Magneto-optical recording and reproducing apparatus and method

Abstract

A magneto-optic recording medium reproduction device includes a multi-clad, step index optical fiber, a semiconductor laser arranged on one end surface side of the optical fiber for providing laser beam to one end surface of the optical fiber, a photodetector arranged on one end surface side of the optical fiber and receiving laser beam from one end surface of the optical fiber, and a magnetic head for applying an alternating field to the magneto-optic recording medium. Since the other end surface of the optical fiber is arranged adjacent to the magneto-optic recording medium, an accurate signal can be reproduced even from an extremely small recorded domain. Furthermore, since an alternating field is applied to the magneto-optic recording medium, a domain transferred from a recording layer of the magneto-optic recording medium to a reproducing layer is expanded and a large reproduced signal can be obtained from the expanded domain.

What is claimed is:  
     
         1 . A magneto-optic recording medium reproduction device for reproducing a signal from a magneto-optic recording medium with a recording layer and a reproducing layer, comprising: 
 laser means for oscillating a laser beam;    optical means having an end surface adjacent to said magneto-optic recording medium, for irradiating said magneto-optic recording medium with the laser beam from said laser means via said end surface and receiving a laser beam reflected from said magneto-optic recording medium via said end surface;    detection means for detecting the laser beam received by said optical means; and    magnetic field application means for applying an alternating field to said magneto-optic recording medium to expand and shrink a domain created in said reproducing layer.    
     
     
         2 . The magneto-optic recording medium reproduction device according to    claim 1   , wherein said optical means includes an optical fiber including: 
 a core having a first refractive index;    a first clad formed around said core and having a second refractive index smaller than said first refractive index; and    a second clad formed around said first clad and having a third refractive index smaller than said second refractive index.    
     
     
         3 . The magneto-optic recording medium reproduction device according to    claim 1   , wherein said optical means includes: 
 a first optical fiber including a first core having a first diameter and a first refractive index, and a first clad formed around said first core and having a second refractive index smaller than said first refractive index; and    a second optical fiber including a second core having a second diameter larger than said first diameter and a third refractive index, and a second clad formed around said second core and having a fourth refractive index smaller than said third refractive index.    
     
     
         4 . The magneto-optic recording medium reproduction device according to    claim 1   , wherein said optical means includes: 
 a solid immersion lens having said end surface and a curved surface opposite to said end surface;    an objective lens arranged on a said curved surface side of said solid immersion lens, coaxial with said solid immersion lens; and    an optical system forming first laser beam with a first diameter and a second laser beam with a second diameter larger than said first diameter and allowing said first and second laser beams coaxially incident on said objective lens.    
     
     
         5 . The magneto-optic recording medium reproduction device according to    claim 4   , wherein: 
 said laser means includes    a first laser, and    a second laser; and    said optical system includes    a first lens forming said first laser beam, based on a laser beam from said first laser,    a second lens forming said second laser beam, based on a laser beam from said second laser, and    an optical mixing element for mixing said first laser beam and said second laser beam.    
     
     
         6 . The magneto-optic recording medium reproduction device according to    claim 4   , wherein: 
 said laser means includes one laser; and    said optical system includes    an optical splitting element for splitting a laser beam from said laser into two laser beams,    a first lens forming said first laser beam, based on one laser beam split from the laser beam by said optical splitting element,    a second lens forming said second laser beam, based on the other laser beam split from the laser beam by said optical splitting element, and    an optical mixing element for mixing said first laser beam and said second laser beam.    
     
     
         7 . The magneto-optic recording medium reproduction device according to    claim 1   , further comprising diffraction means for transmitting a laser beam from said laser means straight and diffracting a laser beam received by said optical means towards said detection means.  
     
     
         8 . The magneto-optic recording medium reproduction device according to    claim 7   , wherein said diffraction means includes a hologram.  
     
     
         9 . A magneto-optic recording medium reproduction device for reproducing a signal from a magneto-optic recording medium with a recording layer and a reproducing layer, comprising: 
 an optical fiber having one end surface adjacent to said magneto-optic recording medium and the other end surface;    a laser arranged on the other end surface side of said optical fiber for providing a laser beam to the other end surface of said optical fiber;    a photodetector arranged on the other end surface side of said optical fiber and receiving a laser beam from the other end surface of said optical fiber; and    a magnetic head arranged for applying an alternating field to said magneto-optic recording medium to expand and shrink a domain created in said reproducing layer.    
     
     
         10 . The magneto-optic recording medium reproduction device according to    claim 9   , wherein said optical fiber includes: 
 a core having a first refractive index;    a first clad formed around said core and having a second refractive index smaller than said first refractive index; and    a second clad formed around said first clad and having a third refractive index smaller than said second refractive index.    
     
     
         11 . A magneto-optic recording medium reproduction device for reproducing a signal from a magneto-optic recording medium with a recording layer and a reproducing layer, comprising: 
 a first optical fiber having one end surface adjacent to said magneto-optic recording medium and the other end surface;    a laser arranged on the other end surface side of said first optical fiber for providing a laser beam to the other end surface of said first optical fiber;    a second optical fiber having one end surface adjacent to said magneto-optic recording medium and the other end surface;    a photodetector arranged on the other end surface side of said second optical fiber and receiving a laser beam from the other end surface of said second optical fiber; and    a magnetic head arranged for applying an alternating field to said magneto-optic recording medium to expand and shrink a domain created in said reproducing layer.    
     
     
         12 . The magneto-optic recording medium reproduction device according to    claim 11   , wherein: 
 said first optical fiber includes    a first core having a first diameter and a first refractive index, and a first clad formed around said first core and having a second refractive index smaller than said first refractive index; and    said second optical fiber includes    a second core having a second diameter larger than said first diameter and a third refractive index, and    a second clad formed around said second core and having a fourth refractive index smaller than said third refractive index.    
     
     
         13 . A magneto-optic recording medium reproduction device for reproducing a signal from a magneto-optic recording medium with a recording layer and a reproducing layer, comprising: 
 a solid immersion lens having a plane adjacent to said magneto-optic recording medium and a curved surface opposite to said plane;    an objective lens arranged on the curved surface side of said solid immersion lens, coaxial with said solid immersion lens;    a laser;    an optical system for forming from a laser beam from said laser a first laser beam with a first diameter and a second laser beam with a second diameter larger than said first diameter and allowing said first and second laser beams coaxially incident on said objective lens;    a photodetector receiving a laser beam reflected from said magneto-optic recording medium and transmitted through said solid immersion lens and said objective lens; and    a magnetic head arranged for applying an alternating field to said magneto-optic recording medium to expand and shrink a domain created in said reproducing layer.    
     
     
         14 . A magneto-optic recording medium reproduction device for reproducing a signal from a magneto-optic recording medium with a recording layer and a reproducing layer, comprising: 
 a solid immersion lens having a plane adjacent to said magneto-optic recording medium and a curved surface opposite to said plane;    an objective lens arranged on the curved surface side of said solid immersion lens, coaxial with said solid immersion lens;    a first laser;    a first lens forming a first laser beam with a first diameter, based on a laser beam from said first laser;    a second lens forming a second laser beam with a second diameter larger than said first diameter, based on a laser beam from said second laser;    an optical system for allowing said first and second laser beams coaxially incident on said objective lens;    a photodetector receiving a laser beam reflected from said magneto-optic recording medium and transmitted through said solid immersion lens and said objective lens; and    a magnetic head arranged for applying an alternating field to said magneto-optic recording medium to expand and shrink a domain created in said reproducing layer.    
     
     
         15 . A magneto-optic recording medium reproduction method for reproducing a signal from a magneto-optic recording medium having a recording layer and a reproducing layer magnetized in a predetermined direction, comprising the steps of: 
 irradiating said magneto-optic recording medium with a laser beam having a mixed intensity distribution of first and second intensity distributions different in beam diameter;    applying an alternating field to said magneto-optic recording medium to expand and shrink a domain created in said reproducing layer when said magneto-optic recording medium is irradiated with said laser beam; and    detecting a laser beam reflected from said magneto-optic recording medium.    
     
     
         16 . The magneto-optic recording medium reproduction method according to    claim 15   , wherein said step of detecting includes detecting said laser beam when a reproduced signal based on an intensity of the laser beam reflected from said magneto-optic recording medium is a greatest reproduced signal.  
     
     
         17 . The magneto-optic recording medium reproduction method according to    claim 16   , wherein said step of detecting includes detecting said laser beam when a magnetic field is applied in a direction opposite to said predetermined direction.  
     
     
         18 . A magneto-optic recording medium reproduction method for reproducing a signal from a magneto-optic recording medium having a recording layer and a reproducing layer magnetized in a predetermined, first direction, comprising the steps of: irradiating said magneto-optic recording medium with a laser beam having an intensity distribution with a first diameter of beam to transfer a domain in said recording layer to said reproducing layer; 
 applying a magnetic field to said magneto-optic recording medium in a second direction opposite to said first direction to expand a domain transferred to said reproducing layer;    irradiating said magneto-optic recording medium with a laser beam having an intensity distribution with a second diameter of beam larger than said first diameter of beam;    detecting a laser beam reflected from said magneto-optic recording medium when said magneto-optic recording medium is irradiated with the laser beam having the intensity distribution with said second diameter of beam; and    applying a magnetic field to said magneto-optic recording medium in said first direction to shrink said expanded domain in said reproducing layer.    
     
     
         19 . A magneto-optic recording medium, comprising: 
 a substrate;    a recording layer positioned on said substrate and formed of a magnetic material; and    a reproducing layer positioned on said recording layer and formed of a magnetic material.    
     
     
         20 . The magneto-optic recording medium according to    claim 19   , further comprising an intermediate layer positioned between said recording layer and said reproducing layer and formed of a non-magnetic material.  
     
     
         21 . The magneto-optic recording medium according to    claim 19   , wherein a minimum size of stable domain of said reproducing layer is larger than a minimum size of stable domain of said recording layer.