| 摘要 |
The beam splitter has a diffraction grating (30) formed on its surface. A condenser lens (5) converges the subbeams reflected by the beam splitter on an optical type data storage medium (7) as a no. of spots. A light detector (10) receives the subbeams which are reflected by the medium and are again passed through the lens and the beam splitter. An unfocussed beam spot on the medium is detected by sensing deformation of the zero-order sub-beam on the light detector, while data stores on the medium are repoduced by the zero-order sub- beam. Deviation of a converged beam spot of the zero-order sub-beam from a data track on the medium is detected by the other sub-beams.
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