| 摘要 |
PURPOSE: To increase the light efficiency of converged light beams reflected from the recording surface of an optical disk by providing a back surface functioning as a reflector on a knife edge and using an improved knife edge method. CONSTITUTION: The light beams sent through a beam splitter 14 are divided into two parts 21 and 23 by the knife edge 20. The back surface 34 functioning as the reflector is attached to the knife edge 20, one part 23 in the converged light beams is reflected from the back surface 34 and made incident on the second detector 37 of a photodetection unit 50 and the converged light 21 of the remaining part is passed through the knife edge 20 and made incident on a first detector 31. Also, the knife edge 20 is inclined at a predetermined angleθ, preferably 45 deg., and attached to a first optical axis 57 vertical to the second detector 37. First and second adders 60 and 62 add output signals from the detectors 31 and 37, the added result is compared by a differential amplifier 28 and focus error signals are generated and outputted.
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