| 摘要 |
PURPOSE:To perform good focus control irrespective of occurrence of tracking deviation by removing deviation of distribution of intensity of light due to tracking deviation from a beam modulated by an optical recording medium. CONSTITUTION:Faces 45-47 of a prism 42 are parallel to the direction of a track 51 formed on an optical recording medium 25 and arranged to incline to the direction perpendicular to the track 51. In this prism 42, the reflectance of a face 45 which is an interface of prisms 43 and 44 is 1/3 and reflectance of faces 46, 47 corresponding to legs of trapezoidal section of the prism 44 is 1 respectively. In this case, deviation of distribution of intensity of light due to tracking deviation is removed from parallel beam 17 reflected by the prism 42, and push-pull signals are canceled in the parallel beam 17. Accordingly, by using the beam for focus error detection, good focus control can be made irrespective of presence of tracking deviation. |
