Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2002-07-03
2004-02-10
Neyzari, Ali (Department: 2655)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013320
Reexamination Certificate
active
06690624
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic lens which makes it possible to magnify and observe a minute magnetic domain contained in an object. The present invention also relates to a reproducing apparatus and a reproducing method for an information recording medium including a magnetic recording layer. In particular, the present invention relates to a magnetic reproducing element, a reproducing apparatus, and a reproducing method which make it possible to perform reproduction from an extremely minute magnetic domain while amplifying intensity of a reproduced signal.
2. Description of the Related Art
In recent years, the magneto-optical recording medium attracts the attention, which makes it possible to record a large amount of data at a high density and quickly perform recording and reproduction thereon, corresponding to the advance of multimedia. For example, the recording is performed on a magneto-optical recording medium capable of overwrite such that a laser beam is radiated onto the magneto-optical recording medium, and a magnetic field corresponding to input information is applied to a position irradiated with the laser beam. When the reproduction is performed on the magneto-optical recording medium as described above, a laser beam, which is weaker than that used upon the recording, is radiated onto the magneto-optical recording medium. Information is reproduced by detecting a polarization angle of a reflected laser beam depending on the direction of recording magnetization possessed by the returning light beam of the laser beam.
As shown in
FIG. 20
, a head mechanism, which is used for such a magneto-optical recording and reproducing apparatus, has been hitherto based on the use of an optical head
80
and a magnetic head
81
which are arranged on both sides of a disk recording medium respectively while opposing to one another with respect to the center line. In this arrangement, each of the optical head
80
and the magnetic head
81
has a large size and a large weight. Therefore, the respective heads
80
,
81
are supported by a support member
83
. A screw rotary shaft
84
is rotated by a driving motor
87
, and thus the respective heads
80
,
81
are moved over the disk recording medium
130
to record, reproduce, and erase the information. This system involves the following drawback. That is, the volume and the weight of the recording and reproducing apparatus are large, and it is impossible to respond, for example, to the demand for the small size, the light weight, the large capacity, and the high speed access upon recording, reproduction, and erasing which are required for the disk recording medium and for the recording and reproducing apparatus. On the other hand, a magneto-optical head mechanism
20
shown in
FIG. 21
is known as a technique to respond to the miniaturization of the recording and reproducing apparatus by integrating the optical head
80
and the magnetic head
81
into one unit. In this mechanism, a driving unit
73
for an objective lens
301
of an optical head system
72
, and a magnetic head slider
75
arranged with a magnetic head coil
76
are combined into one unit. A hole
77
is formed through the magnetic head slider
75
for transmitting a convergent light beam
74
of a laser beam
71
radiated from the optical head. The recording and reproducing apparatus based on the use of such a magneto-optical head has a considerably small volume. However, such an apparatus is insufficient to respond, for example, to the demand for the small size, the light weight, the large capacity, and the high speed access upon recording, reproduction, and erasing which are required for the recording and reproducing apparatus.
On the other hand, the magnetic hard disk is capable of rewriting recorded information. The magnetic hard disk is a recording medium having a large storage capacity and having high reliability. Therefore, the magnetic hard disk is practically used, for example, as a memory for the computer. However, the amount of information increases at a high speed, and the development of compact systems advances at a high-speed as well. It has been attempted to achieve recording at a higher density on the magnetic hard disk based on a method to perform reproduction by using the laser beam.
In order to increase the recording density of the magneto-optical recording medium, it is necessary to make the recording magnetic domain to be minute. The magnetic field modulation method is used for the recording on the magneto-optical recording medium, in which a magnetic field having a polarity corresponding to a recording magnetic domain signal is applied to a temperature-raised portion while irradiating the recording medium with a laser beam. This method is capable of overwrite recording, and it has succeeded in high density recording, for example, recording with a shortest mark length of 0.15 &mgr;m. Further, the light modulation recording system is also practically used, in which the recording is performed by radiating a power-modulated laser beam corresponding to a recording signal under a constant applied magnetic field. However, this method involves a problem concerning the resolution of an objective lens included in an optical head to be used when recorded minute recording magnetic domains are subjected to reproduction. The resolution has a limit value which is determined by the wavelength of the laser beam used upon reproduction and the numerical aperture N.A. of the objective lens. Reproduction is not achieved with minute magnetic domains of 0.15 &mgr;m as described above.
For example, as for minute recording magnetic domains or minute concave/convex pits to be subjected to high density recording, a minute mark having a magnetic domain length of 0.15 &mgr;m can be subjected to recording by using, for example, a laser beam having a spot diameter of 1 &mgr;m. However, in the present circumstances, it is impossible to perform reproduction while distinguishing minute magnetic domain signals of 0.15 &mgr;m by using the laser beam having the spot diameter of 1 &mgr;m as described above. An approach has been suggested in order to eliminate the limitation of the reproducing resolution due to the optical spot diameter of the reproducing light beam, i.e., for example, the magnetically induced super resolution technique (MSR) as described, for example, in
Journal of Magnetic Society of Japan
, Vol. 17, Supplemental S1, pp. 201 (1993). This technique utilizes the fact-that the temperature distribution appears on a magnetic film within a reproducing light spot when the magneto-optical recording medium is irradiated with a reproducing light beam, so that a magnetic mask is generated in the spot to reduce the effective spot diameter which contributes to the reproduction of the signal. The use of this technique makes it possible to improve the reproducing resolution without reducing the actual reproducing light spot diameter. However, in this technique, the amount of light, which contributes to the reproduction output, is lowered, and the reproduction C/N is lowered corresponding thereto, because the effective spot diameter is decreased by using the magnetic mask. As a result, it is difficult to obtain sufficient C/N, and hence it is difficult to practically use this technique.
Japanese Patent Application Laid-Open Nos. 1-143041, 6-295479, and 8-7350 disclose a method which uses a magneto-optical recording medium obtained by forming and stacking a magneto-optical recording layer and a recording magnetic domain-reproducing layer for transferring and magnifying recording magnetic domains to perform reproduction. However, in the case of the method described in each of the patent documents, the medium structure of the magneto-optical recording medium is complicated, and the production cost becomes expensive as well. Further, when the recorded magnetic signal is transferred to the reproducing layer, any noise such as leak magnetic field other than the reproducing magnetic signal is simultaneously transfer
Shimazaki Katsusuke
Tsuburaya Yoshitane
Hitachi Maxell Ltd.
Neyzari Ali
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