Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse...
Reexamination Certificate
1999-06-04
2001-06-19
Dinh, Tan (Department: 2753)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
C369S053130
Reexamination Certificate
active
06249490
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magneto-optical recording/reproducing method and apparatus capable of reproducing record marks by displacing domain walls of record marks in a reproducing layer by utilizing a temperature distribution gradient generated upon application of an optical beam to a magneto-optical recording medium having a multi-layer film structure, without changing record data in a record storage layer, and by detecting a change in a polarizing plane of a reflected optical beam.
2. Related Background Art
A magneto-optical recording medium of an erasable high density record type is known in which information is recorded by writing magnetic domains in a magnetic thin film with thermal energy supplied from a semiconductor laser and the information is read by utilizing the magneto-optical effect. Needs for increasing the record density of a magneto-optical recording medium to realize a high capacity have recently increased.
A linear record density of a magneto-optical recording medium or disk depends greatly on a laser wavelength and a numerical aperture NA of an objective lens of a reproducing optical system. Specifically, since a diameter of a beam waist is determined from a laser wavelength &lgr; and a numerical aperture NA of an objective lens of the reproducing optical system, a detection limit of a spatial frequency during reproduction of record magnetic domains is about 2 NA/&lgr;. In order to realize high density in a conventional magneto-optical disk, it is necessary to shorten the laser wavelength and increase the NA of an objective lens, respectively, of the reproducing optical system. There is a limit, however, in improving the laser wavelength and objective lens NA. For this reason, techniques of improving a record density have been developed by devising the structure of a recording medium and a read method.
For example, Japanese Patent Application Laid-open No. 06-290496 proposes a signal reproducing method and apparatus. With this method and apparatus, signals are recorded in a record storage layer of a multi-layer film constituted of a reproduction (domain wall displacement) layer and a magnetically coupled record storage layer. Domain walls of magnetic domains in the reproducing layer are displaced by utilizing a temperature gradient of a recording medium generated upon application of a heating optical beam, without changing record data in the record storage layer, the reproducing layer is magnetized so that almost all of the area of the reproducing optical beam spot has the same magnetization state, and a change in the polarized plane of a reflected reproducing optical beam is detected to reproduce recorded magnetic domains which are at the refraction limit or more of the optical system.
With this method, recorded magnetic domains having a period shorter than a diffraction limit of an optical system can be reproduced. Therefore, the record density and transfer speed of a magneto-optical recording medium can be considerably improved.
A recording/reproducing system using one beam in the signal reproducing method and apparatus disclosed in the above-cited publication will be described.
The structure of a photomagnetic recording/reproducing apparatus using a one beam recording/reproducing method will be described with reference to FIG.
1
. In
FIG. 1
, reference numeral
1
represents a magneto-optical disk which has a magnetic lamination film
3
and a protection film
4
formed on a substrate
2
made of glass or plastics. The magnetic lamination film
3
has a record storage layer and a domain wall displacement layer. Recorded magnetic domains can be reproduced by displacing domain walls of recorded magnetic domains in the domain wall displacement layer to broaden the magnetization area in a reproducing optical beam spot by utilizing a temperature distribution gradient generated upon application of an optical beam, without changing the record data in the record storage layer, and by detecting a change in a polarizing plane of a reflected optical beam. The magneto-optical disk
1
is supported by a spindle motor with a magnet chuck or the like, and is rotatable about the rotary shaft of the spindle motor.
Reference numerals
5
to
13
represent components constituting an optical head for applying a laser beam to the magneto-optical disk
1
and obtaining information from a reflected optical beam. Reference numeral
6
represents a condensing lens, reference numeral
5
represents an actuator for driving the condensing lens, reference numeral
7
represents a semiconductor laser as a light beam source, reference numeral
8
represents a collimator lens for converting an optical beam into a parallel light beam, reference numeral
9
represents a beam splitter for separating an optical beam, reference numeral
10
represents a &lgr;/2 plate, reference numeral
11
represents a polarizing beam splitter, reference numeral
13
represents a photosensor, reference numeral
12
represents a condensing lens for condensing an optical beam toward the photosensor, and reference numeral
14
represents a differential amplifier for differentially amplifying signals having different polarizing directions.
A laser beam emitted from the semiconductor laser
7
is applied to the substrate
2
of the magneto-optical disk
1
via the collimator lens
8
, beam splitter
9
and condensing lens
6
. In this case, the condensing lens
6
is displaced along the focussing direction and tracking direction under the control of the actuator
5
so that the laser beam is focussed upon the magnetic lamination film
3
, and also tracks a guide groove formed on the magneto-optical disk
1
. An optical path of a laser beam reflected at the magneto-optical disk
1
and passed through the condensing lens
6
is changed by the beam splitter
9
toward the polarizing beam splitter
11
. The laser beam is then picked up by the photosensors
13
as optical beams having different polarization angles depending upon the polarity of magnetization in the magnetic lamination film
3
, via the &lgr;/2 plate
10
, polarizing beam splitter
11
and condensing lens
12
. The outputs of the photosensors
13
are differentially amplified by the differential amplifier
14
which outputs a magneto-optical signal.
A controller
16
controls an LD driver
15
, a magnetic head driver
18
and the like by supplying a record power, a recording signal and the like in accordance with input information such as a revolution number of the magneto-optical disk
1
, a track position, a record radius, a record sector, a record start timing, a reproduction timing and the like. The LD driver
15
drives the semiconductor laser
7
while controlling the record power and reproduction power.
Reference numeral
17
represents a magnetic head for applying a modulating magnetic field to an area of the magneto-optical disk
1
where the laser beam is applied during the recording operation, and for applying a DC magnetic field during the reproducing operation. The magnetic head
17
is disposed facing the condensing lens
6
, with the magneto-optical disk
1
being interposed therebetween, and is displaced to a proper position during the recording/reproducing operation.
During the recording operation, the LD driver
15
drives the semiconductor laser
7
with a DC record power, and at the same time a magnetic head driver
18
drives the magnetic head
17
to generate a magnetic field having a polarity corresponding to the recording signal. For example, record magnetic domains are formed through a magnetic field modulation record method.
The magnetic head
17
and the magnetic head driver
18
for magnetic field modulation are used for applying a DC reproducing magnetic field during the reproducing operation.
As the laser beam is applied, the magnetic head
17
displaces in a radial direction of the magneto-optical disk
1
to sequentially apply a magnetic field to the magnetic lamination film
3
in the area where the laser beam is applied to thereby record and reproduc
Canon Kabushiki Kaisha
Dinh Tan
Fitzpatrick ,Cella, Harper & Scinto
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