| 摘要 |
PURPOSE:To simplify a constitution and to realize a light, small-sized, highly precise pick-up by using an optical device with transmissive sections and absorptive sections skewed from an optical axis and controlling a focus. CONSTITUTION:The reflected light of a disc 15 is separated from an incident light in a beam printer 13 and a projected to a photodetecting element 17 through an optical device 16. The optical device 16 consists of absorptive sections 16a and transmissive sections 16b, which are alternately arranged with the absorptive sections 16a skewed from the optical axis by a prescribed angle phi. When the disc 15 is positioned at the focus of an object lens 14, and when the device 16 is so adjusted that parallel light to are made incident thereon, the device 10 receives a diffused light as the disc 15 approaches the lens 14 and a convergent light as the disc 15 goes away from the lens 14; thus the focus is controlled easily. |
