Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse...
Reexamination Certificate
1999-10-28
2001-11-06
Dinh, Tan (Department: 2651)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Reexamination Certificate
active
06314061
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Filed on the Invention
The present invention relates to a method for magneto-optical recordation and reproduction, and an apparatus therefor.
2. Related Background Art
Magneto-optical mediums are known, as a reloadable high density recording system, which record information by writing magnetic domains on a magnetic thin film with thermal energy of a semiconductor laser and reading out the information by utilizing magneto-optical effect. In recent years, the magneto-optical medium is required to record information in a still higher recording density for larger recording capacity.
The linear recording density of an optical disk such as magneto-optical mediums depends largely on the laser wavelength and the numerical aperture NA of the objective lens of the optical reproduction system. The beam waist diameter depends on the laser beam wavelength and the numerical aperture NA of the objective lens of the optical regeneration system, so that the detectable spatial frequency for record mark reproduction is limited approximately to 2NA/&lgr;. Therefore, for higher density of the conventional optical disks, the laser wavelength of the reproducing optical system should be shorter and the NA of the objective lens should be larger. However, improvements in the laser wavelength and in the numerical aperture of the objective lens are naturally limited. For further improvement of the recording density, techniques are being developed to improve a constitution of the recording medium and the method of readout.
For example, Japanese Patent Application Laid-Open No. 8-7350, discloses a magneto-optical recording medium and a magneto-optical recording-reproducing apparatus that use a domain-enlarging reproduction system. In this reproduction system, a magneto-optical disk has an exchange-coupled three-layered magnetic film as the memory layer; magnetic domains in the memory layer are transferred to the readout layer which is heated with a light spot to lower the coercivity force thereof; the transferred domains are enlarged by application of a reproducing magnetic field; and the information is reproduced by utilizing disappearance of the transferred and amplified domain by application of a reversed reproducing magnetic field. The process disclosed in the above laid-open publication is said to improve greatly the signal-to-noise ratio (S/N) of the reproduced signals of fine domains to enable a higher recording density.
The constitution of the magneto-optical recording reproduction apparatus of the domain-enlarging reproduction system is explained below, with reference to
FIG. 1
showing the constitution of the apparatus. In
FIG. 1
, magneto-optical disk
1
comprises a sample-servo substrate
2
, a magneto-optical medium
3
coating the substrate, and a protection layer
4
, where magneto-optical medium
3
is constituted of a memory layer and a readout layer. The apparatus has an objective lens
6
as the condenser lens, an actuator
5
for driving condenser lens
6
for focusing and tracking, a semiconductor laser
7
for projecting a light beam, a collimator lens
9
for collimating the light beam, a beam splitter
12
for separating the light beam, a &lgr;/2 plate
14
, a polarized beam splitter
15
, photosensors
17
for photoelectric conversion, and condenser lenses
16
for photosensors
17
.
Differential amplification circuit
18
amplifies differentially signals condensed and detected in the respective polarization directions of the light beam. Addition amplification circuit
19
adds and amplifies the signals condensed and detected in the respective polarization directions of the light beam. Magnetic head
26
applies, in recordation, a modulated magnetic field in accordance with signals to be recorded onto the laser-projected spot on magneto-optical disk
1
, and applies, in reproduction, an alternating magnetic field of a prescribed frequency. The magnetic head is placed in opposition to condenser lens
6
with the magneto-optical disk
1
interposed therebetween.
The magneto-optical recordation-reproduction method of the aforementioned domain-enlarging reproduction system is explained below with reference to the timing charts shown in
FIGS. 2A
to
2
H. Here, a method is explained for mark-edge recordation using a 1-7 code (RLL) as the memory modulation code.
FIG. 2A
shows a channel clock for 1-7 modulation codes in recordation.
FIG. 2B
shows a sequence of 1-7 NRZI recording signals outputted from controller
24
.
FIG. 2C
shows a sequence of record marks recorded by magnetic head
26
.
FIG. 2D
shows heated regions at the clock timing.
FIG. 2E
shows application of the reproducing magnetic field controlled by controller
24
.
FIG. 2F
shows reproduction signals corresponding to the record mark sequence shown in FIG.
2
C.
FIG. 2G
shows a reproduction clock signal.
FIG. 2H
shows reproduced binary signals corresponding to the record mark sequence shown in FIG.
2
C.
The recordation is conducted as follows. Field modulation recordation is conducted by projecting a recording DC laser power in a pattern shown in
FIG. 2B
by LD driver
25
and semiconductor laser
7
onto a magneto-optical disk
1
, corresponding to the channel clock shown in
FIG. 2A
, and applying a modulated magnetic field corresponding to the recordation signal by magnetic head driver
27
and driver
26
. Thereby, a sequence of record marks shown in
FIG. 2C
are formed on the memory layer by changing the direction of the recording magnetization in accordance with the information. In
FIG. 2C
, the shadowed portions and the unshadowed portions show magnetic domains magnetized in directions reverse to each other.
The reproduction is conducted as follows. In the reproduction, a reproduction clock signal is formed in synchronization with the record pattern. The reproduction clock signal is formed in synchronization with the recording pattern, for example, by a sample-servo system by detecting synchronization signals of the record pattern from clock pits preliminarily formed on magneto-optical medium
1
.
In the sample-servo system, the recordation is conducted also in synchronization with a clock signal formed by detection of the above clock pits. Therefore, by conducting the reproduction using the clock signal formed by detection of the clock pits, the recording and the reproduction can be synchronized with the clock signal.
Not only in the sample-servo system, a reproducing magnetic field can be applied in synchronization with the recorded domain sequence by conducting the recordation and reproduction by detecting the clock pits or the like formed preliminarily on the recording medium and conducting the recordation and the reproduction according to the clock signal.
In
FIGS. 2A
to
2
H, the channel clock shown in
FIG. 2A
corresponds to the clock signal formed during recordation, and the signal shown in
FIG. 2G
corresponds to the clock signal for reproduction. In
FIGS. 2A
to
2
H, the recordation phase and the reproduction phase are shifted by 180° from each other. The reproducing magnetic field is applied in synchronization with the reproduction clock shown in
FIG. 2G
at the timing shown in FIG.
2
E.
FIG. 2D
shows the sampling time for judgement of the level of the reproduction signal, namely the heated regions on the recording medium heated by light projection for reproduction at the clock timing. The reproduction light is not limited to DC light and pulse light, but may be any light which is capable of forming heated regions to cause transfer of recording magnetic domains onto the readout layer.
A reproducing magnetic field having the same frequency as the modulation code channel clock of
FIG. 2A
is applied to these heated regions. Thereby, a recorded domain, which is present in the heated region in the memory layer, is transferred to the readout layer and is enlarged instantaneously by application of the magnetic field in a domain-enlarging direction to cause a sharp change in the regeneration signal.
Conversely, by reversing the direction of the applied a
Canon Kabushiki Kaisha
Dinh Tan
Fitzpatrick ,Cella, Harper & Scinto
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