| 摘要 |
PURPOSE:To obtain a compact optical head by providing a grid lens in the direction orthogonal to the information track direction of a recording medium to lead a pair of opposite beams to the 2nd and 3rd photodetecting surfaces. CONSTITUTION:The radiated light 2 of a semiconductor laser 1 passes through a grid lens 17 as the 0-degree diffracted light and is focused on a disk surface 13 via an image forming lens 18. The reflected light received from the surface 13 is focused by the lens 18 and diffracted by the lens 17 to reach a 6-split photodetector 23 set at the side of the laser 1 in the form of four diffracted beams 19-22. When the light 14 focused to the surface 13 is set under a focused state, the spot diameters are equal to each other among those diffracted beams on the photodetectors 24-27 together with the same intensity secured among those incident beams onto the photodetectors 24-27. For this purpose, those detectors 24-27 are properly distributed. Thus a focus error signal is obtained and therefore only the lenses 17 and 18 are needed as the optical parts. In such a way, the number of parts of an optical head device can be extremely reduced. |
