| 摘要 |
PURPOSE:To attain a stable tracking action by detecting the different frequency signals from the reflected light of a laser spot condensed on an optical disk and performing the tracking of the recording/reproduction laser spot so that a fixed ratio is secured for intensity of the frequency signal. CONSTITUTION:The laser light 1 delivered from a light source is condensed on a recording plane 6 of an optical disk 5 through a polarized beam splitter 2, a 1/4 wavelength plate 3 and a condenser lens 4. The plane 6 of the disk 5 includes guide parts 7 and 8 having different reflection factors from the plane 6 and also different cycles formed along both sides of an information recording track. Thus the reflected light sent from the plane 6 are irradiated on a photodetector 9 through the lens 4, the plate 3 and the splitter 2. In a rotation mode of the disk 5 the signal detected by the detector 9 contains two different frequency components according to changes of reflection factors of both parts 7 and 8. Thus the condensed laser spot can be tracked to a fixed position between both parts 7 and 8 by performing the position control of the lens 4 so that the ratio between both frequency components is fixed for the signal detected by the detector 9.
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