Optical disk apparatus compatible with different types of mediums

Abstract

A polarizing beam splitter for separating an upstream beam from a downstream beam according to the polarization of an incident beam is provided between first and second light sources emitting laser beams at respective wavelength and an objective lens. A phase plate for providing a phase difference to a beam incident on the polarizing beam splitter is provided between the polarizing beam splitter and the light sources. A portion of the laser beam incident on the polarizing beam splitter is reflected by the polarizing beam splitter and caused to be incident on a photo-detecting unit, so as to prevent an unnecessary portion of the laser beam is incident on the photo-detecting unit. According to the invention, the laser beam is used efficiently and the cost of fabricating an optical disk apparatus is reduced by eliminating a need for a gain controlling circuit in the photo-detecting unit.

What is claimed is:  
     
         1 . An optical disk apparatus comprising: 
 two information recording mediums having different base thickness;    two laser beam sources emitting respective laser beams of different wavelength commensurate with respective base thickness;    an objective lens for converging the laser beams from said two laser beam sources so as to form respective beam spots on said two information recording mediums;    polarizing optical path separating means which, provided between said two laser beam sources and said objective lens, separates an optical path for an upstream laser beam from an optical for a downstream laser beam depending on polarization of laser beams incident on said polarizing optical path separating means;    a first phase plate which, provided between said two laser beam sources and said polarizing optical path separating means, provides a predetermined phase difference to laser beams incident from said two laser beam sources incident on said polarizing optical path separating means; and    photosensitive means for receiving the downstream laser beam exiting said polarizing optical path separating means.    
     
     
         2 . The optical disk apparatus as claimed in    claim 1   , further comprising: 
 a second phase plate which, provided between said polarizing optical path separating means and said objective lens, provides a phase difference of approximately ¼ of a wavelength between incident laser beams transmitted through said second phase plate from said two laser beams sources.    
     
     
         3 . The optical disk apparatus as claimed in    claim 1   , wherein at least one of said first phase plate and said second phase plate is formed to be integral with said polarizing optical path separating means.  
     
     
         4 . The optical disk apparatus as claimed in    claim 1   , wherein at least one of said phase plate and said second phase plate is embodied by a vapor-deposited film.  
     
     
         5 . The optical disk apparatus as claimed in    claim 1   , wherein said polarizing optical path separating means is embodied by a polarizing diffraction grating for one of diffracting and transmitting an incident laser beam depending on polarization of the incident laser beam.  
     
     
         6 . The optical disk apparatus as claimed in    claim 1   , wherein said photosensitive means comprises two photosensitive elements for receiving a downstream laser beam exiting said polarizing optical path separating means, said optical further disk apparatus further comprising laser beam splitting means for splitting laser beams from said polarizing optical path separating means so as to direct each of the split laser beams to a respective one of said two photosensitive elements depending on a wavelength of the split laser beam.  
     
     
         7 . The optical disk apparatus as claimed in    claim 6   , wherein said laser beam splitting means is embodied by a diffraction grating for diffracting an incident laser beams.  
     
     
         8 . The optical disk apparatus as claimed in    claim 6   , further comprising a third phase plate which, provided between said polarizing optical path separating means and said laser beam splitting means, to provide a phase difference which is an integral multiple of the wavelength to an incident laser beam of a first wavelength, and to provide a phase difference which is ½ of the wavelength to an incident laser beam of a second wavelength.  
     
     
         9 . The optical disk apparatus as claimed in    claim 8   , wherein said third phase plate is embodied by a vapor-deposited film.  
     
     
         10 . The optical disk apparatus as claimed in    claim 8   , wherein said third phase plate is formed to be integral with said laser beam splitting means.  
     
     
         11 . The optical disk apparatus as claimed in    claim 8   , wherein said laser beam splitting means is embodied by a polarizing diffraction grating for one of diffracting and transmitting an incident laser beam depending on polarization thereof.  
     
     
         12 . The optical disk apparatus as claimed in    claim 1   , wherein said two laser beam sources and said photosensitive means are accommodated in a laser unit.  
     
     
         13 . The optical disk apparatus as claimed in    claim 12   , wherein said two laser beam sources are semiconductor lasers constructed such that active layers thereof are oriented in directions at right angles to each other.  
     
     
         14 . The optical disk apparatus as claimed in    claim 12   , wherein said first phase plate provides a phase difference which is an integral multiple of the wavelength to a first laser beam from one of said two laser beam sources, and provide a phase difference which is ½ of the wavelength to a second laser beam from the other of said two laser beam sources.  
     
     
         15 . The optical disk apparatus as claimed in    claim 12   , wherein said laser unit includes said first phase plate, said polarizing optical path separating means and said second phase plate.  
     
     
         16 . An optical pickup apparatus compatible with a first optical recording medium adapted for a first wavelength for writing and reading and a second optical recording medium adapted for a second wavelength for writing and reading, comprising: 
 a first light source emitting a first beam at the first wavelength;    a second light source emitting a second beam at the second wavelength;    a coupling lens for coupling one of the first beam and the second beam;    an objective lens for converging the coupled beam so as to form a beam spot on a recording surface of one of the first optical recording medium and the second optical recording medium;    optical path separating means for separating a return beam reflected by the optical recording medium and transmitted through the objective lens, from an upstream optical path leading from the light source to the objective lens, said optical path separating means being provided in alignment with both an upstream beam traveling to the recording surface and the return beam;    detecting means for receiving the return beam separated by said optical path separating means so as to retrieve information from the return beam, said detecting means being provided in alignment with both the upstream beam and the return beam and including photosensitive means;    control means for effecting focusing control and tracking control based on a result of detection by said detecting means, wherein 
 said first light source is driven only when the first optical recording medium is used, the second light source is driven only when the second optical recording medium is used,  
 said coupling lens is embodied by an anamorphic lens which provides different actions in a direction in which a full-width-half-maximum (FWHM) of an angle of divergence with respect to intensity of the beam from the light source is maximum and in a direction in which the full-width-half maximum (FWHM) of the angle divergence is minimum, and which is provided with a collimating function for collimating one of the first beam and the second beam and a beam shaping function for shaping one of the first beam and the second beam.  
   
     
     
         17 . The optical pickup apparatus as claimed in    claim 16   , further comprising: 
 optical axis aligning means for aligning optical axes of the first beam and the second beam with an optical axis of said coupling lens.    
     
     
         18 . The optical pickup apparatus as claimed in    claim 17   , wherein said optical axis aligning means is embodied by a prism element having one of a variable transmissivity and a variable reflectivity that depends on a polarization of an incident beam.  
     
     
         19 . The optical pickup apparatus as claimed in    claim 17   , wherein said optical axis aligning means is embodied by a combination of a prism element having one of a variable transmissivity and a variable reflectivity that depends on a polarization of an incident beam, and a phase plate for rotating a plane of polarization of one of the first beam and the second beam by 90°.  
     
     
         20 . The optical pickup apparatus as claimed in    claim 17   , wherein said optical axis aligning means is embodied by a prism element having a one of variable transmissivity and a variable reflectivity that depends on a wavelength of the beam.  
     
     
         21 . The optical pickup apparatus as claimed in    claim 17   , wherein said optical axis aligning means is embodied by a prism element having a polarization filter characteristic that depends on a wavelength of the beam.  
     
     
         22 . The optical pickup apparatus as claimed in    claim 17   , wherein said optical axis aligning means is embodied by a prism element provided with a first film having one of a variable transmissivity and a variable reflectivity that depends on a polarization of the beam, and a second film having a polarization filter characteristic that depends on a wavelength of the beam, wherein said optical pickup apparatus further comprises: 
 a phase plate for operating as a ¼ wave plate for the first beam and the second beam;    said prism element and said phase plate constitute the optical path separating means by controlling the return beam to be incident on said photosensitive means of said detecting means via said coupling lens, said phase plate and said prism element, and    said photosensitive means and said coupling lens constitute said detecting means.    
     
     
         23 . The optical pickup apparatus as claimed in    claim 16   , the first and second light sources are accommodated in the same package.  
     
     
         24 . The optical pickup apparatus as claimed in    claim 16   , wherein said optical path separating means includes a polarizing hologram.  
     
     
         25 . The optical pickup apparatus as claimed in    claim 24   , wherein said optical path separating means is formed of the polarizing hologram and a phase plate integral with each other, said phase plate operating as a ¼ wave plate for the first beam and for the second beam.  
     
     
         26 . The optical pickup apparatus as claimed in    claim 24   , wherein said optical path separating means is formed of the polarizing hologram provided with phase plates formed on respective surfaces thereof, one of the phase plates rotating a plane of polarization of one of the first beam and the second beam by 90° and the other phase plate operating as a ¼ wave plate for the first beam and for the second beam.  
     
     
         27 . The optical pickup apparatus as claimed in    claim 19   , wherein said phase plate is formed as a vapor-deposited film.  
     
     
         28 . The optical pickup apparatus as claimed in    claim 22   , wherein said phase plate is formed as a vapor-deposited film.  
     
     
         29 . The optical pickup apparatus as claimed in    claim 25   , wherein said phase plate is formed as a vapor-deposited film.  
     
     
         30 . The optical pickup apparatus as claimed in    claim 26   , wherein said phase plate is formed as a vapor-deposited firm.  
     
     
         31 . The optical pickup apparatus as claimed in    claim 23   , wherein said detecting means is accommodated in the same package as said first and second light sources.  
     
     
         32 . The optical pickup apparatus as claimed in    claim 24   , wherein said detecting means is accommodated in the same package as said first and second light sources.  
     
     
         33 . The optical pickup apparatus as claimed in    claim 32   , wherein said optical path separating means including the polarizing hologram is accommodated in the same package as said detecting means and said first and second light sources.  
     
     
         34 . The optical pickup apparatus as claimed in    claim 16   , wherein said first light source emits a beam at a wavelength of 785 nm, said second light source emits a beam a wavelength of 650 nm, said first optical recording medium is a low-capacity optical disk having a base thickness of 1.2 mm and said second optical recording medium is a high-capacity optical disk having a base thickness of 0.6 mm.  
     
     
         35 . The optical pickup apparatus as claimed in    claim 16   , wherein one of said first light source and said second light source provides a TE-mode emission and the other light source provides a TM-mode emission.  
     
     
         36 . An optical pickup apparatus compatible with a first optical recording medium adapted for a first wavelength for writing and reading and a second optical recording medium adapted for a second wavelength for writing and reading, comprising: 
 a first light source emitting a first beam at the first wavelength;    a second light source emitting a second beam at the second wavelength;    a coupling lens for coupling one of the first beam and the second beam;    an objective lens for converging the coupled beam so as to form a beam spot on a recording surface of one of the first optical recording medium and the second optical recording medium;    optical path separating means for separating an optical path of a return beam reflected by the optical recording medium and transmitted through the objective lens, from an upstream optical path leading from the light source to the objective lens, the optical path separating means being provided in alignment with both an upstream beam traveling to the recording surface and the return beam;    detecting means for receiving the return beam separated by the optical path separating means so as to retrieve information from the return beam, the detecting means being provided in alignment with both the upstream beam and the return beam and including photosensitive means;    control means for effecting focusing control and tracking control based on a result of detection by the detecting means,    a beam shaping hologram element for transforming an elliptical intensity profile of the first beam and the second beam into a circular profile, 
 wherein the first light source is driven only when the first optical recording medium is used, the second light source is driven only when the second optical recording medium is used.  
   
     
     
         37 . The optical pickup apparatus as claimed in    claim 36   , wherein said beam shaping hologram element is embodied by a polarizing hologram.  
     
     
         38 . The optical pickup apparatus as claimed in    claim 36   , further comprising a phase plate for providing a predetermined phase difference to the first beam and the second beam.  
     
     
         39 . The optical pickup apparatus as claimed in    claim 38   , wherein said beam shaping hologram element is embodied by a polarizing hologram which is formed to be integral with said phase plate.  
     
     
         40 . The optical pickup apparatus as claimed in    claim 38   , wherein said phase plate provides a phase difference equal to half an integral multiple of the first wavelength and provides a phase difference equal to an integral multiple of the second wavelength.  
     
     
         41 . The optical pickup apparatus as claimed in    claim 36   , wherein said optical path separating means is embodied by an optical path separating hologram element.  
     
     
         42 . The optical pickup apparatus as claimed in    claim 41   , wherein said optical path separating hologram is a polarizing hologram.  
     
     
         43 . The optical pickup apparatus as claimed in    claim 42   , further comprising a plurality of phase plates each providing a predetermined phase difference to an incident beam.  
     
     
         44 . The optical pickup apparatus as claimed in    claim 43   , wherein said beam shaping hologram element and said optical path separating hologram element are both polarizing holograms, and wherein said plurality of phase plates are formed to be integral with said polarizing holograms.  
     
     
         45 . The optical pickup apparatus as claimed in    claim 38   , wherein said phase plate is embodied by a vapor-deposited phase difference film.  
     
     
         46 . The optical pickup apparatus as claimed in    claim 43   , wherein said plurality of phase plates are embodied by vapor-deposited phase difference films.  
     
     
         47 . The optical pickup apparatus as claimed in    claim 36   , where in said first and second light sources are accommodated in a package.  
     
     
         48 . The optical pickup apparatus as claimed in    claim 47   , wherein a photosensitive portion of the said detecting means is provided in the can in which said first and second light sources are accommodated.  
     
     
         49 . The optical pickup apparatus as claimed in    claim 36   , wherein said coupling lens collimates one of the first beam and the second beam, and wherein said beam shaping hologram element is disposed at a location where the first beam and the second beam are parallel beams.  
     
     
         50 . The optical pickup apparatus as claimed in    claim 36   , wherein said beam shaping hologram element is disposed at an optical path leading from said first and second light sources to said coupling lens.  
     
     
         51 . The optical pickup apparatus as claimed in    claim 50   , wherein said first and second light sources are accommodated in a can, and wherein said beam shaping hologram element is formed to be integral with the can.  
     
     
         52 . The optical pickup apparatus as claimed in    claim 36   , further comprising an optical axis aligning means for aligning optical axes of the first beam and the second beam with an optical axis of said coupling lens such that far field patterns of the first beam and the second beam have the same orientation.  
     
     
         53 . The optical pickup apparatus as claimed in    claim 52   , wherein said first and second light sources are accommodated in a can, and said optical axis aligning means is provided in the can.