| 摘要 |
PURPOSE:To obtain a focusing photodetector which has a small photodetecting area and can be attached with high accuracy, by dividing a photodetecting surface into equal four parts with an orthogonal reticle. CONSTITUTION:The optical axis of a condenser lens 20 is set in the Z direction together with axes (y) and (x) set in the vertical and orthogonal directions respectively. The (x) direction of a photodetector 240 is set in parallel with a knife edge 22, i.e., the linear edge of the photodetector 240. Here monitor signals [{A1+(-A1)}-{B1'+(-B1)}] is obtained from the outputs A1', -A1, B1' and -B1 given from elements A', -A, B' and -B respectively. In this case, it is supposed that a focused state is secured. Thus the photodetecting surface of the photodetector 240 is coincident with condensed point of the condensed luminous flux L of the lens 20. Then the photodetector 240 is displaced in the (y) direction to control said monitor signal to 0 and then in the (x) direction to control a monitor signal [{A1+B1}-{(-A1)+(-B1)}] to 0 respectively. Here the spot of the flux L is set accurately at the center of the photodetector 240. Under such conditions, the photodetector 240 is fixed and the width W and the height H of the photodetector 240 are decided by the edge 22 and the lens 20. In such a way, the photodetector 240 can be miniaturized and attached easily.
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