| 摘要 |
PURPOSE:To stabilize the focus control of the scan light even when a track is crossed by separating the light returned from an optical disk and superposing the 0th order and + or -1st order diffracted beams of separated luminous fluxes on each other. CONSTITUTION:The light radiated from a semiconductor laser 1 is stopped down on a record surface 6 of a optical disk via a beam splitter 3, a 1/4 wavelength plate 4 and a lens 5. The reflected light on the surface 6 goes straight along the splitter 3 and decomposed into two luminous fluxes A and B of the same light quantity via half mirrors 7 and 8. Both fluxes A and B are partly cut by knife edges 9a and 9b with other parts of both fluxes stopped down by an astigmatic lens 10. These stopped-down beams are condensed on a four- split photodetector 11 and therefore a focus error signal is obtained. At the same time, the beams transmitted through both mirrors 7 and 8 are stopped down by a convex lens 12 and condensed on a two-split photodetector 13. Thus, a tracking error signal is obtained. In this case, a part where the 0th order and 1st order diffracted beams of the flux A overlap each other is superposed on a part where the 0th order and -1st order diffracted beams of the flux B overlap each other at both edges 9a and 9b. |
