| 摘要 |
PURPOSE:To detect the focus error of the astigmatism system with a simple optical system where astigmatism is caused in a reflected luminous flux and no cylindrical lens used by forming a luminous flux separating face of a beam splitter as a curved face so as to separate the reflected luminous flux from an irradiated luminous flux. CONSTITUTION:The luminous flux separating face 18 of the beam splitter 6 separating the irradiated luminous flux 2 from a light source 1 an the reflected luminous flux from a focused spot on an optical disc 4 is formed as a cylindrical face. Thus, the splitter 6 acts like a parallel flat plate to the luminous flux 2 but uses its split face 18 as a cylindrical mirror to the luminous flux 5, which is separated from the luminous flux 2 and converted into the astigmatism luminous flux at the same time. Thus, the automatic focus adjusting mechanism of the astigmatism system is realized by a simple optical system while not employing a cylindrical lens, the number of components is decreased to simplify the head device. |
