Optical apparatus, tracking apparatus and optical disk apparatus

Abstract

An optical apparatus can eliminate offset resulting from assembling errors and also can correct offset even in the photodetector of any optical system. An optical disk apparatus for reading information from tracks traces the track with the condensed spot of light beam depending on the tracking error signal obtained from the optical system for tracking error detection. The tracking error detecting optical system includes an optical apparatus having a photodetector for outputting, as the tracking error signal, a differential value of outputs of a plurality of light receiving sections for receiving the light beam condensed by the condenser lens. Also, an optical element is provided for relatively increasing and/or decreasing the amount of receiving light of a light receiving section depending on displacement of the optical axis of the light beam, in order to balance the light received by the light receiving sections and compensate for affect.

What is claimed is:  
     
         1 . An optical apparatus for decoding information stored in a target comprising 
 a source of light,    a condenser lens through which the light passes, the condenser lens forming the light into a beam which has an optical axis,    the beam being sent to the target after the light passes through said condenser lens, the target encoding the light beam with the information and directing the encoded light beam to an optical detector,    said optical detector having a plurality of light receiving sections, each of which can receive at least a portion of the encoded light beam for purposes of aligning the light beam with the target, and    means for balancing the distribution of light in said light receiving sections if the optical axis of the light beam is displaced with respect to the light receiving sections when the light beam is aligned with the target.    
     
     
         2 . The optical apparatus of claim  1 wherein said balancing means comprises 
 an optical device through which the light beam passes before it is received by said optical detector, said optical detector having a circular-like region through which the light passes without substantial interference, said circular-like region having a diameter which is equal to or smaller than the diameter of said light beam,    said circular-like region further having at least first and second halves, wherein light passing through said first half is directed towards a first said light receiving section, and light which passes through said second half is directed to a second said light receiving section,    said optical device further having a first light directing device outside of said first half of said circular-like region which directs light to said second light receiving section, and    a second light directing device outside of said second half of said circular-like region which directs light to said first light receiving section.    
     
     
         3 . The optical apparatus of  claim 2  wherein said circular-like region is circular.  
     
     
         4 . The optical apparatus of  claim 2  wherein said first and second circular-like regions are formed of arcs having a radius which is greater than half the total width of said circular-like region, and an origin displaced from the center of said optical device.  
     
     
         5 . The optical apparatus of  claim 2  wherein said circular-like regions form an elliptical shape.  
     
     
         6 . The optical apparatus of  claim 2  wherein said first and second light directing devices are diffraction gratings.  
     
     
         7 . The optical apparatus of  claim 2  wherein said first and second light directing devices are prisms.  
     
     
         8 . The optical apparatus of  claim 2  wherein said first and second light directing devices are circular lenses.  
     
     
         9 . The optical apparatus of  claim 2  wherein said first and second halves are third and fourth light directing devices, said first and second halves of said optical detector being offset from said axis on different sides of said optical device.  
     
     
         10 . The optical apparatus of  claim 9  comprising a second optical detector, said optical device further having a fifth light directing device which directs part of said light beam to said second optical detector.  
     
     
         11 . The optical apparatus of  claim 10  wherein said third optical detector is offset with respect to said axis.  
     
     
         12 . The optical apparatus of  claim 11  wherein said light source, said optical detector and said second optical detector are mounted on a single substrate.  
     
     
         13 . The optical apparatus of  claim 11  wherein the target is a track in a track medium, said optical detector generates a tracking error signal, and said second optical detector generates a focus error signal.  
     
     
         14 . The optical apparatus of  claim 10  wherein said first, second, third, fourth and fifth are formed as a single thin plate type diffraction grating.  
     
     
         15 . The optical apparatus of  claim 2  comprising a shielding region in the circular-like regions.  
     
     
         16 . The optical apparatus of  claim 15  wherein said shielding region is opaque.  
     
     
         17 . The optical apparatus of  claim 15  wherein said shielding region is a diffraction grating.  
     
     
         18 . The optical apparatus of  claim 9  wherein said light source and said optical detector are mounted on a single substrate.  
     
     
         19 . The optical apparatus of  claim 1  wherein said balancing means comprises 
 an optical device through which the light beam passes before it is received by said optical detector, said optical device having a circular-like region through which the light passes, said circular-like region having a cross-sectional area which is equal to or smaller than the cross-sectional area of the light beam,  
 said circular-like region further having at least first and second halves, wherein light passing through said first half is directed towards a first said light receiving section, and light which passes through said second half is directed to a second said light receiving section, the paths of the light passing through said first and second halves crossing each other as they approach said optical detector,  
 said optical device further having a first light directing device outside of said first half of said circular-like region which directs light to said second light receiving section, and  
 a second light directing device outside of said second half of said circular-like region which directs light to said first light receiving section, the paths of the light passing through said first and second light directing devices not crossing each other as they approach said optical detector.  
 
     
     
         20 . The optical apparatus of  claim 19  wherein said first and said second halves of said circular-like region are conical prisms.  
     
     
         21 . The optical apparatus of  claim 19  wherein said first and said second halves of said circular-like region are third and fourth diffraction gratings.  
     
     
         22 . The optical apparatus of  claim 21  wherein said optical detector is offset with respect to said optical axis.  
     
     
         23 . The optical apparatus of  claim 1  wherein the target is a track in a disk medium.  
     
     
         24 . An optical apparatus for decoding information stored in a target comprising 
 a source of light,    a condenser lens through which the light passes, the condenser lens forming the light into a beam which has an optical axis,    the light beam being sent to the target after the light beam passes through said condenser lens, the target encoding the light beam with the information and directing the encoded light beam to an optical detector,    said optical detector having a plurality of light receiving sections to receive at least a portion of the encoded light for purposes of balancing the distribution of light in said light receiving sections if the optical axis of the light beam is displaced with respect to the light receiving sections when the light beam is aligned with the target.    
     
     
         25 . The optical apparatus of  claim 24  wherein said optical detector includes 
 a first light receiving section provided with a first semicircular-like region,  
 a second light receiving section provided with a second semicircular-like region, the first and second semicircular regions having a diameter equal to or smaller than the diameter of said light beam,  
 a third light receiving section formed adjacent the external side of said second light receiving section, and  
 a fourth light receiving section formed adjacent the external side of said first light receiving section,  
 said first and third light receiving sections being coupled so that their respective outputs are added together,  
 said second and fourth light receiving section being coupled so their respective outputs are added together,  
 whereby the distribution of light in said light receiving sections is balanced if the optical axis of the light beam is displaced with respect to the light receiving sections when the light beam is aligned with the target.