Optical pickup device

Abstract

An optical pickup device for condensing the light from a light source on a signal recording surface by an objective lens and for detecting the return light from the signal recording surface by a light detection unit is disclosed. The optical pickup device is capable of recording and/or reproducing at least two different sorts of optical recording media. The light beam radiated from a light source is condensed by an objective lens. An aperture varying unit varies the size of an aperture of the objective lens depending upon the sorts of the optical recording media. The return light from the optical recording medium is detected by a light detection unit. The size of the aperture of the objective lens for condensing the light from the light source is varied depending upon the difference in substrate thickness of the different sorts of the optical recording media, thus assuring high-quality recording/reproduction for two or more different sorts of optical recording media.

What is claimed is:  
     
       1. An optical pickup device capable of recording and/or reproducing at least two different sorts of optical recording media, comprising: 
       a light source radiating a light beam;  
       an objective lens for condensing the light from said light source;  
       substrate thickness detection means for detecting a thickness of a substrate of the optical recording medium;  
       aperture varying means for varying the size of an aperture of said objective lens depending upon an output signal from said substrate thickness detection means; and  
       light detection means for detecting the return light from said optical recording medium.  
     
     
       2. The optical pickup device as claimed in  claim 1 , wherein said optical recording media are an optical recording medium having a substrate thickness of 0.6 mm and an optical recording medium having a substrate thickness of 1.2 mm and wherein said aperture varying means sets a numerical aperture NA of said objective lens with respect to the optical recording medium having a substrate thickness of 0.6 mm to 0.6, while setting a numerical aperture NA o  of said objective lens with respect to the optical recording medium having a substrate thickness of 1.2 mm to: 
       
         
           NA o ≦(0.45/0.78)×λ o    
         
       
       where NA o  is a numerical aperture of said objective lens with respect to said optical recording medium having the substrate thickness of 1.2 mm and λ o  is a numerical value equal to the wavelength in μm of light radiated from said light source. 
     
     
       3. The optical pickup device as claimed in  claim 1  wherein said aperture varying means is arranged between said objective lens and said light source. 
     
     
       4. The optical pickup device as claimed in  claim 1  wherein said aperture varying means is arranged between said objective lens and said optical recording medium. 
     
     
       5. The optical pickup device as claimed in  claim 1  wherein said aperture varying means is arranged on the surface of said objective lens. 
     
     
       6. The optical pickup device as claimed in  claim 1  wherein said aperture varying means is arranged within the inside of said objective lens. 
     
     
       7. The optical pickup device as claimed in  claim 1  wherein said aperture varying means varies the aperture size by rotating respective blades of a light stop mechanism having a plurality of blades. 
     
     
       8. The optical pickup device as claimed in  claim 1  wherein said aperture varying means varies the aperture size using a liquid crystal shutter. 
     
     
       9. The optical pickup device as claimed in  claim 1  wherein said aperture varying means varies the aperture size by moving a plate having plural openings for changing over said openings. 
     
     
       10. An optical pickup device capable of recording and/or reproducing optical recording media, comprising: 
       
         a light source radiating a light beam;  
       
       
         an objective lens for condensing the light from said light source;  
       
       
         a liquid crystal shutter arranged in an optical path between the light source and said objective lens, which is operative to electrically change at least a size of a light beam passing said liquid crystal shutter;  
       
       
         a substrate thickness detection means for detecting a substrate thickness of the optical recording media which is loaded; and  
       
       
         liquid crystal control means for controlling said liquid control shutter to minimize the wave front aberration of a beam spot converged onto said optical recording media in accordance with the result of the substrate thickness detection means. 
       
     
     
       11. The optical pickup device as claimed in  claim 10 , further comprising light detection means for detecting a return light from said optical recording media, and said substrate thickness detection means detects a difference in substrate thickness using RF or servo signals detected by said light detection means. 
     
     
       12. The optical pickup device as claimed in  claim 10 , wherein the substrate thickness detection means detects a difference in substrate thickness using information regarding substrate thickness recorded on said optical recording media. 
     
     
       13. A wave front aberration compensating apparatus for an optical data recording and reproducing apparatus to correct a wavefront aberration of light emitted from a light source and converged onto a data recording medium through an image forming optical system, said apparatus comprising: 
       
         a liquid crystal shutter arranged in an optical path between the light source and said data recording medium, which is operative to electrically change at least a size of a light beam passing said liquid crystal shutter;  
       
       
         a substrate thickness detection means for detecting a substrate thickness of the data recording medium which is loaded; and  
       
       
         liquid crystal control means for controlling the liquid crystal shutter to minimize the wave front aberration of a beam spot converged onto said data recording medium in accordance with the result of the substrate thickness detection means. 
       
     
     
       14. The wave front aberration compensating apparatus as claimed in  claim 13 , further comprising light detection means for detecting a return light from said data recording medium, and said substrate thickness detection means detects a difference in substrate thickness using RF or servo signals detected by the light detection means. 
     
     
       15. The wave front aberration compensating apparatus as claimed in  claim 13 , wherein the substrate thickness detection means detects the difference in substrate thickness using information regarding substrate thickness recorded on the data recording medium.