| 摘要 |
PURPOSE:To eliminate the need for a shaping prism and to constitute the optical head of a thin optical element so as to make the optical head thin in thickness, small in size, and light in weight by using a reflecting mirror with a cylindrical surface instead of a 45 deg.-plane reflecting mirror which changes the optical axis of parallel rays of light in an orthogonal direction. CONSTITUTION:A reflecting mirror 14 having a cylindrical surface is used instead of a 45 deg.-plane reflecting mirror. When elliptical parallel rays of light are projected on the reflecting mirror 14, the optical axis of the rays of light is changed in the orthogonal direction and the rays of light are projected toward an information recording medium and, at the same time, since the reflecting surface is formed to a cylindrical surface, the rays of light are expanded in the minor-axis direction and the light quantity distribution of the light converged by an objective lens 7 can be made almost uniform between the radial direction and peripheral direction. Therefore, the beam converged by the lens 7 can become a uniform circular beam with a small diameter. Therefore, the reflecting mirror can be used as a shaping prism and 45 deg.-plane reflecting mirror without spoiling the characteristic of the beam. Accordingly, no shaping prism is required and this optical head can be made thinner in thickness, smaller in size, and lighter in weight. |
