Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2002-01-31
2003-06-24
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013540
Reexamination Certificate
active
06584044
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for recording information on the recording layer of a magneto-optical recording medium. In particular, the invention relates to a recording method and a recorder which make it possible to form, on the recording layer of a magneto-optical recording medium, record marks from which information can be reproduced stably regardless of mark lengths of the record marks.
2. Description of Related Art
Optical recording media such as magneto-optical recording media are known as external memories for computers etc. Magneto-optical recording media can take or cover a great quantity of data such as dynamic images and voice, and are therefore used frequently as recording media in this multimedia era. In general, bits of information “1” and “0” are recorded as the presence and absence of record marks on a magneto-optical recording medium. For example, the light intensity modulation method and the magnetic field modulation method are known as methods of recording information on magneto-optical recording media.
The light intensity modulation method involves recording information by radiating a laser beam which intensity is modulated with record information, while applying a DC magnetic field to the recording layer of a magneto-optical recording medium. While the magnetic field in one direction is always applied, the information is recorded. Therefore, in order to record new information on that part of the recording layer where old information has been recorded, it is necessary to erase the old information before recording the new one. The magnetic field modulation method involves recording information by applying a magnetic field pulsed in accordance with bits of data, while radiating a DC laser beam onto the recording layer of a magneto-optical recording medium. It is possible to record the data by reversing the direction of magnetization of (part of) the recording layer with the recording magnetic field according to each bit of information “1” or “0”. It is therefore possible to directly overwrite data. Because the DC laser beam is radiated, however, the record marks become crescent in shape and longer tangentially of the recording medium as the linear velocity increases. This is disadvantageous in processing the reproduced signals.
The optical (or light) magnetic field modulation method is known as an improvement on the magnetic field modulation method. The optical magnetic field modulation (light pulse-magnetic field modulation) method involves applying a magnetic field polarized in accordance with a record signal while radiating a light beam pulsed in synchronism with a recording clock. This method overcomes or eliminates the disadvantage of the magnetic field modulation method, and makes it possible to form minute recorded magnetic domains for high-density recording.
For densely recorded information, however, a number of recorded magnetic domains will be present within a reproducing light beam spot, and it is therefore not possible to reproduce information individually from them. In other words, the resolution of the reproducing light beam is insufficient to reproduce the information individually from the minute recorded magnetic domains. It is therefore necessary to reproduce information from minute recorded magnetic domains with a reproducing light beam spot having the conventional diameter.
As a method of solving this problem, the magnetically induced super resolution technique (MSR) is suggested in, for example, Journal of Magnetic Society of Japan, Vol. 17, Supplement, No. S1, pp. 201 (1993). Even if two recorded magnetic domains are present within a reproducing light beam spot, this technique makes it possible to reproduce information from one of the domains by masking the other out of sight to narrow the effective field of view. The use of this technique makes it possible to improve the reproducing resolution without reducing the diameter of the actual reproducing light beam spot. Even with the magnetically induced super resolution technique, however, the strength of the signal reproduced from each of the magnetic domains does not change, and therefore the C/N ratio of the reproduced signal is still low.
The inventor has disclosed in International Publication No. WO98/02878 a magneto-optical recording medium including a domain enlarging and reproducing layer and a recording layer which lie on a substrate. During reproduction, the minute magnetic domains on the recording layer are transferred individually to the reproducing layer while a reproducing magnetic field is applied to the reproducing layer so that the domains transferred to the reproducing layer can be enlarged and reproduced. The magnetic domains transferred to the domain enlarging and reproducing layer are enlarged approximately up to the light beam spot size. This remarkably increases the strength of the reproduced signals. This technique is called the MAMMOS (magnetic amplifying magneto-optical system), which solves the problem with the magnetically induced super resolution technique about the C/N ratio of the signals reproduced from minute magnetic domains.
The MSR and MAMMOS involve utilizing the magnetic leakage fields leaking from the recorded magnetic domains in the recording layer of a magneto-optical recording medium to transfer the information on this layer to the reproducing layer of the medium, and thereafter reading out the information from the reproducing layer. However, it has been found that, under such a method or system, if the recording layer of a magneto-optical recording medium includes a continuous recorded magnetic domain (record mark)
227
consisting of two or more bits of information as shown in
FIG. 2
, the signal reproduced from the domain
227
is unstable in comparison with that from a shortest recorded magnetic domain which is present independently in the recording layer. This is conceived to be due to the difference in magnitude between the magnetic leakage fields at end portions and a middle portion of a continuous record mark formed on the recording layer. In particular, the magnetic leakage field leaking from the middle portion is weaker than that leaking from each of the end portions. It is consequently difficult to transfer the information on a middle portion of a continuous record mark to the reproducing layer. Therefore, in order to reproduce the information from a shortest record mark and the information from a continuous record mark, it is necessary to strictly control the power of the reproducing magnetic field and the power of the reproducing light beam, causing the problem that the reproducing power margins become narrower.
Japanese Patent Application Laid-Open No. 2-101659 discloses a method of recording binary information by pairing minimum record units and making the units of any pair different in magnetization. However, this Japanese publication does not show recording with a continuous recorded magnetic domain divided into magnetic domains magnetized in alternate directions.
SUMMARY OF THE INVENTION
In view of the problems with the foregoing prior art, it is an object of the present invention to provide a recording method making it possible to form, on the recording layer (of a magneto-optical recording medium), record marks which can be transferred reliably or securely to the reproducing layer (of the medium) during reproduction of information regardless of mark lengths of the marks.
It is another object of the invention to provide a recorder which can record continuous record marks having stable reproducing characteristics on the recording layer of a magneto-optical recording medium.
In accordance with a first aspect of the invention, a recording method is provided for recording information on a magneto-optical recording medium by radiating a recording light beam onto the medium while applying a magnetic field in a recording direction to the medium, the method comprising:
assigning one bit of information to a combination of a magnetic domain magnetized in th
Awano Hiroyuki
Sekine Masaki
Tani Manabu
Yoshihiro Masafumi
Dinh Tan
Hitachi Maxell Ltd.
Oliff & Berridg,e PLC
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