Magneto-optical disk system with specified thickness for protective layer on the disk relative to the numerical aperture of the objective lens

Abstract

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 t2 of the light-transmitting protective layer is set to fall within the range of 0.6 to <DEL-S DATE="20011030" ID="DEL-S-00001">1.0<DEL-E ID="DEL-S-00001"> <INS-S DATE="20011030" ID="INS-S-00001">0.1 <INS-E ID="INS-S-00001">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.

We claim:  
     
       1. An optical disc system for recording information signals and/or reproducing information signals comprising: 
       laser beam generating means;  
       an optical disc including a rigid  light- transmitting  substrate, a recording layer formed on one side of the light- transmitting  substrate and irradiated by a laser beam from said  the laser beam generating means through the light- transmitting substrate  during recording or reproduction, and a light-transmitting cover layer covering the recording layer and capable of transmitting the laser beam ; and  
       an objective lens for bundling or focusing the laser beam on the recording layer through the light-transmitting cover layer  substrate,  
       wherein said optical disc system is characterized in that the thickness of the light-transmitting cover layer  substrate of said  the optical disc falls within a range of 0.6 to 1.0  0.1 mm, and a numerical aperture of said  the objective lens falls within a range of 0.55 to 0.70.  
     
     
       2. A magneto-optical disc system for recording information signals and/or reproducing information signals comprising: 
       laser beam generating means for generating a laser beam;  
       a magneto-optical having  including a rigid  light- transmitting  substrate, a magneto-optical recording layer formed on the light- transmitting  substrate and irradiated by the laser beam from said  the laser beam generating means through the light- transmitting substrate  during recording and reproduction, and a light-transmitting cover layer covering the magneto-optical recording layer and capable of transmitting the laser beam ;  
       an objective lens for focusing the laser beam on the magneto-optical recording layer through said  the light-transmitting cover layer  substrate; and  
       magnetic field applying means for applying a magnetic field to the magneto-optical recording layer,  
       wherein said  the magneto-optical disc system is characterized in that the thickness of the light-transmitting cover layer  substrate of said  the magneto-optical disc falls within a range of 0.6 to 1.0  0.1 mm, and a numerical aperture of said  the objective lens falls within a range of 0.55 to 0.70.  
     
     
       3. A magneto-optical disc system according to claim  2 , wherein said magnetic field applying means and said objective lens are located on opposite sides of said magneto-optical disc so as to face each other. 
     
     
       4. A magneto-optical disc system according to claim  2 , wherein said magnetic field applying means is adjacent to said objective lens. 
     
     
       5. A magneto-optical disc system according to claim  4 , wherein said magnetic field applying means is positioned between said objective lens and said magneto-optical disc and faces said magneto-optical disc. 
     
     
       6. A magneto-optical disc system for recording and/or reproducing information signals comprising: 
       a magneto-optical disc including a rigid  an interconnecting substrate having two sides, each side of said  the interconnecting substrate having a magneto-optical recording layer formed thereon  and a light-transmitting cover layer formed on said recording layer to cover said recording layer  connected thereto; and  
       a pair of magneto-optical pickup units arranged on opposite sides of said  the magneto-optical disc so as to face each other with respect to the magneto-optical disc, each magneto-optical pickup unit includes:  
       laser beam generating means for generating a laser beam to said  the magneto-optical disc during recording and/or reproduction;  
       an objective lens for focusing said  the laser beam on said  the magneto-optical recording layer through said  the light-transmitting cover layer;  
       magnetic field applying means arranged near said  the objective lens to apply a magnetic field to said  the magneto-optical recording layer; , 
       wherein the thickness of said  the light-transmitting cover layer falls within a range of 0.6 to 1.0  0.1 mm, and the numerical aperture of said  the objective lens falls within a range of 0.55 to 0.70.  
     
     
       7. A magneto-optical disc system according to claim  6 , wherein said magnetic field applying means is located between said objective lens and said magneto-optical disc and faces said magneto-optical disc. 
     
     
       8. A magneto-optical disc system according to claim  4  or  6 , wherein said magnetic field applying means is formed with a coil pattern in a light-transmitting glass plate. 
     
     
       9. A magneto-optical disc system according to claim  2  or  6 , wherein said magneto-optical disc has a high-permeability layer between said substrate and said magneto-optical recording layer.