| 摘要 |
PURPOSE:To obtain a compact optical head by using a diffraction grating by dividing the reflected light sent from a recording medium through an image forming lens centering on a boundary line and leads these divided beams to a photodetector. CONSTITUTION:The radiated light 2 of a semiconductor laser 1 passes through a diffracting grating 17 as the diffracted light and focused on a disk surface 13 by an image forming lens 18. This focused light is diffracted by the grating 17 and reaches the 2-split photodetectors 19 and 20 set at the both sides of the laser 1 in the form of the diffracted beams 15 and 16 respectively. The photodetectors 19 and 20 consist of photodetectors 9 and 10 and photodetectors 11 and 12 respectively. The focused points 25 and 26 are set coincident with the dividing line between the photodetectors 9 and 10 and the dividing line between the photodetectors 11 and 12 respectively. Thus it is possible to obtain the focus error signal, the tracking error signal and the reproduction signal.
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