Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse...
Reexamination Certificate
1997-11-21
2001-03-20
Neyzari, Ali (Department: 2651)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
C360S114050
Reexamination Certificate
active
06205092
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magneto-optic recording medium reproduction device, and more specifically to that employs near-field light and domain expansion.
2. Description of the Background Art
Magneto-optic recording medium has been noted as a highly reliable recording medium with rewritability and high storage capacity and has been put to practical use as the memory for computer and the like. However, further high density recording and reproducing technique has been sought for as the amount of information is further increased and the device is further miniaturized.
High density recording and reproducing technique is constituted by medium technique and device technique. The former technique includes a narrowed pitch of medium, an improved resolution for reproduction by means of magnetic multilayered film, and the like. The technique by means of magnetic multilayered film employs the fact that the intensity of laser spot forms Gaussian distribution to selectively transfer the magnetized state of a recording layer to a reproducing layer and read the magnetized state of the reproducing layer, and at present mainly has the three types of FAD (Front Aperture Detection), RAD (Rear Aperture Detection) and CAD (Center Aperture Detection). According to these techniques, the front or rear side or the vicinity of the center of a laser spot serves as a reproduction aperture to reduce the substantial diameter of a laser spot and thus increase reproduction density. The latter technique includes optical super-resolution technique for obtaining a condensation spot which exceeds the diffraction limit of laser beam, reduction in wavelength of laser beam and the like. Furthermore, near-field light recording and reproducing technique is provided for positioning one end surface of an optical fiber adjacent to a magneto-optic recording medium and irradiating the magneto-optic recording medium with laser beam from the optical fiber to record and reproduce signals. This technique allows formation of a recording domain of approximately 0.06 &mgr;m.
For reproduction by near-field light recording and producing technique, however, the reproduced signals which are detected are small due to the small domain, sufficient C/N ratio cannot be obtained, and reproduced signals are disadvantageously lost.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a magneto-optic recording medium reproduction device capable of accurately reproducing a signal recorded in a small domain, and a method of reproducing the same.
Another object of the present invention is to provide a magneto-optic recording medium suitable for the reproduction device and reproduction method mentioned above.
According to one aspect of the present invention, a magneto-optic recording medium reproduction device for reproducing a signal from a magneto-optic recording medium with a recording layer and a reproducing layer includes a laser device, an optical device, a detector and a magnetic field application device. The laser device oscillates laser beam. The optical device has an end surface adjacent to the magneto-optic recording medium, and irradiates the magneto-optic recording medium with the laser beam from the laser device via the end surface and receives the laser beam reflected from the magneto-optic recording medium via the end surface. The detector detects the laser beam received by the optical device. The magnetic field application device applies an alternating magnetic field to the magneto-optic recording medium to expand and shrink a domain created in the reproducing layer.
Preferably, the optical device includes an optical fiber which has a core, a first clad and a second clad. The core has a first refractive index. The first clad is formed around the core and has a second refractive index smaller than the first refractive index. The second clad is formed around the first clad and has a third refractive index smaller than the second refractive index.
Preferably, the optical device includes a first optical fiber and a second optical fiber. The first optical fiber has a first core and a first clad. The first core has a first diameter and a first refractive index. The first clad is formed around the first core and has a second refractive index smaller than the first refractive index. The second optical fiber has a second core and a second clad. The second core has a second diameter larger than the first diameter, and a third refractive index. The second clad is formed around the second core and has a fourth refractive index smaller than the third refractive index.
Preferably, the optical device a solid immersion lens, an objective lens and an optical system. The solid immersion lens has an end surface and a curved surface opposite to the end surface. The objective lens is arranged on the curved surface side of the solid immersion lens and is coaxial with the solid immersion lens. The optical system forms a first laser beam with a first diameter and a second laser beam with a second diameter larger than the first diameter coaxially incident on the objective lens.
Preferably the reproduction device further includes a diffraction grating element for transmitting the laser beam from the laser device straight and diffracting the laser beam received by the optical device towards the detector. The diffraction grating element further preferably includes a hologram.
According to another aspect of the present invention, a magneto-optic recording medium reproduction method for reproducing a signal from a magneto-optic recording medium having a recording layer and a reproducing layer magnetized in a predetermined direction includes the steps of: irradiating a magneto-optic recording medium with laser beam having a mixed intensity distribution of first and second intensity distributions each having a different beam diameter; applying an alternating magnetic field to the magneto-optic recording medium to expand and shrink a domain created in a reproducing layer when the magneto-optic recording medium is irradiated with the laser beam; and detecting a laser beam reflected from the magneto-optic recording medium.
Preferably, the step of detecting includes detecting the laser beam when a reproduced signal based on the intensity of the laser beam reflected from the magneto-optic recording medium is the greatest reproduced signal.
Still preferably, the step of detecting includes detecting the laser beam at the timing of applying a magnetic field in the direction opposite to the predetermined direction in which the reproducing layer is magnetized.
According to still another aspect of the present invention, a magneto-optic recording medium includes a substrate, a recording layer and a reproducing layer. The recording layer is positioned on the substrate and formed of a magnetic material. The reproducing layer is positioned on the recording layer and formed of a magnetic material.
The magneto-optic recording medium still preferably includes an intermediate layer positioned between the recording layer and the reproducing layer and formed of a non-magnetic material.
Preferably, minimum size of stable domain of the reproducing layer is larger than that of the recording layer.
The magneto-optic recording medium reproduction device is miniaturized since it uses an optical device having an end surface adjacent to the magneto-optic recording medium, rather than an objective lens, to irradiate the magneto-optic recording medium with laser beam. Furthermore, the reproduction device transfers a domain of the recording layer to the reproducing layer and expands the transferred domain size to reproduce a signal so that the intensity of the reproduced signal is improved and consequently a sufficient high C/N ratio can be obtained.
Furthermore, a so-called multi-clad, step index optical fiber is used as the optical device in the reproduction device to irradiate the magneto-optic recording medium with laser beam. Thus, the intensity of the beam spot is significantly increased onl
Sumi Satoshi
Suzuki Yoshihisa
Tanase Kenji
Yamaguchi Atsushi
Armstrong, Westerman Hattori, McLeland & Naughton
Neyzari Ali
Sanyo Electric Co,. Ltd.
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