Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2000-09-29
2004-10-05
Dinh, Tan (Department: 2651)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013050
Reexamination Certificate
active
06801478
ABSTRACT:
BACKGROUND OF THE INVENTION
i) Field of the Invention
The present invention relates to a magneto-optical information reproducing apparatus for reproducing information recorded in a recording medium in which a groove and a land are alternately formed and the information is recorded both in the groove and land by applying a magnetic field to the recording medium and irradiating the recording medium with light.
ii) Description of Related Art
An optical recording medium has heretofore been used broadly as a recording medium by which a sound signal and an image signal can be recorded/reproduced. Particularly, a magneto-optical recording medium has been noted as a high-density recording medium which can rewrite information, and intensively researched/developed. Moreover, a magneto-optical information reproducing apparatus for reproducing the information recorded in the magneto-optical recording medium has also been intensively researched/developed.
The magneto-optical recording medium generally has a disk form, and is provided with a spiral or concentric track, and the information is recorded in the track. Moreover, in order to enhance a recording density of the magneto-optical recording medium, two techniques of shortening a track pitch and of enhancing a linear recording density are considered. Either technique can be realized by shortening a wavelength of a semiconductor laser for use in recording/reproducing, but it takes some more time to realize a semiconductor laser in an inexpensive manner which continuously oscillates a short wavelength of green or blue at a room temperature steadily for a long time.
In this situation, a technique is sought which uses a semiconductor laser with the current wavelength to largely improve the linear recording density, such as a magnetic super resolution (hereinafter referred to as MSR) for applying a reproducing magnetic field to the magneto-optical recording medium to limit a reproducing object to an area smaller than a laser spot.
Moreover, as the technique of shortening the track pitch, a technique of land and groove recording has been proposed in which the information is recorded both in a furrow-like groove and a ridge-like land alternately disposed on the recording medium. In this land and groove recording, both the groove and the land are used as the track. Therefore, in the land and groove recording, as compared with a technique of using only one of the groove and the land as the track, the track pitch simply becomes ½. When the linear recording density is the same, the recording density can be doubled. Therefore, this technique is considerably important in realizing a high-density recording.
Additionally, in the land recording in which the information is recorded only in the land, the groove exists between adjacent lands, there is a gap between the lands in which the information is recorded, and occurrence of a crosstalk in which the information recorded in the adjacent land is mixed into reproducing information is therefore inhibited.
FIG. 1
is a diagram showing that the information recorded by the land recording is read.
Here, a groove
2
narrower than a land
1
is formed between the lands
1
, and a recording mark
3
in accordance with the information is formed only on the land
1
. Specifically, only the land
1
is used as the track, and a track pitch is, for example, about 0.9 &mgr;m. Moreover, the information is recorded by a mark space row constituted of the recording marks
3
and spaces
3
′ between the marks.
Moreover,
FIG. 1
shows that the recording marks
3
are read by the aforementioned MSR. In the recording medium for the MSR system, the recording mark
3
and space
3
′ are in magnetization states different in magnetization direction from each other, the magnetization state of the recording mark
3
is hereinafter referred to as a recording state, and the magnetization state of the space
3
′ is hereinafter referred to as a clear state. Moreover, the information is read by recognizing these magnetization states, but for the sake of convenience of description, the recognition of the magnetization state is sometimes referred to as “reading of the recording mark”.
During the reading of the recording mark
3
, a laser spot
4
is tracked on the land (track)
1
, and relatively moved in a direction of an arrow F with respect to the land
1
so that the recording mark
3
is read. In this case, a reproducing magnetic field is applied to an area held between a dotted line L
1
and a dotted line L
2
. When the reproducing magnetic field and heat by the laser spot
4
both act on a material constituting the magneto-optical recording medium, a front mask
4
a
and rear mask
4
b
are formed to hide the presence of the recording mark
3
. As a result, a range
4
c
in which the recording mark
3
can be read is limited to a range smaller than an irradiation range of the laser spot
4
, and even the recording marks
3
recorded within a laser spot diameter can be read one by one. Moreover, by recognizing the recording mark
3
and space
3
′ constituting the mark space row, the information is reproduced.
As described above, since the groove
2
is formed between the lands
1
, the recording mark
3
on a land
1
b
adjacent to a land
1
a
in which the laser spot
4
is tracked fails to enter the range
4
c
in which the recording mark can be read, and occurrence of the crosstalk is inhibited.
Similarly, in groove recording in which the information is recorded only in the groove, the land exists between adjacent grooves, there is a gap between the grooves in which the information is recorded, and occurrence of the crosstalk in which the information recorded in the adjacent groove is mixed into the reproducing information is inhibited. On the other hand, in the land and groove recording in which the information is recorded both in the land and the groove, no gap exists between the tracks, the occurrence of the crosstalk from the groove adjacent to the land or from the land adjacent to the groove cannot be avoided, and a large influence is therefore exerted to information reproducing ability.
FIG. 2
is a diagram showing that the information recorded by the land and groove recording is read.
Here, the land
1
and groove
2
with the same width are alternately formed, and the mark space row constituted of the recording marks
3
and spaces
3
′ in accordance with the information is formed both on the land
1
and groove
2
. Specifically, both the land
1
and the groove
2
are used as the tracks, and the track pitch is a narrow pitch, for example, of about 0.6 &mgr;m.
FIG. 2
also shows that the recording mark
3
is read by the aforementioned MSR, and here shows, as one example, that the recording mark
3
on the land
1
is read. By irradiating the land
1
as a reading object track with the laser spot
4
, relatively moving the laser spot
4
in the direction of the arrow F, and applying the reproducing magnetic field to the area held between the dotted lines L
1
and L
2
, the front mask
4
a
and rear mask
4
b
are formed.
As described above, since the recording mark
3
is written both in the land
1
and groove
2
, the recording mark readable range
4
c
also reaches the recording mark
3
on the groove
2
adjacent to the land
1
in which the laser spot
4
is tracked, and the crosstalk occurs.
For example, in Japanese Patent Application Laid-Open No. 7357/1996, a technique of appropriately selecting a groove depth and reducing the crosstalk from the land or the groove is proposed. However, in the groove with the selected depth, a carrier level corresponding to original reproducing information is lowered, and there is also a problem that a push/pull signal level for use as a tracking error signal is similarly lowered. Moreover, it has been already reported that the crosstalk reduction effect obtained by selecting the groove depth is easily collapsed by fluctuation of Kerr ellipticity, and focus error, spherical surface aberration, and the like of an objective lens.
Moreover,
Dinh Tan
Fujitsu Limited
Greer Burns & Crain Ltd.
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