| 摘要 |
PURPOSE: To increase the light efficiency of light beams by removing a beam splitter and providing an improved knife edge. CONSTITUTION: The reflection surface 34 of the knife edge 20 is attached in the form of being tilted at a predetermined angleθ, preferably 45 deg., to an optical axis 60 formed by a convergence point 17 on an optical disk 19 and a photodetector 22. The reflected light beams from the recording surface 18 of the optical disk 19 are converged by an objective lens 16, passed through the knife edge 20, made incident on the light receiving surface 27 of the photodetector 22 and outputted by the form of light intensity measurement by first and second photoelectric cells 32 and 33 formed on the light receiving surface 27. A differential amplifier 28 compares the output of the first and second photoelectric cells 32 and 33 and generates focus error signals. That is, by using the improved knife edge instead of a conventional knife edge without using the beam splitter, the light efficiency of the light beams is increased.
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