Optical head and method for monitoring light source output in optical head

Abstract

An optical head is composed of a light source means ( 1 ) for generating a luminous flux (A), a polarization beam splitter ( 2 ), an object lens ( 11 ) opposed to an appropriate recording medium ( 12 ), and a power monitoring means ( 6 ) for monitoring the power of the luminous flux (A) output from the light source means ( 1 ). The power monitoring means ( 6 ) is adapted to utilize a luminous flux (B) other than a luminous flux (C) of the luminous flux (A) (the whole amount of light) in order to monitor the power of the luminous flux (A) output from the light source means ( 1 ). The luminous flux (C) is substantially used for reproducing predetermined information from the recording medium ( 12 ) or recording the predetermined information onto the recording medium ( 12 ).

What is claimed is:  
     
         1 . An optical head comprising: 
 a light source means for generating a light beam;    an object lens opposed to a recording medium; and    a power monitoring means for monitoring the power of said light beam emitted from said light source means;    wherein said power monitoring means is adapted to monitor said power of said light beam emitted from said light source means by utilizing a portion of said light beam other than a portion thereof substantially used for reproducing or recording predetermined information from or onto said recording medium.    
     
     
         2 . An optical head as claimed in  claim 1 , wherein said light source means is a semiconductor laser.  
     
     
         3 . An optical head as claimed in  claim 1 , wherein said light beam portion used for monitoring said power of said light beam is a light beam portion constituting a peripheral portion of said light beam.  
     
     
         4 . An optical head as claimed in  claim 1 , wherein said power monitoring means is provided such that it is opposed to said light source means via said polarization beam splitter.  
     
     
         5 . An optical head as claimed in  claim 4 , wherein a half-wave plate having an aperture, which allows only said light beam portion substantially used for reproducing or recording predetermined information to be transmitted therethrough, is applied to a surface of said polarization beam splitter, said surface being opposed to said light source means.  
     
     
         6 . An optical head as claimed in  claim 5 , wherein: 
 said power monitoring means has a photodetecting assembly divided into segments; and    said photodetecting assembly receives an annular light beam transmitted through said half-wave plate and outputs information regarding the output power of said light source means on the basis of the amount of the received annular light beam.    
     
     
         7 . An optical head as claimed in  claim 1 , wherein: 
 a shielding plate having an aperture, which allows only said light beam portion substantially used for reproducing or recording predetermined information to be transmitted therethrough, is applied to a surface of said polarization beam splitter, said surface being opposed to said light source means; and    a plurality of photodetecting elements are disposed along the periphery of said aperture of said shielding plate.    
     
     
         8 . An optical head as claimed in  claim 1 , wherein: 
 a shielding plate having an aperture, which allows only said light beam portion substantially used for reproducing or recording predetermined information to be transmitted therethrough, is applied to a surface of said polarization beam splitter, said surface being opposed to said light source means;    a hologram, which reflects a part of said light beam in a particular direction, is provided along the periphery of said aperture of said shielding plate; and    said power monitoring means is provided in a position toward which said light beam is reflected by said hologram.    
     
     
         9 . An optical head as claimed in  claim 1 , wherein: 
 a reflector having an aperture, which allows only said light beam portion substantially used for reproducing or recording predetermined information to be transmitted therethrough, is abutted against a surface of said polarization beam splitter at a predetermined angle with respect to a surface of said polarization beam splitter, said surface being opposed to said light source means; and    said power monitoring means is provided in a position toward which said light beam is reflected by said reflector.    
     
     
         10 . A method for monitoring a light source output in an optical head, wherein: 
 said optical head comprises a light source means for generating a light beam, a polarization beam splitter, an object lens opposed to a recording medium, and power monitoring means for monitoring the power of said light beam emitted from said light source means; and    said power monitoring means monitors said power of said light beam output from said light source means by utilizing a portion of said light beam other than a portion thereof substantially used for reproducing or recording predetermined information from or onto said recording medium.    
     
     
         11 . A method for monitoring a light source output in an optical head as claimed in  claim 10 , wherein said light source means is a semiconductor laser.  
     
     
         12 . A method for monitoring a light source output in an optical head as claimed in  claim 10 , wherein said light beam portion used for monitoring said power of said light beam is a light beam portion constituting a peripheral portion of said light beam.