| 摘要 |
PURPOSE:To share optical elements and to simplify an optical system by deflecting the proceeding direction of the reflecting light passing through a beam shaping functional element by means of a deflecting element and guiding the light to a photodetector. CONSTITUTION:A light source 1 is a laser light source and projects anisotropic beams of light. The light beams are turned to a parallel luminous flux by a collimating lens 2, and further shaped to be isotropic by a beam shaping prism 3. Then, the luminous flux is raised by a mirror 4 and guided to an objective lens 5. The luminous flux is condensed by the lens 5, converged and cast onto a recording surface of an optical disc 13, thereby forming fine beam spots. The light reflected at the recording surface of the disc 13 is sent through lenses 5, 2 in the opposite direction to that when the light is guided to the lens 5, and subsequently diffracted and deflected by a holographic element 6 as a deflecting element. The light is eventually detected by photodetectors 7, 8. The output signal is operated at an operational circuit 10 to generate an error signal. Accordingly, a current of a focus driving coil 12 is controlled, thereby controlling the focal position of the beam spots. In this manner, optical elements are used in common and the optical system is simplified. |
