Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
1999-03-30
2002-05-14
Neyzari, Ali (Department: 2651)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
Reexamination Certificate
active
06388954
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magneto-optical recording medium having an information recording layer and a reproducing layer, together with a method of recording and reproducing the same, and an apparatus for recording and reproducing it. More specifically, it relates to a magneto-optical recording medium capable of generating a clock which is precisely synchronised with a recording domain recorded on the information recording layer, together with a method of recording and reproducing the same, and an apparatus for recording and reproducing it.
2. Description of the Related Art
Magneto-optical recording media and other magneto-optical discs are familiar as external memory in computers and elsewhere. Magneto-optical recording media permit the rewriting of information, and their capacity to handle large volumes of moving image, sound and other data has led to their frequent use as recording media in this multimedia ages. In recent years there have been calls for further increases in the storage capacity of such magneto-optical recording media, and one method of achieving this would be to make the recording magnetic domains even smaller and record information at higher densities. Recording with smaller recording magnetic domains is possible if a light pulse magnetic field modulation process is adopted whereby a magnetic field of a polarity depending on the recording signal is applied while irradiating with light which has been modulated into pulse form in synchrony with the recording clock.
However, any attempt to generate magnetic microdomains encounters the problem that it is impossible to make the spot diameter of the reproducing light smaller than the NA limit of the light head, and there is no way of reproducing separately a plurality of magnetic microdomains existing within the reproducing light spot. One suggested method of solving this problem is by means of the technique of magnetic super-resolution (MSR) (
Journal of the Magnetic society of Japan
, vol. 17, suppl. S1, p. 201, 1993). According to this technique, it is possible to reproduce one of two recording magnetic domains existing within a reproducing light spot by masking the other so that it cannot be seen, thus narrowing the effective field of vision. However, the strength of the reproduction signal from each of the magnetic domains remains the same, with the result that the C/N is low.
In International Patent Application WO98/02878 the inventors of the present invention have disclosed a magneto-optical recording medium which has a magnetic domain magnification reproducing layer and a recording layer on the substrates making it possible to transfer the magnetic microdomains of the recording layer separately at reproduction, and by applying a reproducing electric field to enlarge the magnetic domains which have been transferred to the recording layer prior to reproducing them. This magneto-optical recording medium facilitates a marked increase in the strength of the reproduction signal because the magnetic domains which are transferred on to the magnetic domain magnification reproducing layer are enlarged (magnified) to roughly light spot size. The technique has been given the name of MAMMOS (Magnetic Amplifying Magneto-Optical System), and serves to solve the problems inherent in the above-mentioned magnetic super-resolution technique in relation to the reproduction S/N of magnetic microdomains.
In MAMMOS, not only do the magnetic domains recorded on the recording layer need to be enlarged at the moment when they are transferred to the reproducing layer, but the enlarged magnetic domains must be erased immediately before the next recording magnetic domain is scanned by the light spot. For this reason, it is necessary to control the timing with which the external magnetic field is applied and the polarity reversed. MAMMOS is in the process of becoming a very important technique for improving recording density, but on the other hand certain problems become evident as the density increases.
The process whereby information is recorded on to a magneto-optical recording medium involves either light modulation, electric field modulation or a combination of the two. Whatever process is adopted, it is normal to detect a pre-pit formed on the substrate, thus generating a clock, which then becomes the criterion for irradiating with light and/or applying an external magnetic field, in accordance with the information which is to be recorded.
In the above-mentioned method of recording, however, the recording layer is irradiated with recording light and heated to a prescribed temperature while the recording electric field is applied. This is then cooled to form recording magnetic domains on the recording layer Thus, depending on conditions such as the strength of the recording light and the material from which the recording layer is fashioned, it may happen that a delay occurs before the recording magnetic domains are actually formed on the recording layer, causing them to diverge from their prescribed positions according to the recording clock. On the other hand, the fact that the reproducing external magnetic field in MAMMOS is also based on a clock pit which is formed on the substrate means there is no guarantee that the external magnetic field is being applied in line with positions where recording magnetic domains actually exist. For this reason it proved to be no easy matter to adjust the modulation timing of the reproducing external magnetic field and reproducing light applied to a MAMMOS magneto-optical recording medium.
SUMMARY OF THE INVENTION
It is an object of the present invention, which has been designed to eliminate the problems inherent in the related art, to provide a magneto-optical recording medium capable of generating a reproducing clock in synchrony to a high degree of precision with the recording domain which is recorded on the information recording layer, and to provide a method of recording and reproducing same, and apparatus for recording and reproducing it. It is a further object of the present invention to provide a magneto-optical recording medium which permits easy adjustment of the optimum timing for applying reproducing light and reproducing electric field when reproducing a magneto-optical recording medium of the type wherein a reproducing magnetic field is applied along with the reproducing light, and to provide a method of recording and reproducing same, and apparatus for recording and reproducing it.
The first aspect of the present invention provides a magneto-optical recording medium comprising an information recording layer on which information is recorded; and a reproducing layer on to which information recorded on the information recording layer is transferred, a clock mark being formed on the information recording layer.
The magneto-optical recording medium according to the present invention has clock marks formed on the information recording layer along with information recording marks. This allows a reproducing clock to be generated in accordance with the clock marks. The following are two examples of methods which may be employed in order to detect the clock marks recorded on the information recording layer,
The first method of detection involves the use of two types of light of differing wavelengths &lgr;
1
and &lgr;
2
. The reproducing layer is reproduced by means of light of wavelength &lgr;
1
, while light of wavelength &lgr;
2
is used to read the clock marks recorded on the recording layer. The reason for using light of a different wavelength to read the reproducing clock marks is as follows. In MAMMOS and MSR there are reproducing and intermediate layers above the recording layer, so that light absorption by these layers serves to diminish the reproducing signal from the clock marks of the recording layer. What is more, the need to acquire the reproducing clocks in advance of information reproduction makes it difficult to use information reproducing light to reproduce the clock marks. The use of light of a different w
Awano Hiroyuki
Itou Akiyoshi
Nakagawa Katsuji
Ohta Norio
Sekine Masaki
Hitachi Maxell Ltd.
Neyzari Ali
Oliff & Berridg,e PLC
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