Optical disk and recording/reproducing device

Details Optical disk and recording/reproducing device Optical disk and recording/reproducing device

2001-01-26

2003-10-07

Kelly, Cynthia H. (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

Recording medium or carrier

C428S064100, C369S275400

Reexamination Certificate

active

06630219

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to magneto-optical and other optical disks where a stable tracking control is effected by means of restraint of crosstalk which may occur in the information pre-recorded in the form of pit strings and changes in the track width, and also relates to recording/reproducing devices intended for use with these disks.
BACKGROUND OF THE INVENTION
Magneto-optical disks as rewritable optical recording media are already have been already developed from magneto-optical recording media and put into practical use. Stored data is deleted on these kinds of magneto-optical disks by a semiconductor laser emitting a light beam which is focused on the optical recording media to locally elevate the temperature of the magneto-optical recording media. To reproduce recorded data, a light beam is focused on the magneto-optical recording media with such an intensity that the data is not deleted, and the polarization of the reflected light is checked. To reproduce address information on these magneto-optical recording media, continuous pit strings are typically provided in advance in a recording track to form a spiral line or concentric lines on the disk substrate, and the quantity of reflected light is measured for changes which result from the provision of the pit strings.
Meanwhile, super-resolution magnetic reproduction has been developed based on a multilayered magnetic film. In addition, the reproduction resolution of super-resolution magneto-optical recording media has improved a lot. These are contributing factors in the great effort put in those researches about land and groove recording schemes whereby data is recorded and reproduced both in the groove region serving as a guide groove and in the land region serving as another guide groove. In the land and groove recording scheme, the land and the groove constitute individual recording tracks, and require separate sets of address bits.
Now reference is made to
FIG. 20
which illustrates a structure of address bits disclosed in Japanese Laid-Open Patent Application No. 7-153081/1995 (Tokukaihei 7-153081 published on Jun. 16, 1995; hereinafter, “Laid-Open Patent Application 1”). Grooves (G
1
, G
2
) and lands (L
1
, L
2
) are provided to form spiral lines with a substantially identical width. A first pit string P
1
representing first address information is provided following the groove G
1
, to form convexities and concavities in a first address region. A second pit string P
2
is provided following the groove G
2
in a second address region that is displaced along the length of the track off the first address region where the first pit string P
1
is provided.
Now, the following will discuss how to reproduce the address information. In a case when a light beam spot BG
1
scans the groove G
1
relatively as a result of the rotation of the optical disk, the address information of the groove G
1
is reproduced by detecting the quantity of reflected light which varies when the light beam spot BG
1
scans the first pit string P
1
in the first address region. The light beam spot BG
1
then passes over the second address region. In a case when a light beam spot BG
2
scans the groove G
2
relatively, the address information of the groove G
2
is reproduced by detecting the quantity of reflected light which varies when the light beam spot BG
2
first passes over the first address region and then scans the second pit string P
2
in the second address region.
In contrast, in a case when a light beam spot BL
1
scans the land L
1
relatively, the address information of the land L
1
is reproduced by detecting signals which leak from the first pit string P
1
and which changes the quantity of reflected light when the light beam spot BL
1
scans near the first pit string P
1
in the first address region. In a case when a light beam spot BL
2
scans the land L
2
relatively, the address information of the land L
2
reproduced by detecting signals which leak from the second pit string P
2
and which changes the quantity of reflected light when the light beam spot BL
2
scans near the second pit string P
2
in the second address region. This way, an optical disk is made such that address information can be reproduced both in the land and in the groove.
Now reference is made to
FIG. 21
which illustrates a structure of addresses disclosed in Japanese Laid-Open Patent Application No. 9-17033/1997 (Tokukaihei 9-17033 published on Jan. 17, 1997; hereinafter, “Laid-Open Patent Application 2”). Grooves (G
1
, G
2
) and lands (L
1
, L
2
) are provided to form spiral lines with a substantially identical width. A first pit string P
1
representing first address information is provided following the groove G
1
in a first address region. A second pit string P
2
is provided following the groove G
2
in a second address region that is displaced off the first address region along the length of the track. The width of the groove is widened partially in radial directions to form pits p
1
and p
2
in the first and second pit strings P
1
and P
2
.
The address information is reproduced, similarly to Laid-Open Patent Application 1, through changes in the quantity of reflected light in the address regions in the land and in the groove. This way, an optical disk is made such that address information can be reproduced both in the land and in the groove.
Now reference is made to
FIG. 22
which illustrates a structure of addresses disclosed in Laid-open Patent Application 2. Grooves (G
1
, G
2
) and lands (L
1
, L
2
) are provided to form spiral lines with a substantially identical width. A wobbling groove representing address information is provided following the groove G
1
in a first address region. Another wobbling groove representing address information is provided following the groove G
2
in a second address region displaced off the first address region along the length of the track.
The address information is reproduced and detected, similarly to Laid-Open Patent Application 1, by means of the wobbling grooves causing changes in the quantity of reflected light in the address regions in the land and in the groove. This way, an optical disk is made such that address information can be reproduced both in the land and in the groove. Alternatively, the address information is reproduced and detected by means of the wobbling grooves in the address regions caused changes in push-pull signals.
Laid-Open Patent Application 1, however, admits in the description that tracking is unstable. We now discuss this problem in the following.
FIG. 23
is an enlarged view of the first address region of FIG.
20
. Symmetric push-pull signals are obtained from the light beam spot BG
1
scanning the groove G
1
, and tracking is effected such that the first pit string P
1
is always located in the center of the light beam spot BG
1
, because the first pit string P
1
cuts through the center of the light beam spot BG
1
.
In contrast, since the pit string P
1
is located to the left of the light beam spot BL
1
(or closer to the circumference of the disk, for example) in the first address region in the figure, asymmetric push-pull signals are obtained from the light beam spot BL
1
scanning the land L
1
where there is a gap between pits p
1
which are located next to each other along the length of the track. As a result, the light beam spot BL
1
moves left as shown in the figure (closer to the pit string P
1
) while tracking, which renders the tracking unstable. In a worst scenario, the light beam spot BL
1
jumps to a different track when moving in the address region. Therefore, in some devices for recording/reproducing such optical disks, a tracking control is temporarily suspended in the address region.
Laid-Open Patent Application 2 also admits in the description that tracking is unstable.
FIG. 24
is an enlarged view of the first address region in FIG.
21
. The formation of the first pit string P
1
constituted by pits p
1
that are wider than the groove in the first address region makes push-pull signals obtained from the light beam

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