Magneto-optical disk system with specified thickness for protective layer relative to the numerical aperture of the objective lens
 A magneto-optical disc system includes a magneto-optical disc with a light-transmitting cover, an objective lens for bundling or focusing a laser beam on a magnetic recording layer of the magneto-optical disc in order to perform recording and/or reproduction, and a magnetic field generating unit obtained by forming a coil pattern in an optical glass. In the above system, the thickness t.sub.2 of the light-transmitting cover is set to fall within the range of 0.6 to 0.1 mm, and the numerical aperture (NA) 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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Tetsu Yoshio
Watanabe Aoki