| 摘要 |
PURPOSE:To eliminate the influence of a coma, and to exactly perform a focusing, by almost intersecting orthogonally the directions of a parallel fringe at a center part with a track groove optically, out of S-shaped interference fringes which represent the coma of a lens consisting of a head. CONSTITUTION:The interference fringe of the coma in an objective lens 57 or a collimator lens 52 is monitored. And a constant relation with an axis 13 which represents the direction of the parallel fringe at the center of the S-shaped interference fringe representing a monitored coma, is marked 11 on the lens barrel of the lens 57 or the lens 52. At the assembling time of the lens 57 or 52 in an optical head, the directional characteristic of the coma is recognized by the mark 11. And the rotating alignment of the lenses 57 and 52 around the optical axis is performed so as to intersect orthogonally the axis 13 which represents the directional characteristic of the coma, with a track groove 21. In this way, a semicircular pattern on a four split optical detector is irradiated with uniform light intensity, and the outputs of detecting parts 74a and 74b become ones in proportion exactly to the light receiving area of a semicircular pattern 76, and the focusing of the optical spot with high accuracy can be performed. |
