| 摘要 |
PURPOSE: To reproduce at least two kinds of optical disks having different track pitches with high accuracy and reliability by simple adjustment. CONSTITUTION: A diffused laser beam transmitted from a light source 11 is diffracted by a diffraction grating 12 and divided into three beams of a zero order,±1st order beams. The respective laser beams diffracted by the diffraction grating 12 are reflected by a beam splitter 13 and introduced to an objective lens 9. The objective lens 9, whose tracking and focusing are controlled by a biaxial mechanism 10, converges the respective laser beams on the information signal layer e.g. a first information signal layer la and a second information signal layer 1b of a double layer optical disk 1 and forms three spots. Three reflected laser beams from the information signal layer 1a or the information signal layer 1b of the double layer optical disk 1 reach the light receiving surface of a photodetector 14 through the objective lens 9 and the beam splitter 13.
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