| 摘要 |
PURPOSE:To detect the focus dislocation with, high accuracy and to obtain the satisfactory reproducing signal in SN ratio by separating the photodetecting element of at least two divisions or above having the dividing line in the radius direction and in the parallel direction on respective optical axes at the equal distance only from the image forming point, and arranging one side element at the side near the disk and other side element at the side far from the disk. CONSTITUTION:When the light reflected by a disk 6 is collected by an objective lens 5 and makes incident on a polarizing beam splitter 7, according to the action of a 1/4 wavelength plate and a polarizing beam splitter 7, a reflecting light flux, which passes through a half with the plane formed in the radius direction of an optical axis and the disk 1 as a border, and the reflecting light flux, which passes other half, are mutually divided in the reverse direction. On respective optical axes, at the equal interval away from conjugate points A and A' of the coming out edge of a semiconductor laser 1, at one side, two-division photodetecting elements 8 and 8' having the division line parallel in the radius direction of the disk are arranged at a non-image forming point B far from the polarizing beam splitter, and at other side, they are arranged at anon-image forming point B' near the polarizing beam splitter 7, and respective half light fluxes are made incident, and the two-division photodetecting elements 8 and 8' are adjusted so that the output of respective photodetecting elements may be the same at the time of focusing. |
