Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2001-10-10
2004-08-24
Dinh, Tan (Department: 2652)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013330
Reexamination Certificate
active
06781926
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magneto-optical recording apparatus for recording information on a magneto-optical recording medium with an objective lens having high NA. The present invention also relates to a magneto-optical head to be used for the magneto-optical recording apparatus.
2. Related Art
In recent years, in response to the advance of multimedia, the optical recording medium has been used, on which a large amount of data can be recorded at a high density, and recording and reproduction can be performed at a high speed. Such an optical recording medium includes read-only media such as compact disks on which information is previously recorded as pits on the disk during formation of the disk, write-once media such as CD-R on which recording can be performed only once, and rewritable media on which data can be rewritten any number of times by the magneto-optical recording system or the phase-change recording system.
Among the optical recording media as described above, a magneto-optical recording medium is principally used in a field in which a high transfer rate is required. When the magneto-optical recording medium is subjected to recording and reproduction, a laser beam is converged with a lens up to the diffraction limit so that the magneto-optical recording medium is irradiated therewith. The light spot, which is formed on the magneto-optical recording medium as a result of the irradiation with the laser beam, has a size of about &lgr;/NA provided that &lgr; represents the wavelength of the laser beam and NA represents the numerical aperture of the lens.
In order to record or reproduce a pattern having a higher density, i.e., having a smaller size, it is necessary to use a smaller laser beam spot. In order to decrease the size of the light spot, it is conceived that the wavelength (&lgr;) of the laser beam is decreased or the numerical aperture (NA) of the lens is increased according to the expression described above. The numerical aperture (NA) of the lens is represented by NA=sin &thgr; provided that &thgr; represents the focusing half angle of the lens, and numerical aperture (NA) of the lens has a value smaller than 1. The objective lens, which is used in an optical recording apparatus commercially available at present, has NA of about 0.6 at most. The reason why the value of NA is restricted to be about 0.6 is as follows. That is, if the NA is increased, the astigmatism and the aberration generated when the optical axis of the objective lens is inclined with respect to the disk surface are increased. In order to solve this problem, it is necessary to thin the thickness of the transparent substrate of the disk through which the light beam is transmitted before arrival at the magneto-optical recording layer of the magneto-optical recording medium. However, if the thickness of the substrate is made thin, then the surface fluctuation of the disk is increased due to the decrease in rigidity of the substrate, and the substrate is inclined with respect to the optical axis of the objective lens. For this reason, the aberration as described above is generated.
In view of the above, it is conceived that the light beam is allowed to come into the disk from the side opposite to the substrate of the disk, i.e., from the side of the film surface, when the disk is irradiated with the light beam. Even if the film surface incidence system is adopted as described above, various problems still remain when the objective lens having high NA is used.
For example, a magneto-optical head, in which an optical system and a magnetic coil are integrated into one unit, is known to be used in a magneto-optical recording apparatus. Such a magneto-optical head is effective when information is recorded in the magneto-optical recording layer by using a lens having high NA. However, the magnetic characteristics are deteriorated especially when the recording is performed by applying a modulated magnetic field having a high frequency, because the magnetic coil is heated by the radiated light beam. Japanese Patent Application Laid-Open No. 11-316986 discloses an optical head which is provided with a thermal conduction film between a coil and a coil support member. This patent document discloses the following technique. That is, the thermal conduction film has a coefficient of thermal conductivity which is not less than at least several times a coefficient of thermal conductivity of the coil support member. Therefore, the heat, which is generated in the coil, can be efficiently conducted to an objective lens via the thermal conduction film to suppress the increase of temperature of the coil. However, if the heat is conducted to the objective lens, a problem arises such that the optical characteristics of the lens are deteriorated due to the thermal expansion of the lens.
Usually, the magneto-optical head includes two types of lenses which are provided in combination to be used as an objective lens system. When the lenses each having high NA are used for the objective lenses, the wave front aberration readily tends to appear due to any discrepancy between the optical axes of the lenses. The wave front aberration as described above decreases the reproduced signal characteristics. Therefore, it is necessary that the optical axes of the two types of the lenses of the objective lens system are mutually adjusted highly accurately.
SUMMARY OF THE INVENTION
The present invention has been made in order to solve the problems involved in the conventional technique as described above, a first object of which is to provide a magneto-optical head and a magneto-optical recording apparatus based on the use of the magneto-optical head which makes it possible to effectively release heat from a coil without deteriorating the optical characteristics of an objective lens.
A second object of the present invention is to provide a magneto-optical head and a magneto-optical recording apparatus based on the use of the magneto-optical head which makes it possible to effectively avoid any occurrence of aberration by highly accurately adjusting optical axes of two lenses which construct an objective lens system of the magneto-optical head.
According to a first aspect of the present invention, there is provided a magneto-optical head to be used for recording information on an information-recording medium, comprising:
a lens which collects a light beam onto the information-recording medium;
a substrate which has a first surface and a second surface parallel to one another and which supports the lens on the first surface;
a magnetic coil which is provided on the second surface of the substrate; and
a heat-releasing member which is provided on the second surface of the substrate and which releases heat generated by the magnetic coil.
In the magneto-optical head according to the present invention, the heat-releasing member is provided on the second surface. Accordingly, even when the magnetic coil is heated by the radiation of the light beam, the heat is not released to the first surface side of the substrate on which the lens is provided. Therefore, it is possible to avoid the thermal expansion of the lens, especially of the objective lens having high NA of 0.6≦NA, and it is possible to appropriately maintain the optical characteristics of the lens. On the other hand, the heat-releasing member, which is provided on the second surface, makes it possible to release the heat generated by the magnetic coil and the vicinity thereof, to the space between the magneto-optical head and the information-recording medium. Especially, the information-recording medium usually makes the rotating movement at a linear velocity of not less than 1 m/s with respect to the magneto-optical head. Therefore, the heat-releasing member is efficiently cooled by the air stream which is generated by the rotating movement.
In the present invention, it is desirable that the heat-releasing member is provided at a position which is nearer to the information-recording medium as compared with the
Awano Hiroyuki
Ishizaki Osamu
Maro Tsuyoshi
Shimazaki Katsusuke
Sugiyama Toshinori
Dinh Tan
Hitachi Maxell Limited
Oliff & Berridg,e PLC
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