Optical head

Abstract

In an optical disc recording-reproducing apparatus using a standard optical disc enclosed in a cartridge, and optical plate for correcting various aberrations generated by a focusing lens is comprised therein in order to allow use of a double recording optical disc enclosed in the standard cartridge of the same size, the optical plate is placed in front of a focusing lens when the double recording optical disc is used, and is removed from the front of the focusing lens when the standard optical disc is used.

What is claimed is:  
     
       1. An optical disc recording-reproducing apparatus comprising: 
       laser light emitting means for emitting laser light,  
       collimating means for collimating said laser light emitted by said laser light emitting means,  
       focusing means for focusing said laser light collimated by said collimating means on a recording  information area of a first optical disc having a first substrate of a first thickness (t 1 ) and a first refractive index (n 1 ) or a second optical disc having a second substrate of a second thickness (t 2 ) and a second refractive index (n 2 ),  
       a beam splitter for separating laser light reflected from said recording  information area of said first optical disc or said second optical disc,  
       laser light sensing means for detecting laser light separated by said beam splitter,  
       at least one optical plate for correcting aberration of said focusing means, having a thickness (t 3 ) equal to a difference (n 1 *t 1 −n 2 *t 2 ) between the product of said first refractive index (n 1 ) multiplied by said first thickness (t 1 ) and the product of said second refractive index (n 2 ) multiplied by said second thickness (t 2 ) divided by a refractive index (n 3 ) of said optical plate, and  
       actuator means for positioning said optical plate between said optical disc and said focusing means or for removing said optical plate therefrom.  
     
     
       2. An optical disc recording-reproducing apparatus in accordance with claim  1 , wherein 
       said optical disc is enclosed in a cartridge having at least one identification pit for identifying said optical disc enclosed in said cartridge, and said identifying pit being detected by a sensing means, the detected output of said sensing means being utilized to control said actuator means.  
     
     
       3. An optical disc recording-reproducing apparatus in accordance with claim  2 , wherein said sensing means includes a light source and a light sensing element. 
     
     
       4. An optical disc comprising: 
       a first substrate of at least a thickness of about 0.6 mm thick having a recording consisting essentially of a layer having a tracked surface and an information layer on one side thereof,  
       a second substrate of at least a thickness of about 0.6 mm thick having a recording consisting essentially of a layer having a tracked surface and an information layer on one side thereof, said second substrate being adhered to said first substrate with adhesive substance of at most 0.2 mm thick in a manner that the recording information layer of said second substrate is faced to the recording information layer of said first substrate, said adhesive forming a solid boundary between said first and second substrates.  
     
     
       5. The optical disc of claim  4  wherein the recording or erasing of at least one of said information layers is effected by changing the phase of said information layer. 
     
     
       6. The optical disc of claim  5  wherein said information layers are erased by crystallization of said information layers. 
     
     
       7. An optical disc comprising: 
       
         first and second substrates of a thickness of about  0 . 6  mm, an adhesive substance of at most  0 . 2  mm thick interposed between said first and second substrates, said adhesive forming a solid boundary between said first and second substrates, at least one of said first and second substrates consisting essentially of a layer having a tracked surface and having an information layer on one side thereof, said one side of said substrate having said information layer facing said other substrate. 
       
     
     
       8. A process for recording to or reproducing from optical discs of different substrate thicknesses comprising: 
       
         emitting laser light,  
       
       
         collimating the emitted laser light,  
       
         focusing the collimated laser light on an information area of a first optical disc having a first substrate of a thickness  ( t 1   )  and a first refractive index  ( n 1   )  or a second optical disc having a second substrate thickness  ( t 2   )  and a second refractive index  ( n 2   ) ,    
       
         separating the laser light reflected from said information area of said first optical disc or said second optical disc,  
       
       
         detecting the separated laser light,  
       
         correcting aberration of a focusing means using an optical plate having a thickness  ( t 3   )  equal to the difference  ( n 1 *t 1 −n 2 *t 2   )  between the product of said first refractive index  ( n 1   )  multiplied by said first thickness  ( t 1   )  and the product of said second refractive index  ( n 2   )  multiplied by said second thickness  ( t 2   )  divided by a refractive index  ( n 3   )  of said optical plate, and    
       
         positioning said optical plate between said optical disc and said focusing means. 
       
     
     
       9. An optical disc reproducing apparatus comprising: 
       
         laser light emitting means for emitting laser light,  
       
       
         collimating means for collimating said laser light emitted by said laser light emitting means,  
       
         focusing means for focusing said laser light collimated by said collimating means on an information area of a first optical disc having a first substrate of a thickness  ( t 1   )  and a first refractive index  ( n 1   )  or a second optical disc having a second substrate thickness  ( t 2   )  and a second refractive index  ( n 2   ) ,    
       
         a beam splitter for separating the laser light reflected from said information area of said first optical disc or said second optical disc,  
       
       
         laser light sensing means for detecting separated laser light,  
       
         at least one optical plate for correcting aberration of said focusing means using an optical plate having a thickness  ( t 3   )  equal to the difference  ( n 1 *t 1 −n 2 *t 2   )  between the product of said first refractive index  ( n 1   )  multiplied by said first thickness  ( t 1   )  and the product of said second refractive index  ( n 2   )  multiplied by said second thickness  ( t 2   )  divided by a refractive index  ( n 3   )  of said optical plate, and    
       
         actuator means for positioning said optical plate between said optical disc and said focusing means or for removing said optical plate therefrom. 
       
     
     
       10. An optical disc comprising: 
       
         a first substrate of a thickness of about  0 . 6  mm consisting essentially of a layer having an indented surface and an information layer on one side thereof,  
       
       
         a second substrate of a thickness of about  0 . 6  mm consisting essentially of a layer having an indented surface and an information layer on one side thereof, said second substrate being adhered to said first substrate with adhesive substance of at most  0 . 2  mm thick in a manner that the information layer of said second substrate is faced to the information layer of said first substrate, said adhesive forming a solid boundary between said first and second substrates. 
       
     
     
       11. An optical disc comprising: 
       
         a first substrate of a thickness of about  0 . 6  mm consisting essentially of a layer having a tracked surface and a reflective layer on one side thereof,  
       
       
         a second substrate of a thickness of about  0 . 6  mm consisting essentially of a layer having a tracked surface and a reflective layer on one side thereof, said second substrate being adhered to said first substrate with adhesive substance of at most  0 . 2  mm thick in a manner that the reflective layer of said second substrate is faced to the reflective layer of said first substrate, said adhesive forming a solid boundary between said first and second substrates. 
       
     
     
       12. An optical disc comprising: 
       
         a first substrate of a thickness of about  0 . 6  mm consisting essentially of a layer having an indented surface and a reflective layer on one side thereof,  
       
       
         a second substrate of a thickness of about  0 . 6  mm consisting essentially of a layer having an indented surface and a reflective layer on one side thereof, said second substrate being adhered to said first substrate with adhesive substance of at most  0 . 2  mm thick in a manner that the reflective layer of said second substrate is faced to the reflective layer of said first substrate, said adhesive forming a solid boundary between said first and second substrates.  
       
     
     
       13. An optical disc comprising: 
       
         first and second substrates of a thickness of about  0 . 6  mm, an adhesive substance of at most  0 . 2  mm thick interposed between said first and second substrates, said adhesive forming a solid boundary between said first and second substrates, at least one of said first and second substrates consisting essentially of a layer having an indented surface and having an information layer on one side thereof, said one side of said substrate having said information layer facing said other substrate.  
       
     
     
       14. An optical disc comprising: 
       
         first and second substrates of a thickness of about  0 . 6  mm, an adhesive substance of at most  0 . 2  mm thick interposed between said first and second substrates, said adhesive forming a solid boundary between said first and second substrates, at least one of said first and second substrates consisting essentially of a layer having a tracked surface and having a reflective layer on one side thereof, said one side of said substrate having said reflective layer facing said other substrate.  
       
     
     
       15. An optical disc comprising: 
       
         first and second substrates of a thickness of about  0 . 6  mm, an adhesive substance of at most  0 . 2  mm thick interposed between said first and second substrates, said adhesive forming a solid boundary between said first and second substrates, at least one of said first and second substrates consisting essentially of a layer having an indented surface and having a reflective layer on one side thereof, said one side of said substrate having said reflective layer facing said other substrate.  
       
     
     
       16. An optical disc comprising: 
       
         a first substrate of a thickness of about  0 . 6  mm consisting essentially of a layer having a tracked surface and an information layer on one side thereof,  
       
       
         a second substrate of a thickness of about  0 . 6  mm consisting essentially of a layer having a tracked surface and an information layer on one side thereof, said second substrate being adhered to said first substrate with adhesive substance of at most  0 . 2  mm thick in a manner that the information layer of said second substrate is faced to the information layer of said first substrate, wherein the information layer is a phase change material, said adhesive forming a solid boundary between said first and second substrates.  
       
     
     
       17. An optical disc comprising: 
       
         first and second substrates of a thickness of about  0 . 6  mm, an adhesive substance of at most  0 . 2  mm thick interposed between said first and second substrates, said adhesive forming a solid boundary between said first and second substrates, at least one of said first and second substrates consisting essentially of a layer having a tracked surface and having an information layer on one side thereof, said one side of said substrate having said information layer facing said other substrate, wherein the information layer is a phase change material. 
       
     
     
       18. An optical disc comprising: 
       
         a first substrate of a thickness of about  0 . 6  mm consisting essentially of a layer having an indented surface and an information layer on one side thereof,  
       
       
         a second substrate of a thickness of about  0 . 6  mm consisting essentially of a layer having an indented surface and an information layer on one side thereof, said second substrate being adhered to said first substrate with adhesive substance of at most  0 . 2  mm thick in a manner that the information layer of said second substrate is faced to the information layer of said first substrate, wherein the information layer is a phase change material, said adhesive forming a solid boundary between said first and second substrates.  
       
     
     
       19. An optical disc comprising: 
       
         first and second substrates of a thickness of about  0 . 6  mm, an adhesive substance of at most  0 . 2  mm thick interposed between said first and second substrates, said adhesive forming a solid boundary between said first and second substrates, at least one of said first and second substrates consisting essentially of a layer having an indented surface and having an information layer on one side thereof, said one side of said substrate having said information layer facing said other substrate, wherein the information layer is a phase change material.