| 摘要 |
PURPOSE:To reduce a track dislocation detecting error by making the optical axis of a main beam and a sub beam coaxial optical axis in a movable optical system and even between the movable optical system and an optical disk. CONSTITUTION:A main beam 1 and a sub beam 2 of wave lengths lambda2 and lambda2 transmited from a laser light source 15 are horizontal and P polarized lights. lambda2 lambda2 is selected and through a dichroic mirror 4 and lambda/4 plate 5, the beam 2 is brought near to a circularly polarized light. When the light spot diameter of the beam 1 is made almost equal to the channel pitch of a disk 101 by a lens 103 of a movable optical system 8, the dislocation can be detected as a non-balanced quantity of light due to the diffraction of a beam 21. For the optical spot of the sub beam 2, the diffraction is not generated in a reflected beam due to the chromatic aberration of the lens 103. The reflected beam returns to a static optical system 9 and the beam 2 is reflected by the mirror 4 and enters through a glass plate 41 into a detector 10. The plate 41 is turned around a Y-axis as a rotary axis P by the output of the detector 10, the beams 21 and 22 are simultaneously moved to an X direction. The dislocation on both optical axes is corrected and the main beam 21 is made incident on a main beam dislocation detecting means. Thus, the error of the dislocation detecting of a track is reduced.
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