region being a prepit region provided with prepits on the
recording track, wherein .lambda. is the wavelength of a reproducing beam
reproducing information from the optical recording medium and n is the
refractive index of a substrate on which the groves are formed.
66. A substrate for an optical recording medium, which comprises: a
tracking groove and a recording track adjacent thereto, the depth d.sub.2
of a groove in a specific region being smaller than the depth d.sub.1 of a
groove in another region, the depth d.sub.1 satisfying the following
relationship:
.lambda./7n.ltoreq.d.sub.1 .ltoreq./5n,
the depth d.sub.2 satisfying the following relationship:
.lambda./8n.ltoreq.d.sub.2 .ltoreq..lambda./6n,
the specific region being a prepit region provided with prepits on the
recording track, wherein .lambda. is the wavelength of a reproducing beam
reproducing information on the substrate and wherein n is the refractive
index of the substrate.
67. A substrate for an optical recording medium, which comprises: a
tracking groove and a recording track adjacent thereto, the width l.sub.3
of a tracking groove in a specific region and the width l.sub.1 of a
tracking groove in another region having the following relationship:
0.60.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95,
the specific region being a prepit region provided with prepits on the
recording track.
68. An optical recording medium comprising: a substrate and a recording
layer, the substrate comprising a tracking track and a recording track
adjacent thereto, the width l.sub.3 of a tracking track in a specific
region and the width l.sub.1 of a tracking track in another region having
the following relationship:
0.60.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95,
the specific region being a prepit region provided with prepits on the
recording track.
69. An optical recording medium comprising: a substrate and a recording
layer, the substrate comprising a tracking groove and a recording track
adjacent thereto, the depth d.sub.2 of a groove in a specific region and
the depth d.sub.1 of a groove in another region having the following
relationship:
0.80.ltoreq.d.sub.2 /d.sub.1 .ltoreq.0.95,
the specific region being a prepit region provided with prepits on the
recording track.
70. An optical recording medium which comprises: a tracking track and a
recording track adjacent thereto, wherein the relationship between the
width l.sub.3 of the tracking tracks in a prepit region provided with
prepits on the recording track and the width l.sub.1 of the tracking
tracks in another region is set so that offset quantities of a tracking
error signal in the prepit region and another region are substantially
equal.
71. An optical recording medium which comprises: a tracking groove and a
recording track adjacent thereto, wherein the relation between the depth
d.sub.2 of a groove in a prepit region provided with prepits on the
recording track and the depth d.sub.1 of a groove in another region is set
so that offset quantities of a tracking error signal in the prepit region
and another region are substantially equal. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical recording medium having tracks capable
of recording optically reproducible data, and more particularly to an
optical recording medium having tracking tracks for following tracks
capable of recording data, that is, for tracking, and also to a process
for producing the optical recording medium.
2. Related Background Art
Generally, an optical recording medium, such as an optical disk, an
optomagnetic disk, etc. has data recording tracks (which will be
hereinafter referred to as "recording tracks") and tracking tracks formed
in a manner optically discriminatable from the recording tracks so that a
recording-reproducing beam may correctly follow the recording tracks. On
the recording tracks which are each interposed between the tracking
tracks, address data for providing positional information on the recording
tracks to an optical head control system, etc. are formed in advance as
prepits.
The prepits are recesses each having a depth of an odd number multiple of
.lambda./4n (wherein .lambda. is the wavelength of reproducing beam and n
is the refractive index of the substrate) so selected as to usually
provide a maximum modulation to the reproducing beam, that is, a tracking
beam, irradiating the optical recording medium so that the reproducing
beam may pass through the substrate. As tracking tracks, grooves formed on
the substrate are usually used.
So far known methods for detecting tracking errors of such an optical disk
include the so called push-pull method and the three-beam method. The
push-pull method comprises using a single beam and outputting the
difference in the outputs of reflected and diffracted beam lights of an
incident single beam on and from the disk at two light-receiving sections
of two divided parts of a photodiode, the two divided parts being
symmetrically provided at the track center, thereby detecting a tracking
error. The three-beam method comprises using a main beam for recording and
reproducing data onto and from recording tracks and further using primary
light diffracted by a diffraction grating as auxiliary beams at the same
time, and outputting the difference in the outputs of the reflected light
of the auxiliary beams at two light-receiving sections receiving the
reflected light, thereby detecting a tracking error.
When the prepit length and the prepit distance are shortened in such an
optical recording medium to increase the recording density, as shown, for
example, in FIGS. 15 and 16, the amplitude W.sub.16 of quantity of
reflected light (difference in the brightness) is decreased and the S/N of
the prepits is also lowered, if the spot size of reading beam is constant.
This tendency is particularly remarkable for prepits formed on the
recording tracks on the inner peripheral portion of a disk-type optical
recording medium, because, when a reading light spot is placed between one
prepit and another, no sufficient quantity of reflected light can be
obtained due to the interference from the preceding and successive
prepits. If the pit size of the prepits is reduced to decrease the
interference from the prepits, insufficient darkness can be obtained when
the reading light spot is on the prepit, and thus there is no more
improvement in the signal output. That is, even if the pit shape is
changed, there are still such problems that in case the reading light spot
size is constant, no sufficient signal output can be obtained at parts of
the disk having a shorter pit distance when the recording density of
address data is increased.
SUMMARY OF THE INVENTION
The present invention has been accomplished to solve the foregoing problems
encountered so far in the relevant art.
An object of the present invention is to provide an optical recording
medium capable of increasing the signal output of prepits, particularly at
parts of the disk having shorter prepit distance, and a process for
producing the same.
Another object of the present invention is to provide an optical recording
medium capable of increasing the signal output of prepits and preventing a
decrease in the amplitude of a tracking error signal in the prepit region
at the same time, and a process for producing the same.
Another object of the present invention is to provide an optical recording
medium capable of increasing the signal output of the prepit region,
outputting even tracking error signals throughout the entire surface of
the optical recording medium and preventing any leak-in of pulse signals
generated at AT signals in the prepit region due to DC offsets, thereby
obtaining AT signals with less noise.
That is, the present invention provides an optical recording medium which
comprises tracking tracks and recording tracks interposed between the
tracking tracks, the width of the recording tracks in a specific region
being larger than that in another region.
The present invention also provides an optical recording medium which
comprises tracking grooves and recording tracks interposed between the
tracking grooves, the depth of tracking grooves in a specific region being
smaller than that in another region.
The present invention further provides an optical recording medium which
comprises tracking grooves and recording tracks interposed between the
tracking grooves, the width of the recording tracks in a specific region
being larger than that in another region and the depth of the tracking
grooves in the specific region being smaller than that in the another
region.
The present invention further provides a substrate for an optical recording
medium, which comprises tracking grooves and recording tracks interposed
between the tracking grooves on the surface, the width of the recording
tracks in a specific region being larger than that in another region.
The present invention further provides a substrate for an optical recording
medium, which comprises tracking grooves and recording tracks interposed
between the tracking grooves, the depth of the tracking grooves in a
specific region being smaller than that in another region.
The present invention further provides a substrate for an optical recording
medium, which comprises tracking grooves and recording tracks interposed
between the tracking grooves on the surface, the width of the recording
tracks in a specific region being larger than that in another region and
the depth of the tracking grooves in the specific region being smaller
than that in the another region.
The present invention further provides a process for producing a stamper
for molding a substrate for an optical recording medium comprising
tracking grooves and recording tracks interposed between the tracking
grooves on the surface, the depth of the tracking grooves in a specific
region being smaller than in another region, which comprises:
a) a step of forming a photoresist layer on a substrate for a master,
b) a step of exposing the photo-resist layer to a converged laser beam by
scanning in accordance with the pattern of the tracking grooves,
c) a step of developing the photo-resist layer after the light exposure,
thereby forming the master, and
d) a step of forming an electroconductive layer on the photoresist
layer-formed surface of the master, then electrodepositing a metallic
layer onto the electroconductive layer, thereby integrating the
electroconductive layer with the metallic layer and then separating the
metallic layer from the master, where the power of the converged laser
beam for the pattern light exposure in accordance to the tracking grooves
in the specific region is modulated to a lower level than that of the
converged laser beam for the pattern light exposure in accordance with the
tracking grooves in the other region in the step (b) of the light
exposure.
The present invention further provides a process for producing a stamper
for molding a substrate for an optical recording medium comprising
tracking grooves and recording tracks interposed between the tracking
grooves, the width of the recording tracks in a specific region being
larger than that in another region, which comprises:
a) a step of forming a photoresist layer on a substrate for a master,
b) a step of exposing the photoresist layer to a converged laser beam by
scanning in accordance with the pattern of the trackings grooves,
c) a step of developing the photoresist layer after the light exposure,
thereby forming the master, and
d) a step of forming an electrophotoconductive layer on the photoresist
layer-formed surface of the master, then electro-depositing a metallic
layer onto the electroconductive layer, thereby integrating the
electroconductive layer with the metallic layer and then separating the
metallic layer from the master, where the spot size of the converged laser
beam for the pattern light exposure in accordance with the tracking
grooves in the specific region is made smaller than the spot size of the
converged laser beam for the pattern light exposure in accordance with the
tracking grooves in the other region.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an enlarged plan view of a prepit region of one embodiment of an
optical recording medium according to the present invention.
FIG. 2 is a schematic diagram showing a signal output in the prepit region
of the optical medium shown in FIG. 1.
FIG. 3 is an enlarged plan view of a prepit region of another embodiment of
an optical recording medium according to the present invention.
FIG. 4 is a cross-sectional view in the direction vertical to the track in
the data region of the optical recording medium shown in FIG. 3.
FIG. 5 is a cross-sectional view of the closest provided prepit region of
the optical recording medium shown in FIG. 3.
FIG. 6 is a schematic diagram showing signal outputs in the prepit region
of the optical recording medium shown in FIG. 3.
FIG. 7 is a schematic diagram showing relations between the tracking error
signal, the modulation degree of groove-traversing signal, and the groove
depth.
FIGS. 8A and 8B are schematic diagrams for explaining the modulation degree
of a groove-traversing signal; and
FIGS. 9A-1, 9A-2 and 9A-3 are cross-sectional views of the data region and
the prepit region of the conventional optical recording medium and the
prepit region of the present optical recording medium, respectively, and
FIG. 9B is a schematic diagram showing relations of tracking error signals
in each of those regions.
FIG. 10 is a schematic diagram showing the relation between the groove
depth and the quantity of reflected light.
FIGS. 11A and 11B are schematic views of a further embodiment of an optical
recording medium according to the present invention.
FIGS. 12A and 12B are a schematic view and a schematic diagram of a still
further embodiment of an optical recording medium according to the present
invention, respectively.
FIG. 13 is a schematic cross-sectional view of the injection molding of an
optical recording medium according to the present invention.
FIG. 14 is an enlarged plan view of an optical recording medium produced in
the manner shown in FIG. 13.
FIG. 15 is an enlarged plan view of the prepit region of the conventional
optical recording medium.
FIG. 16 is a schematic diagram showing signal outputs in the prepit region
of the optical recording medium shown in FIG. 15.
FIG. 17 is a graph showing reproduced signal outputs of an optomagnetic
disk according to Example 9.
FIG. 18 is a graph showing reproduced signal outputs of an optomagnetic
disk according to Reference Example 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be explained in detail below, referring to the
accompanying drawings.
FIG. 1 is an enlarged plan view of a prepit region in one embodiment of an
optical recording medium according to the present invention, and FIG. 2 is
a diagram showing signal outputs (reflected light quantity) in the prepit
region.
In FIG. 1, I is a data region, II a prepit region and III a closest pit
region in the prepit region, and numeral 1 is a groove as a tracking
track, 1' a groove formed in the prepit region II, and 3 is a prepit
formed in a recording track 2. Width l.sub.3 of groove 1' is so set that
width l.sub.4 of recording track 2' in the prepit region II may be larger
than width l.sub.2 of recording track 2 in the data region I, where
l.sub.4 <l.sub.5 (light spot size), whereby the area occupied by the
groove in a light spot 4 for irradiating the recording track can be
reduced and consequently a decrease in the quantity of reflected light can
be prevented even if an interference occurs between the diffracted,
reflected light and the zero-ordered diffracted light in the groove. As a
result, the desired quantity of reflected light can be maintained between
the prepits in the prepit region, particularly in the closest pit region
III, as shown in FIG. 2, and thus sufficient signal outputs can be
obtained.
By maintaining relations between the width l.sub.2 of recording track 2 and
the width l.sub.4 of recording track 2' in a ratio l.sub.2 /l.sub.4 of 0.7
to 1.0, particularly 0.7 to 0.8 in such a range that l.sub.4 may not
exceed l.sub.5 in the present invention, a decrease in the signal outputs
of prepits, and the reflected light quantity particularly between the pits
in the closest pit region can be preferably suppressed. In the present
invention, the light spot size has such a diameter that the intensity of
light beam is 1/e.sup.2 of the intensity at the center.
In the present invention, the depth of groove 1 is set to be smaller than
.lambda./4n, but larger than .lambda./8n. That is, when grooves are used
as tracking tracks, it is known that the tracking error signal will be a
maximum when the depth of grooves is set to .lambda./8n (where n:
refractive index of a substrate; .lambda.: wavelength of recording and/or
reproducing light beam), as shown in FIG. 10, but the modulation degree of
the groove-traversing signal for discriminating the recording tracks from
the grooves is lowered during the track seeking, when the depth of groove
is made smaller than .lambda./4n, which provides a maximum modulation
degree of diffraction, as shown in FIG. 7, and thus it is desirable to set
the depth of the groove a little larger than .lambda./8n, specifically to
.lambda./5n to .lambda./7n, particularly preferably .lambda./5n to
.lambda./6n.
In the foregoing embodiment, it is preferable to set the relations between
the width l.sub.1 of groove 1 and the width l.sub.3 of groove 1' to that
represented by the following relationship (1), particularly (2):
0.60.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95 (1)
0.7.ltoreq.l.sub.3 /l.sub.1 .ltoreq.0.95 (2)
That is, in the case of decentering an objective lens to conduct
microseeking, etc. in the tracking according to the push-pull method, a
light spot will be displaced even on 2D-PD, and a DC offset that fails to
make an AT signal zero is generated even if the light spot is at the track
center. To solve the problem, adjustment is made, for example, by
subtracting the offset quantity from the AT signal. The proportion of the
offset quantity to the AT signal is proportional to the amplitude of AT
signal, when the decentering degree of an objective lens and the groove
shape are constant. When the push-pull method is used in the tracking of
the conventional optical recording medium, on the other hand, the
reflected light diffracted at the prepit in the prepit region interferes
with the reflected light in another region of the recording track,
resulting in a reduction of quantity of reflected light and thus there is
a tendency for a decrease to occur in the amplitude of the tracking error
signal (AT signal). Thus, there are still such problems that the offset
quantity is less in the prepit region than in the data region, resulting
in a difference in the offset quantity between these two regions, whereas
the offset adjustment in the data region gives rise to an offset in the
prepit region (these phenomena will be referred to as "leak-in").
When the width l.sub.3 of groove 1' in the prepit region is made so small
as to satisfy the foregoing relation, the ratio of the offset quantity to
the amplitude of AT signal can be increased in the prepit region II, as
compared with that in the data region I, and thus the difference in the
offset quantity can be made substantially zero between the data region and
the prepit region even if the amplitude of AT signal is decreased in the
prepit region as in the foregoing, whereby the offset can be surely
adjusted. This is because the diffraction efficiency of the light beam due
to the grooves can be lowered by decreasing the groove width and the ratio
of zero-ordered diffracting light on 2D-PD to first-ordered diffraction
light can be increased, resulting in an increase in the ratio of the
offset quantity to the amplitude of AT signal.
FIG. 3 is a plan view showing a second embodiment of an optical recording
medium according to the present invention and FIGS. 4 and 5 are schematic
cross-sectional views along the lines A--A' and B-B' of FIG. 3,
respectively, where numeral 1 is a groove in the data region I, 1' a
groove in the prepit region II, and 3 is a prepit formed on a recording
track 2.
In the second embodiment, groove 1' is so formed that the depth d.sub.2 may
be smaller than that d.sub.1 of groove 1 in the data region, as shown in
FIGS. 4 and 5. That is, in the second embodiment, the interference can be
decreased between the diffracted, reflected light by groove 1' and the
zero-ordered diffracted light in the prepit region II, and thus the
reduction in the quantity of reflected light can be suppressed and the
decrease in the amplitude of the quantity of reflected light can be
suppressed between the prepits in the prepit region, for example, the
closest pit region III, as shown in FIG. 6, whereby a sufficient signal
output of prepits can be maintained.
In the case of an optical recording disk having a preformat with the width
of groove 1: 0.5 mm and track pitch: 1.6 .mu.m, where recording and
reproduction are carried out with a light beam having a wavelength
.lambda. and a spot size of 1.5 .mu.m, it is known that a maximum tracking
error signal can be obtained in the second embodiment when the depth
d.sub.1 of group 1 is .lambda./8n (n: refractive index of the substrate).
When the depth of the groove is made smaller from .lambda./4n which gives
the maximum modulation degree, the modulation degree of the
groove-traversing signal for use in the discrimination of recording tracks
from the groove at the track seeking is lowered, as shown in FIG. 7, and
thus it is preferable to set the depth of the groove to be a little larger
than .lambda./8n, and more specifically .lambda./5n to .lambda./7n,
preferably .lambda./5n to .lambda./6n.
It is preferable to set the depth d.sub.2 of groove 1' in the prepit region
II to be smaller than at least d.sub.1, and when d.sub.2 is set to about
.lambda./8n, and a sufficient quantity of reflected light can be obtained
between the prepits in the prepit region, particularly the closest prepit
region III, without any substantial occurrence of tracking errors. The
modulation degree of a groove-traversing signal can be represented by
(I.sub.top -I.sub.bottom)/I.sub.0 , where I.sub.top is the quantity of
reflected light at the recording track, I.sub.bottom the quantity of
reflected light at the groove and I.sub.0 is the quantity of reflected
light at the mirror surface and changes in the quantity of reflected light
observed when a light spot is scanned in the groove-traversing direction,
are shown in FIGS. 8A and 8B.
In the foregoing embodiment, it is particularly preferable to set d.sub.2
to .lambda./6n to .lambda./8n. That is, when the depth of groove in the
data region and that in the prepit region are both set to be larger than
.lambda./8n in the push-pull method, as shown in FIGS. 9A-1, 9A-2 and
9A-3, the reflected light diffracted at the prepit interferes with the
reflected light at other part in the recording track region, resulting in
a decrease in the quantity of reflected light, whereas since the depth of
the groove in the groove region is also set to be larger than .lambda./8n,
the quantity of reflected light is lower. That is, there is a tendency for
the amplitude of the tracking error signal (AT signal) to be decreased.
For example, when a light head is moved to a specific recording track,
generally the number of recording tracks traversed is determined by
counting AT signals. Lower AT signals only in the prepit region at that
time is liable to cause errors such as miscounting, etc. However, by
setting d.sub.2 to the foregoing range as shown in FIG. 9AIII, the
quantity of reflected light at the groove is increased to prevent lowering
of the amplitude of AT signals in the prepit region, thereby prov | | |
