Optical disc recording/reproduction apparatus and method

Abstract

An optical disc recording/reproduction apparatus for recording and/or reproducing a data by applying a beam from an optical head unit through a substrate onto/from a recording layer of the optical disc through, wherein the substrate of the optical disc is 0.3 mm or below; the optical head unit comprises: an objective lens for converging an incident beam and emitting the beam toward the optical disc; a forward lens for converging the beam introduced through the objective lens and applying the beam to the optical disc; a lens holder where the objective lens and the forward lens are fixed; and an actuator for driving the objective lens and the forward lens as a unitary block and controlling at least focusing, the objective lens and the forward lens having a total numerical aperture of 0.8 or above.

1. An optical disc recording/reproduction apparatus for recording and/or reproducing data by applying a beam from an optical head unit through a substrate of an optical disc onto/from a recording layer of the optical disc, wherein said substrate of said optical disc has a thickness of 0.3 mm or below, and said optical head unit comprises:
 an objective lens for converging an incident beam and emitting the beam toward said optical disc;  
 a forward lens for converging the beam introduced through said objective lens and applying the beam to said optical disc;  
 a lens holder in which said objective lens and said forward lens are fixed; and  
 an actuator for driving said objective lens and said forward lens as a unitary block and controlling at least focusing,  
 said objective lens and said forward lens having (1) a total numerical aperture of 0.8 or above, (2) a center position shift tolerance of ±80 μm, (3) an assembly accuracy of a distance between the objective lens and the forward lens of ±25 μm or less , and (4) inclination angles less than 0.4°.  
 
     
     
       2. An optical disc recording/reproduction apparatus as claimed in  claim 1 , wherein said forward lens and said substrate define a working distance of 50 μm to 500 μm. 
     
     
       3. An optical disc recording/reproduction apparatus as claimed in  claim 1 , wherein said forward lens and said objective lens have aspherical surfaces into/from which said beam is introduced. 
     
     
       4. An optical disc recording/reproduction apparatus as claimed in  claim 1 , wherein said forward lens and said objective lens are fixed at a predetermined distance in said lens holder. 
     
     
       5. An optical disc recording/reproduction apparatus as claimed in  claim 1 , wherein said actuator carries out tracking control of said forward lens and said objective lens. 
     
     
       6. An optical disc recording/reproduction apparatus as claimed in  claim 1 , said apparatus further comprises a magnetic head for applying a magnetic field to said recording layer of said optical disc. 
     
     
       7. An optical disc recording/reproduction method for applying a beam from an optical head having an objective lens for converging and emitting the beam toward an optical disc and a forward lens for converging the beam from said objective lens and emitting the beam to a recording layer through a substrate of said optical disc so as to record or reproduce data onto/from said recording layer, wherein
 said objective lens and said forward lens are fixed in a holder and are driven as a unitary block for focus control and said substrate of said optical disc a thickness of 0.3 mm or below, and  
 said objective lens and said forward lens have (1) a total numerical aperture of 0.8 or above, (2) a center position shift tolerance of ±80 μm, (3) an assembly accuracy of a distance between the objective lens and the forward lens of ±25 μm or less , and (4) inclination angles less than 0.4°.  
 
     
     
       8. An optical head unit for applying a beam through a substrate to a recording layer of an optical disc so as to record and/or reproduce data onto/from said recording layer, said optical head unit comprising:
 a first lens for converging an incoming beam and emitting the beam toward said optical disc;  
 a second lens for converging the beam emitted from said first lens and emitting the beam to said optical disc;  
 a lens holder in which said first lens and said second lens are fixed at a predetermined distance; and  
 an actuator for driving said lens holder so as to carry out at least focus control,  
 wherein said first lens and said second lens have (1) a total numerical aperture of 0.8 or above, (2) a center position shift tolerance of ±80 μm, (3) an assembly accuracy of a distance between the first lens and the second lens of ±25 μm or less , and (4) inclination angles less than 0.4°.  
 
     
     
       9. An optical head unit as claimed in  claim 8 , wherein said second lens and said substrate define a working distance of 50 μm to 500 μm. 
     
     
       10. An optical head unit as claimed in  claim 8 , wherein said first lens and said second lens have aspherical surfaces from/to which said beam is introduced. 
     
     
       11. An optical head unit as claimed in  claim 8 , wherein said actuator drives said lens holder for carrying out tracking control.