| 摘要 |
PURPOSE:To simplify a constitution and to reduce the cost of a focus detector, by using a parallel flat plate or a prism as a means to give astigmatism. CONSTITUTION:For an optical device for information reproducer, the laser light given from a semiconductor laser light source 1 is condensed on a disk 6 through a cemented lens 2, a polarized beam splitter 3, a lambda/4 plate 4 and an objective lens 5. The reflected light goes backward, and the astigmatism is given to the focused light given from a condenser lens 7 by a parallel plane plate 13. Then the reflected light is made incident to a 4-split photodetecting element. Thus the focus detection is carried out. The plate 13 is used in place for a cylindrical lens as a means to give the astigmatism. This simplifies the constitution and reduces the cost of a focus detector. |
