| 摘要 |
PURPOSE:To miniaturize an optical head by dividing the reflected light received from a recording medium through an image forming lens centering on a boundary line, and providing the grid lenses on 1st dividing lines set at both sides of the 2nd dividing line of a photodetector. CONSTITUTION:The light diffracted by an upper grid lens 27 is focused at a point 29 and reaches the dividing line 31 between photodetectors 21 and 22 in the form of the semicircular radiated light. While the light diffracted by a lower grid lens 28 is focused at a point 30 and reaches a dividing line 31 between photodetectors 23 and 24 in the form of a semicircular spot. The spot diameters of both diffracted beams are equal to each other on a 4-split photodetector 25 when the light 14 focused onto a disk surface 13 is set under a focused state. At the same time, the same incident light intensity is secured among those photodetectors 21-24. In such a constitution, only an image forming lens and both grid lenses are needed as optical parts. Therefore, the number of parts can be considerably reduced, which also reduces the size of an optical head device. |
