Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
1999-08-04
2003-09-23
Neyzari, Ali (Department: 2655)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013140
Reexamination Certificate
active
06625090
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magneto-optical recording medium in which the magnetically induced super-resolution technology is applied, and more particularly, to a magneto-optical recording/reproducing apparatus for such a magneto-optical recording medium.
To attain higher density of recording in a magneto-optical recording medium, magnetically induced super-resolution (MSR) technology has been proposed. With MSR technology the recording layer of a magneto-optical recording medium is formed from a minimum of three magnetic layers and magnetic switched coupling between the magnetic layers is utilized to assure a higher resolution than would be determined by the wavelength of a read light used.
MSR technology includes, for example, the FAD (front aperture detection) method in which the magnetic layer on the read light-irradiated side of a medium is magnetized in one direction in a high temperature area within a read light spot to detect signals from only a low temperature area, the RAD (rear aperture detection) method in which the magnetic layer on the read light-irradiated side is magnetized in one direction in a low temperature area within a read light spot to detect signals from only a high temperature area, the double-mask RAD method in which the magnetic layer on the read light-irradiated side is magnetized in one direction in the high and low temperature areas, respectively, within a read light spot to detect signals from only an intermediate temperature area between the high and low temperature areas, etc.
In all these methods, the area from which a signal is read by a read beam spot is narrow, which results in the same effect as would be obtained by reducing the size of the read beam spot. Therefore, it is possible to attain a higher density of recording in the magneto-optical recording medium than a resolution determined by the wavelength of a read light used.
To implement the above-mentioned MSR technology, when a read light is irradiated onto a magneto-optical recording medium to read information signals from the magneto-optical recording medium, it is necessary to apply a magnetic field to the magneto-optical recording medium in order to magnetize a part of the magneto-optical recording medium within a read light spot in one direction. The magnetic field will be referred to as “read-head field” hereinunder.
To enable use of MSR technology, the read-head field should desirably be reduced in strength. If a large read-head field has to be applied to enable the MSR technology, however, a magneto-optical recording/reproducing apparatus for use with the magneto-optical recording medium has to be provided with a special magnetic head which can apply such a large read-head field.
However, the magneto-optical recording apparatus basically comprises a writing magnetic head as a means for developing a magnetic field. When the read-head field may be small, the write head can be used to apply a read-head field.
SUMMARY OF THE INVENTION
Accordingly, the an object of the present invention is to overcome the above- mentioned drawbacks of the prior art by providing a magneto-optical recording medium in which MSR technology is applied and from which an information signal can be read with a small read-head field, and to provide a magneto-optical recording/reproducing apparatus adapted to read and write an information signal to/from such a magneto-optical recording medium.
The above object can be attained by providing a magneto-optical recording medium having:
a substrate having lands and grooves formed along a recording track; and
a recording layer formed on the substrate and consisting of a stack of at least three magnetic layers;
an information signal being written to the magneto-optical recording medium by the on-land recording method in which the information signal is written to the land; and
for reading the information signal from the magneto-optical recording medium, a magnetic field being applied to the magneto-optical recording medium so that a magnetic layer irradiated with a read light is magnetized in one direction in a part of the magnetic layer within a read light spot.
Because of the on-land recording method adopted, the MSR technology can be utilized to read an information signal from this magneto-optical recording medium with a smaller read-head field.
According to another aspect of the present invention, the magneto-optical recording medium should preferably be adapted such that when an information signal written on the magneto-optical recording medium is read, a read-head magnetic head is applied for the magnetic layer irradiated with a read light to be magnetized in predetermined directions in front and rear portions, respectively, lying in relation to the moving direction of the read light spot, of an area within the read light spot. In other words, the magneto-optical recording medium should preferably adopt the double-mask RAD method in the MSR technology. In the MSR technology, in particular, the double-mask RAD method attains a high resolution and thus permits to enable a higher density of recording in the magneto-optical recording medium.
According to another aspect of the present invention, the read-head field should preferably be 28,000 A/m or less in strength. The size of a magnetic field developed by a writing magnetic head provided in an ordinary magneto-optical recording/reproducing apparatus is on the order of 20,000 to 28,000 A/m. Therefore, by limiting the size of the read-head field to less than 28,000 A/m, it is possible to use the writing magnetic head as a magnetic head for application of a read-head field.
According to another aspect of the present invention, the magneto-optical recording medium should preferably be formed like a disc and have a plurality of recording bands defined by dividing a recording area thereof radially, the magneto-optical recording medium being spun at a predetermined speed with a write or read light focused within at least each of the recording bands when an information signal is written or read to/from the magneto-optical recording medium, the rotational speed or reference clock frequency being changed for each of the recording bands. In other words, the magneto-optical recording medium should preferably adopt the ZCAV (zone constant angular velocity) method. Adoption of the ZCAV method allows for an improved recording density without complicating the rotation drive circuitry of the magneto-optical recording/reproducing apparatus.
According to another aspect of the present invention, the magneto-optical recording medium should preferably be adapted such that when information signals written on the magneto-optical recording medium are read, a read-head magnetic head field is applied for the magnetic layer irradiated with a read light to be magnetized in predetermined directions in front and rear portions, respectively, lying in relation to the moving direction of the read light spot, of an area within the read light spot. In other words, the magneto-optical recording medium should preferably adopt the double-mask RAD method in the MSR technology. In the MSR technology, in particular, the double-mask RAD method attains a high resolution and thus permits to enable a higher density of recording in the magneto-optical recording medium.
According to another aspect of the present invention, to make the shortest recording pit length in the magneto-optical recording area smaller than that in the pit area, the shortest recording pit length in the pit area should preferably be an integral multiple of that in the magneto-optical recording area.
According to another aspect of the present invention, to make the shortest recording pit length in the magneto-optical recording area smaller than that in the pit area, the shortest recording pit length in the magneto-optical recording area should preferably be 0.38 &mgr;m or less and the shortest recording pit length in the pit area be 0.76 &mgr;m or less. Also, according to another aspect of the present invention, the track pitch should preferably be 0.9
Fukushima Yoshihito
Itoh Ken'ichi
Moribe Mineo
Numata Takehiko
Takemoto Hiroyuki
Neyzari Ali
Sonnenschein Nath & Rosenthal LLP
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