Optical device

Abstract

An optical device includes a light-emitting element for irradiating light onto an information recording medium, a diffraction grating for splitting light emitted from said light-emitting element into a plurality of beams, a focussing member for focussing the plurality of beams onto the information recording medium, a deflection member for deflecting the plurality of beams after they have been reflected from the information recording medium; and a photodetector for receiving the plurality of beams after they have been deflected by the deflection member. The diffraction grating has a first grating region and a second grating region, which have different diffraction efficiencies. The zero-order diffraction light in the first grating region is used as the main beam for reproducing the information signal, and the +1-order or −1-order diffraction light in the second grating regions is used as sub-beams for reproduction of the tracking error signal. Thus, the light amount of both the main beam and the sub-beams can be increased without increasing the light emission of the semiconductor laser element 1, and the S/N ratio of the main beam and the sub-beams can be enhanced.

What is claimed is:  
     
         1 . An optical device comprising: 
 a light-emitting element;    a diffraction grating for splitting light emitted from said light-emitting element into a plurality of beams, the diffraction grating comprising a first grating region and a second grating region with a diffraction efficiency that is different from a diffraction efficiency of the first grating region; and    a focussing member for focussing light that has passed through the diffraction grating.    
     
     
         2 . An optical device comprising: 
 a light-emitting element for irradiating light onto an information recording medium;    a diffraction grating for splitting light emitted from said light-emitting element into a plurality of beams, the diffraction grating comprising a first grating region and a second grating region with a diffraction efficiency that is different from a diffraction efficiency of the first grating region;    a focussing member for focussing the beams that have been split by the diffraction grating on the information recording medium;    a deflection member for deflecting the plurality of beams after they have been reflected from the information recording medium; and    a photodetector for receiving the plurality of beams after they have been deflected by the deflection member.    
     
     
         3 . The optical device of  claim 1  or  2 , wherein a diffraction grating depth in the first grating region is different from a diffraction grating depth in the second grating region.  
     
     
         4 . The optical device of  claim 1  or  2 , wherein a diffraction grating depth in the first grating region and/or a diffraction grating depth in the second grating region changes stepwise with a constant period.  
     
     
         5 . The optical device of  claim 1  or  2 , wherein a diffraction grating in the first grating region and/or a diffraction grating in the second grating region is a blazed grating.  
     
     
         6 . The optical device of  claim 1  or  2 , wherein the diffraction grating pattern in the first grating region is different from the diffraction grating pattern in the second grating region.  
     
     
         7 . The optical device of  claim 1  or  2 , wherein a diffraction efficiency of zero-order diffraction light in the first grating region is larger than a diffraction efficiency of zero-order diffraction light in the second grating region.  
     
     
         8 . The optical device of  claim 2 , wherein 
 the zero-order diffraction light in the first grating region is used as a main beam for recording/reproducing an information signal on/from the information recording medium;    +1-order and/or −1-order diffraction light in the second grating region is used as a sub-beam for detecting a tracking error signal; and    the entire sub-beam passes through the second grating region.    
     
     
         9 . The optical device of  claim 1  or  2 , wherein 
 the first grating region is stripe-shaped; and  
 the grating in the first grating region and the grating in the second grating region are parallel to the first grating region.  
 
     
     
         10 . The optical device of  claim 1  or  2 , wherein 
 the first grating region is stripe-shaped; and  
 the grating in the first grating region and/or the grating in the second grating region is tilted by a predetermined angle with respect to the first grating region.  
 
     
     
         11 . An optical device, comprising: 
 a light-emitting element;    a diffraction grating for splitting light emitted from said light-emitting element into a plurality of beams, the diffraction grating comprising a non-grating region; and    a focussing member for focussing light that has passed through the diffraction grating;    wherein all or a portion of the light that has passed through the non-grating region enters the focussing member.    
     
     
         12 . An optical device comprising: 
 a light-emitting element for irradiating light onto an information recording medium;    a diffraction grating for splitting light emitted from said light-emitting element into a plurality of beams, the diffraction grating comprising a non-grating region;    a focussing member for focussing the beams that have been split by the diffraction grating onto the information recording medium;    a deflection member for deflecting the plurality of beams after they have been reflected from the information recording medium; and    a photodetector for receiving the plurality of beams after they have been deflected by the deflection member;    wherein all or a portion of the light that has passed through the non-grating region enters the focussing member.    
     
     
         13 . The optical device of  claim 11  or  12 , wherein a diffraction grating depth of the diffraction grating changes stepwise with a constant period.  
     
     
         14 . The optical device of  claim 11  or  12 , wherein the diffraction grating is a blazed grating.  
     
     
         15 . The optical device of  claim 11  or  12 , wherein a diffraction efficiency of the diffracting grating is adjusted so as to maximize the amount of light that enters the focussing member after having passed through a region of the diffraction grating other than the non-grating region.  
     
     
         16 . The optical device of  claim 12 , wherein 
 light that has passed through the non-grating region is used as a main beam for recording/reproducing an information signal on/from the information recording medium;    +1-order and/or −1-order diffraction light in the diffraction grating is used as a sub-beam for detecting a tracking error signal; and    the entire sub-beam passes through a region of the diffraction grating other than the non-grating region.    
     
     
         17 . The optical device of  claim 11  or  12 , wherein 
 the non-grating region is stripe-shaped; and  
 the grating of the diffraction grating is parallel to the non-grating region.  
 
     
     
         18 . The optical device of  claim 11  or  12 , wherein the non-grating region is stripe-shaped; and 
 the grating of the diffraction grating is tilted by a predetermined angle with respect to the non-grating region.  
 
     
     
         19 . The optical device of  claim 2  or  12 , further comprising a circuit for amplifying an electrical signal from the photodetector.  
     
     
         20 . The optical device of  claim 2  or  12 , wherein the deflection member is a diffraction grating functioning as a lens.  
     
     
         21 . The optical device of  claim 2  or  12 , further comprising a polarization beam splitter  
     
     
         22 . The optical device of  claim 2  or  12 , wherein at least the light-emitting element and the photodetector are integrated in the same housing.