Optical disk and recording/reproducing device thereof

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

1997-06-04

2003-03-25

Hindi, Nabil (Department: 2653)

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

C369S275300, C369S047270

Reexamination Certificate

active

06538963

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disk and a recording/reproducing device thereof.
2. Discussion of the Related Art
Currently, when of information is recorded on an optical disk which has a 1.6&mgr; pitched spiral guide track of a recessed straight groove of about an ⅛ wavelength depth(called “groove track”), a data mark
9
corresponding to the information is recorded either on the recessed groove track or on a land track positioned between two recessed groove tracks. A laser beam, which is modulated according to a coded data, is focused on a micron spot of a size of less than 1&mgr; while optically detecting and tracking the center of the groove track using an actuator so as to record the information thereupon tracking the groove track by means of an actuator. DRAW(Direct Read After Write) recording media such as As—Te—Se, magnetic recording media such as Tb—Fe—Co, or phase change recording media such as Ge—Sb—Te are used as recording media. When reproducing the mark on the groove track thus recorded, a laser beam of a preset power is focused on a micron spot on the groove track having a size of less than 1&mgr; while optically identifying and tracking the groove track. Conventionally, the push-pull tracking has been used the optically track the groove track in a recording/reproduction.
The conventional push-pull tracking will be explained with reference to
FIGS. 5
a
,
5
b
,
6
a
and
6
b.
Referring to
FIGS. 6
a
and
6
b
, in a conventional pre-groove system, data is recorded/reproduced in sector units, with 20~40 sectors in a turn of a track pitched in general 1.6&mgr;. Each sector has a header region
2
and a data recording region
3
in a groove
4
of about ⅛ wavelength depth. The header region
2
has wobble pits
6
and
7
, and a sector mark
5
, shown in
FIG. 6
b
, consisting of a VFO(Variable Frequency Oscillator)
11
of continuous data pattern for locking a PLL(Phase Locked Loop), an AM(Address Mark)
12
, a sector address identifier(ID)
13
, an IEC(Identifier Error Corrector)
14
for detecting an error in the sector address identifier
13
, and a postamble(PA)
15
.
The wobble pits
6
and
7
on both sides of a center line
10
of the groove track
4
in the header region of
FIG. 6
a
are provided for solving problems following from aberrations of the optical spot
8
from the center line
10
during recording or reproduction caused by an error in a push-pull tracking signal detected from a reflected/diffracted signal at the pre-groove
4
coming from a slight adjustment deviation in the optical system. In other words, the error in the push-pull tracking signal is corrected to keep the optical spot always on the track center line
10
using the unbalance of optical spot
8
intensities back from the pair of wobble pits
6
and
7
caused when an error occurs in the push-pull signal and the optical spot comes out of the center line
10
of track
4
. This is a known art disclosed in JP Laid Open Patent No. S62-8341 for an composite type optical disk.
Currently, in order to record more data in an optical disk, land.groove recording is suggested in which, data is recorded on both of the land track and the recessed track to double a track density as shown in FIGS
5
a
and
5
b
. This land.groove recording is disclosed in papers such as N. Miyagawa, Y. Gotoh, K. Nishiuchi, E. Ohno and N. Akahira; “Land and Groove recording for high track density on phase change optical disks”, Jpn. J. Appl. Phys. 32, 5324/5328 (1993). In the push-pull tracking employed for optical tracking of the land, and groove tracks, a higher precision of tracking is required, and a slight adjustment deviation in the optical system causes a track offset which in turn causes a problem that the optical spot deviates from the center line of the land, or groove track during recording or reproduction. Consequently, even if the composite system disclosed in the JP Laid Open Patent No. S62-8341 is used, the land.groove disk still has difficulties correcting track offset errors which occur in the push-pull tracking such as incapability of disposal of the two wobble pits on both sides of the groove or land track that tend to occur when widths of the groove and land tracks become smaller to about 0.7&mgr;.
Moreover, as shown in
FIGS. 5
a
and
5
b
, each of the header regions
2
of the land track and the groove track should be provided with a synchronization mark and sector marks
5
such as a sector address. However, since a diameter of the optical spot is about 1&mgr;, an exact reproduction of sector information is not possible when attempting to read a sector mark
5
on, for example, a groove track because there is leakage of a sector mark signal at the side of the sector mark
5
to be read if the widths of the groove and land tracks become smaller than about 0.7&mgr;.
The tasks of the present invention for solve the aforementioned problems will be explained with reference to
FIGS. 5
a
and
5
b
taking the composite type optical disk using so called land groove disk, in which data is recorded on both of the groove track and the land track, as an example.
FIGS. 5
a
and
5
b
illustrate header regions of the composite type having the wobble pits known from the JP Laid Open Patent No. S62-8341 employed for use in suppressing an offset of a push-pull signal in the land.groove recording which doubles a track density by recording data on both of the land track
16
and recessed groove track
17
for providing a greater recording capacity in the optical disk. Referring to
FIGS. 5
a
and
5
b
, the push-pull tracking used to optically track the land track
16
or the groove track
17
requires higher precision tracking as a width of each of the land track
16
and the groove track
17
approaches about 0.7&mgr;, which is about one half of the track pitch p=1.6&mgr; of the conventional disk shown in
FIG. 6
a
. Consequently an optical spot
8
comes out of a track center line
18
or
19
of the land track or the groove track. To correct the deviation, the wobble marks
6
and
7
, should be added to each of the header regions
2
of the land track
16
and the groove track
17
. However, if a width of each of the land and groove tracks decreases to about 0.7&mgr;, it becomes difficult to reproduce wobble marks
6
and
7
having diameters of 0.35&mgr; which is half of the track width of p=0.7&mgr; as shown in
FIGS. 5
a
and
5
b
, using a focused optical spot having a diameter D calculated to be D=1.1 by an equation D=&lgr;/NA, where &lgr; is a wavelength and NA is a numerical aperture, when &lgr; is set to 0.65&mgr; and NA is set to 0.6. Consequently, problems in data recording/reproduction of the land.groove disk of narrow track widths are caused, such as incapability of correction of the offset occurring during the push-pull tracking, that significantly impedes putting the land.groove disk into practical use.
In addition, referring to
FIGS. 5
a
and
5
b
again, besides the wobble marks
6
and
7
, each of the header regions
2
of the land track
16
and the groove track
17
has, as shown in
FIG. 6
b
, a sector mark
5
consisting of a VFO
11
of continuous data pattern for locking a PLL, an AM
12
being an address mark, a sector address identifier(ID)
13
, an IEC
14
for detecting an error in the sector address identifier
13
, and a postamble(PA)
15
. If a width of each of the land and groove tracks becomes smaller to about 0.7&mgr;, the large optical spot of 1.1&mgr; diameter is likely to experience difficulties distinguishing VFO mark
11
in the header region
2
of the land track
16
from VFO mark
11
in the header region
2
of the adjacent groove track
17
due to cause cross-talk, which is a great cause of the error which occurs when reading in the signal of the header region
2
, a problem in making the tracks of the land.groove disk narrower, and a significant obstacle in putting the land.groove disk into practical use.
Still further, referring to
FIGS. 5
a

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