Magneto-optical disk system with specified thickness for protective layer on the disk relative to the numerical aperture of the objective lens
 A magneto-optical disc system includes a magneto-optical disc with a light transmitting protective layer, an objective lens for bundling or focusing a laser beam onto a magnetic recording layer of the magneto-optical disc in order to perform recording and/or reproduction, and a magnetic field generating unit formed as a coil pattern on a transparent optical glass layer. In the magneto-optical disc system, the thickness t.sub.2 of the light-transmitting protective layer is set to fall within the range of 0.6 to 1.0 mm and the numerical aperture of the objective lens is set to fall within the range of 0.55 to 0.70, so as to obtain high density recording and/or reproduction by permitting the lens to be quite close to the actual recording layer. 
Sony Corporation
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Yoshio Tetsu
Aoki Watanabe