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    • 4. 发明专利
    • OPTICAL HEAD DEVICE
    • CA2073321A1
    • 1993-01-09
    • CA2073321
    • 1992-07-07
    • TAKAHASHI AKIRAMURAKAMI YOSHITERUNAKAJIMA JUNSAKUOHTA KENJI
    • TAKAHASHI AKIRAMURAKAMI YOSHITERUNAKAJIMA JUNSAKUOHTA KENJI
    • G11B11/10G11B11/105G11B7/125
    • A magneto-optical disk (23) has a recording layer (4) whereon recorded bits are formed by the magnetic field modulation method and a readout layer (3) whose axis of easy magnetization is parallel to the recording layer (4) at room temperature, and varies to be perpendicular to the recording layer (4) within a predetermined temperature range between room temperature and the Curie temperature. During reproduction of recorded bits a first semiconductor laser (10) emits a heating-use light beam (7) to form the first light spot on the readout layer (3). Thus, a ring-shaped region corresponding to the predetermined temperature range exhibits perpendicular magnetic anisotropy and the recorded bits are copied from the recording layer onto the ring-shaped region. As the first light spot is shifted, the ring-shaped region as a readout window of recorded bits is also shifted. Further, the second semiconductor laser (11) emits a reproduction-use light beam (8) such that the second light spot is formed on the readout layer (3) to overlap the first light spot at a rear portion thereof. Consequently, only one recorded bit copied onto the rear portion of the ring-shaped region can be reproduced. Therefore, high-quality reproduction signals can be obtained from the magneto-optical disk (23) inspite of information high density information recording.
    • 7. 发明专利
    • REPRODUCING OPTICAL DEVICE FOR A MAGNETO-OPTICAL RECORDING MEDIUM
    • CA2037428A1
    • 1991-09-06
    • CA2037428
    • 1991-03-01
    • TAKAHASHI AKIRAMURAKAMI YOSHITERUNAKAJIMA JUNSAKUOHTA KENJI
    • TAKAHASHI AKIRAMURAKAMI YOSHITERUNAKAJIMA JUNSAKUOHTA KENJI
    • G11B11/105G11B7/00G11B11/10
    • A reproducing optical device for a magneto-optical recording medium related to the present invention having light sources that emit linearly polarized lights towards a magneto-optical recording medium, polarization directions of the linearly polarized lights being mutually orthogonal. A quarter wavelength plate disposed between the recording medium and the light sources converts each of the linearly polarized lights into right and left circularly polarized lights respectively. Corresponding to recorded information, the recording medium has magnetized sections that are magnetized in a perpendicularly upward and downward direction with respect to a medium surface. Moreover, the recording medium displays the property of circular dichroism. When the right circularly polarized light and the left circularly polarized light are reflected off the recording medium, a first and a second photodetector generate a first and a second reproduced signal respectively, based on variation in reflected light intensity of each of the circularly polarized lights. This variation corresponds to the upward and the downward magnetization directions of the magnetized sections and is due to the circular dichroism effect. There is a phase difference of half a cycle between the first and the second reproduced signal and the signals vary inversely with respect to each other. Consequently, disk noise is cancelled by differentially amplifying the first and the second reproduced signal, and an SN ratio of a reproduced signal thereby can be improved.