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.]. .Iadd.0.1 .Iaddend.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
Yoshio Tetsu
Aoki Watanabe