| 摘要 |
PURPOSE:To attain miniaturization by providing a diffraction grating which bisects reflected light from a recording medium through an image forming lens with a boundary line, and leads it to a photodetector. CONSTITUTION:The titled device is so constructed to have a light source 1, the image forming lens 18 stopping the image of the light source 1 on the recording medium, plural photodetectors 19 and 20 which are arranged on both sides of the light source 1 and bisected independently, and the diffraction grating 17, which has different grating pitches with the boundary line intersecting with the optical axis of the image forming lens 18 installed between the light source 1 and the image forming lens 18 as a reference, bisects the reflected light from a recording medium 13 through the image forming lens 18 with the boundary line and leads it to the photodetectors 19 and 20. In terms of the diffraction grating 17, the + or - primary diffraction light of a diffraction grating at right 21 converges at points 23 and 26 on the plane the same as the bisecting photodetector 20. Thus the overall optical disk device is scaled down, and the size of the optical head can be reduced. |
