Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse...
Reexamination Certificate
1998-01-13
2001-02-20
Neyzari, Ali (Department: 2651)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
C360S114050
Reexamination Certificate
active
06192008
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device and method for reproducing recorded information from a magneto-optical recording medium.
2. Discussion of Related Art
A magneto-optical recording medium employed in recording information has been practically utilized in situations where high-density rewritable media has been desired. The magneto-optical recording medium using a recording layer made of an amorphous alloy of a rare-earth element and a transition metal has been especially useful.
A method for recording information is described as follows. A laser beam is collimated onto a face of an optical recording medium to increase temperature of a small spot of the recording layer to about 150-200C. When the temperature exceeds a curie temperature (Tc) a magnetization phenomenon on the spot of the optical recording medium disappears. Then a biasing magnetic field is applied to orient the magnetic field of the spot, and the spot is allowed to cool to indoor temperature. The magnetic field of the spots is observable as recording marks (or pits).
A process for recording the information on a magneto-optical recording medium will be hereinafter illustrated referring to
FIGS. 1 and 2
.
FIG. 1
is a block diagram showing a general type of recording device and
FIG. 2
represents timing diagrams of the operation of the general recording device shown in FIG.
1
.
First, a channel clock generator
9
generates a channel clock signal
10
based on information pre-formatted on an optical disk. In response to the channel clock signal
10
, a laser driver
11
controls pulse beam emissions of a laser diode
1
. Such pulsed laser beam
2
is irradiated as an optics spot
4
onto an optical disk
8
through an object lens
3
.
Meanwhile, a data signal generator
6
forms a modulated magnetic field
7
by using a magnetic head
5
adjacent to the optical disk
8
.
As shown in
FIGS. 2A
to
2
E, the optical spot
4
is pulsed onto a face of the optical disk
8
synchronous with the frequency of the channel clock signal
10
. In such a process, the pulsing of laser beam
21
, the modulating of magnetic field
7
, and irradiating of the optic spot
4
occur synchronously to the channel clock signal
10
to record information onto the optical disk
8
. Marks are piled up on the optical disk
8
and recorded by such irradiated optic spots
4
. Magnetic pits having a shorter mark length than the optic spot
4
are recorded by such recording method, and such method is a well-known technique exhibited in Japanese Opening Patent No. Pyeong 1-292603.
In one method for reproducing the information written by the above recording method scheme on the optical disk, it is known in the art that the laser beam having a constant output is condensed and irradiated on the surface of the optical recording medium. The condensed optic spot is reflected on the surface of the magneto-optical recording medium, and a polarization state of the laser beam is changed by a Kerr effect. By detecting polarization state change of the reflected light, the information written on the disk can be read.
As shown in
FIG. 3A
, however, a problem occurs when density is increased. To increase density, the length of the magnetic mark becomes shorter. As a result, the optic spot becomes larger in relation to the length of the magnetic mark. Thus reproducing information becomes more error prone as the density increases.
A super resolution technique has been recently tried to overcome such shortcoming. A magnetically induced super resolution (MSR) using an exchange-combination force among multilayer films is provided as one settlement method out of the recent techniques.
One scheme for using an inner plane magnetization film in such MSR technique is offered in FIG.
4
. In this scheme, the magneto-optical recording medium is made up of two layer films of an exchange-combination structure formed by a reproducing layer having comparatively a little coercive force and a recording layer having comparatively a strong coercive force.
The reproducing layer serves as the inner plane magnetization film at indoor temperature, meantime over a constant temperature, its magnetization direction is changed and the reproducing layer represents a perpendicular magnetization.
The recording layer is formed by the perpendicular magnetization film to keep the information. When the optical beam is irradiated onto the reproducing layer to read the information, the innerplane magnetization is changed to the perpendicular magnetization, on the reproducing layer, by a pole Kerr effect, at a high temperature region of the optical spot, namely at the central region where the temperature is over a threshold value as shown in FIG.
4
. That is, the high temperature region of the reproducing layer is changed to the same direction as a magnetic field direction of the recording layer.
While, at low temperature regions peripheral to the high temperature region of the optical spot, the magnetization of the recording layer is masked since the pole Kerr phenomenon does not occur. Accordingly, a reproducing operation of the super resolution is available by properly selecting power of a reproducing laser beam, since recorded information is reproduced only at the high temperature region corresponding to the central portion of the optical spot.
One example of a device for reproducing the record information from the optical recording medium is shown in
FIG. 5
, and the timing diagrams are shown in
FIGS. 6A-6E
. This reproducing device employs a pulsed laser beam as the reproducing light. A reproducing clock generator
58
outputs a reproducing clock signal shown in
FIG. 6A and a
pulse generator
57
outputs a pulse type signal based on the reproducing clock signal. A laser driver
56
drives laser diode
55
in response to the pulsed signal. The pulsed laser beam emitted as shown in
FIG. 6B
from the laser diode
55
is condensed onto an optical recording medium
51
through a condenser
54
and an object lens
52
. An optical spot condensed on the optical recording medium
51
is reflected and enters a first polarized beam splitter
53
through the object lens
52
. The optical spot from the first polarized beam splitter
53
enters a second polarized beam splitter
59
, and at this time, a P polarization element is let through and an S polarization element is reflected.
The P polarization element and the S polarization element are respectively condensed by a first photo detector
61
and a second photo detector
60
, and converted into electrical signals. The converted signals are inputted to a differential amplifier
62
to be differentially amplified, and applied to a reproducing signal processor
63
. The reproducing signal processor
63
processes the signal from the differential amplifier
62
and outputs a bit signal, namely a binary signal as detected information.
FIG. 6D
represents writing marks written on the optical recording medium
51
shown in FIG.
5
. In
FIG. 6D
, hatched marks indicate a binary signal of a high level and white marks indicates a binary signal of a low level.
A magnetic amplifying magneto-optical system (MAMMOS) has been used as a technique to overcome problems related to high density writing as depicted in FIG.
3
. Such technique realizes higher writing density by employing a magnetic film of two layers formed by a recording layer and an enlarged reproducing layer.
In this technique, an alternating reproducing magnetic field is applied onto the recording medium, to thereby enlarge a minute magnetic domain of a high density disk, copy the domain on the enlarged reproducing layer, and thus increase a detected reproducing signal. As shown in
FIG. 6C
, the alternating magnetic field is made up of a magnetic field signal of an up magnetization direction corresponding to a binary signal of a high level and a magnetic field signal of a down magnetization direction corresponding to a binary signal of a low level.
The alternating reproducing magnetic field is applied onto the recording medium reg
LG Electronics Inc.
Neyzari Ali
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