Optical scanning device

Abstract

In an optical scanning device for scanning an optical record carrier ( 20 ) and comprising a radiation source ( 2 ), a beam splitter ( 8 ) arranged to pass a first portion (b 3 ) of the source beam (b 1 ) to the record carrier and a second portion (b 5 ) to an intensity sensor ( 10 ), and a signal detector ( 24 ) in the path of the beam reflected by the record carrier, false radiation (b 6 ) reflected by the signal detector can be prevented from reaching the intensity sensor by tilting the signal detector. A polarization filter ( 40 ) may be arranged in front of the intensity sensor to prevent false radiation reflected by the radiation source and by the signal detector from reaching the intensity sensor.

1 . An optical scanning device for scanning an optical record carrier, said device comprising a radiation source for emitting an incident radiation beam, a beam splitter located in the path of the incident radiation beam from the radiation source to the location of said optical record carrier and arranged to pass a first portion of the incident beam intensity, which is incident upon the beam splitter, towards the optical record carrier and to pass a second portion of said incident beam intensity towards an intensity sensor for sensing radiation of the incident beam, and a radiation-sensitive signal detector for converting a radiation beam reflected from said optical record carrier and passing along a path including the beam splitter into electrical detector signals, the device comprising an optical axis extending from the emitting opening of the radiation source via the beam splitter towards the location of the record carrier and back from the record carrier towards the radiation-sensitive detector, characterized by means for preventing reflected radiation reflected from the signal detector and/or the radiation source from reaching the point of intersection of the optical axis and the plane of the intensity sensor.  
     
     
         2 . An optical scanning device as claimed in  claim 1 , characterized in that said means comprises tilting of the signal detector with respect to the local optical axis.  
     
     
         3 . An optical scanning device as claimed in  claim 1 , characterized in that said means comprises a wedge shaped element arranged in the path through the beam splitter up to the signal detector.  
     
     
         4 . An optical scanning apparatus as claimed in  claim 3 , comprising a focus servo lens arranged between the beam splitter and the signal detector, characterized in that the wedge shaped element and the focus servo lens are integrated into one element.  
     
     
         5 . An optical scanning system as claimed in  claim 2 , characterized in that the wedge shaped element is integrated with the beam splitter.  
     
     
         6 . An optical scanning apparatus as claimed in  claim 1 , characterized in that said means comprises a polarization filter arranged between the beam splitter and the intensity sensor and in that a quarter wavelength plate is arranged between the beam splitter and the location of the optical record carrier.  
     
     
         7 . An optical scanning device as claimed in  claim 1 , characterized by the additional measure of arranging the intensity sensor off-axis with respect to the local optical axis.  
     
     
         8 . An optical scanning device as claimed in  claim 1 , characterized in that the beam splitter is a polarizing beam splitter.  
     
     
         9 . An optical scanning device as claimed in  claim 1 , characterized in that the beam splitter is a partially polarizing beam splitter arranged to pass a first proportion of the incident beam intensity which is incident upon the beam splitter and has a first polarization towards the optical record carrier and to pass a second proportion of the reflected beam intensity incident upon the beam splitter and having a second polarization, orthogonal to the first polarization, towards the signal detector, said first proportion of intensity being greater, as a proportion, than said second proportion of intensity.  
     
     
         10 . An optical scanning device as claimed in  claim 9 , characterized in that said beam splitter is arranged to reflect the incident beam and to transmit the reflected beam, the reflectivity of the beam splitter for the polarization of the incident beam being greater than the transmitivity of the beam splitter for the polarization of the reflected beam.  
     
     
         11 . An optical scanning device as claimed in  claim 9 , characterized in that said beam splitter is arranged to transmit the incident beam and to reflect the reflected beam, the transmitivity of the beam splitter for the polarization of the incident beam being greater than the reflectivity of the beam splitter for the polarization of the reflected beam.  
     
     
         12 . An optical scanning device as claimed in  claim 9 , characterized in that said first proportion is greater than 75%.  
     
     
         13 . An optical scanning device as claimed in  claim 9 , characterized in that said first proportion is less than 97%.  
     
     
         14 . An optical scanning device as claimed in  claim 12 , characterized in that said first proportion is between 85% and 95%.  
     
     
         15 . An optical scanning device as claimed in  claim 14 , characterized in that said second proportion is within the range 15% to 75%.  
     
     
         16 . An optical scanning device as claimed in  claim 15 , characterized in that said second proportion is within the range 25% to 62%.  
     
     
         17 . An optical scanning device as claimed in  claim 16 , characterized in that it comprises a second radiation source for emitting a second radiation beam comprising a different predetermined wavelength, and a second beam splitter for reflecting or transmitting said second radiation beam towards the optical record carrier.  
     
     
         18 . An optical scanning device as claimed in  claim 17 , characterized in that the first beam splitter is arranged to have substantially non-polarizing effect on radiation of said second wavelength.  
     
     
         19 . An optical scanning device as claimed in  claim 17 , characterized in that said second beam splitter is arranged to have a substantially non-polarizing effect on radiation of said first and/or said second wavelength.  
     
     
         20 . An optical scanning device as claimed in  claim 17 , characterized in that said second beam splitter is arranged to show approximately 50% transmission for radiation of said second wavelength.  
     
     
         21 . An optical scanning device as claimed in  claim 17 , characterized in that said second beam splitter is arranged to show substantially 100% transmission or reflection for radiation of said first wavelength.  
     
     
         22 . An optical scanning apparatus as claimed in  claim 21 , characterized in that the first and second radiation beam both have writing power and in that the intensity of both beams is measured by an intensity sensor.