Holographic multiplex recording method, and holographic recording apparatus and holographic recording medium employing the method

Abstract

A holographic multiplex recording method which can keep a recording data rate constant and equalize nonuniformity in recording due to vibrations or the like, and a holographic recording apparatus and a holographic recording medium, which employ the method are provided. In a process of multiplex-recording information, the time of exposure to a laser beam per data page is kept constant, and the laser output power of the laser beam is increased in accordance with a decrease in recording sensitivity of the holographic recording medium.

1 . A holographic multiplex recording method for multiplex-recording information as a hologram on a holographic recording medium using interference fringes of an object beam and a reference beam, into which a laser beam is split, wherein 
 in a process of multiplex-recording the information, a time of exposure to the laser beam per data page is kept constant, and a laser output power of the laser beam is increased in accordance with a decrease in recording sensitivity of the holographic recording medium.    
   
   
       2 . A holographic multiplex recording method for multiplex-recording information as a hologram on a holographic recording medium using interference fringes of an object beam and a reference beam, into which a laser beam is split, wherein 
 in a process of multiplex-recording the information, a time of exposure to the laser beam per data page and a laser output power are kept constant, and a spatial light modulator having a plurality of pixels for intensity modulating of the object beam is used to increase the number of pixels of the spatial light modulator to be allocated to one bit of the information in accordance with a decrease in recording sensitivity of the holographic recording medium.    
   
   
       3 . The holographic multiplex recording method according to  claim 2 , wherein an array of pixels of the spatial light modulator to be allocated to one bit of the information is formed in a square grid shape.  
   
   
       4 . The holographic multiplex recording method according to  claim 2 , wherein, when a recording sensitivity of the holographic recording medium is reduced to less than or equal to 1/N 2  (N is an integer equal to two or greater) of an initial value of the recording sensitivity, the number of pixels of the spatial light modulator to be allocated to one bit of the information is increased to N 2 .  
   
   
       5 . A holographic recording apparatus for multiplex-recording information as a hologram on a holographic recording medium using interference fringes of an object beam and a reference beam, into which a laser beam is split, wherein 
 in a process of multiplex-recording the information, a time of exposure to the laser beam per data page is kept constant, and a laser output power of the laser beam can be increased in accordance with a decrease in recording sensitivity of the holographic recording medium.    
   
   
       6 . A holographic recording apparatus for multiplex-recording information as a hologram on a holographic recording medium using interference fringes of an object beam and a reference beam, into which a laser beam is split, 
 includes a spatial light modulator having a plurality of pixels for intensity modulating of the object beam, and    wherein    in a process of multiplex-recording the information, a time of exposure to the laser beam per data page and a laser output power are kept constant, and the number of pixels of the spatial light modulator to be allocated to one bit of the information is set to increase in accordance with a decrease in recording sensitivity of the holographic recording medium.    
   
   
       7 . The holographic recording apparatus according to  claim 6 , wherein an array of pixels of the spatial light modulator to be allocated to one bit of the information is formed in a square grid shape.  
   
   
       8 . The holographic recording method according to  claim 6 , wherein the number of pixels of the spatial light modulator to be allocated to one bit of the information is set to increase to N 2  when a recording sensitivity of the holographic recording medium is reduced to less than or equal to 1/N 2  (N is an integer equal to two or greater) of an initial value of the recording sensitivity.  
   
   
       9 . A holographic recording medium on which information is multiplex recorded as a hologram using interference fringes of an object beam and a reference beam, into which a laser beam is split, wherein 
 a time of exposure to the laser beam and a laser output power are kept constant, and a spatial light modulator having a plurality of pixels for intensity modulation of the object beam is used to increase the number of pixels of the spatial light modulator to be allocated to one bit of the information in accordance with a decrease in recording sensitivity of the holographic recording medium, thereby allowing the information to be multiplex-recorded.    
   
   
       10 . The holographic recording medium according to  claim 9 , wherein an array of pixels of the spatial light modulator to be allocated to one bit of the information is formed in a square grid shape, thereby allowing the information to be multiplex-recorded.  
   
   
       11 . The holographic recording medium according to  claim 9 , wherein, when a recording sensitivity of the holographic recording medium is reduced to less than or equal to 1/N 2  (N is an integer equal to two or greater) of an initial value of the recording sensitivity, the number of pixels of the spatial light modulator to be allocated to one bit of the information is increased to N 2 , thereby allowing the information to be multiplex-recorded.  
   
   
       12 . The holographic multiplex recording method according to  claim 3 , wherein, when a recording sensitivity of the holographic recording medium is reduced to less than or equal to 1/N 2  (N is an integer equal to two or greater) of an initial value of the recording sensitivity, the number of pixels of the spatial light modulator to be allocated to one bit of the information is increased to N 2 .  
   
   
       13 . The holographic recording method according to  claim 7 , wherein the number of pixels of the spatial light modulator to be allocated to one bit of the information is set to increase to N 2  when a recording sensitivity of the holographic recording medium is reduced to less than or equal to 1/N 2  (N is an integer equal to two or greater) of an initial value of the recording sensitivity.  
   
   
       14 . The holographic recording medium according to  claim 10 , wherein, when a recording sensitivity of the holographic recording medium is reduced to less than or equal to 1/N 2  (N is an integer equal to two or greater) of an initial value of the recording sensitivity, the number of pixels of the spatial light modulator to be allocated to one bit of the information is increased to N 2 , thereby allowing the information to be multiplex-recorded.