| 摘要 |
PURPOSE:To form a fine spot on a magneto-optical disk by a compact optical pickup by using an objective lens having the high numerical aperture and a long focal length, and a beam expander to expand the diameter of a laser beam. CONSTITUTION:The beam emitted from a semiconductor laser 1 becomes parallel light flux by a collimator lens 2 and the shape of the beam is corrected to complete round by a cylindrical lens 3. Then, the beam is rectangularly reflected to left by a beam splitter 4 and rectangularly deflected upward by a full reflection prism 5. Afterwards, the beam is made incident to an objective lens 7 having high numerical aperture and the long focal length, while expanding the beam diameter by beam expanders 61 and 62, which are composed of two optical axis symmetric lens systems so as to expand the beam diameter, and the fine spot is formed on a magneto-optical disk 9. Thus, since the light flux to be made incident to the lens 7 is expanded once and converged at the lens 7, the fine spot can be effectively formed at a suitable interval to the disk 9 without losing the light flux. |
