| 摘要 |
PURPOSE:To set a zero cross point in a proper position and to prevent the damage of an information recording medium due to the contact of an objective lens by providing a bent body sandwiched by two plane surfaces between the information recording medium and a photodetector, and permiting two plane surfaces having inclination angles each different to an optical axis, respectively. CONSTITUTION:A light beam from a light source 2 is focused through a polarized beam splitter 4 onto an optical disk 12, the reflected light is reflected on a polarizing surface 6, and it is made incident on a photodetector 16 in being transmitted through a prism optical member 14 to be an optical path length converting means. Since the optical member 14 has two plane surfaces having the inclination angles different to the optical axis, a zero cross signal is generated from a processing circuit 18 to process a signal from the detector 16 at the time of moving in a direction in which an objective 10 is separated from the information recording medium 12. Consequently, even when the objective lens 10 is moved in the direction to approach the information recording medium 12, the contact of the objective 10 with the information recording medium 12 can be prevented, and a focus can be controlled. |
