| 摘要 |
PROBLEM TO BE SOLVED: To converge an excellent light spot on an optical disk without aberration even when an optical element such as a half mirror etc. lies between a light source and a light convergent means, to improve a latitude in a shape of an optical head and to facilitate its manufacture by providing a correction means generating the aberration opposite to the aberration caused by the optical element and canceling the aberration. SOLUTION: A light beam 1a from a laser 1 passes through a prescribed path, and is converged on an objective lens 9 to form a light spot on a recording surface on the optical disk 10. At this time, when the light beam 1a transmits through a dichroic mirror 5, a spherical aberration occurs. For correcting this aberration, a cylindrical lens 4 of a parallel plane plate with the same thickness and diffractive index as the dichroic mirror 5 is provided in the optical path of the light beam 1a so that an optical axis coincides with the optical axis of the light beam 1a, and the lens 4 is tilted with the dichroic mirror 5 by 45 deg.. Thus, the aberration is canceled to be made zero. |
