| 摘要 |
PURPOSE:To simplify a laser driving circuit by providing a filter positioned so as to be located in an optical path emitted advancing to a disk in an optical head and whose density is changed in the radius direction of the disk independently from the optical head. CONSTITUTION:An ND filter 18 is provided along the moving direction of the optical head 17 piercing through the optical head 17, and the density of the filter 18 is varied in the radius direction of the disk 1 so that high density (low transmission factor) is set at the inner periphery of the disk 1. Therefore, since the density of the filter 18 is increased by moving the optical head 17 in the inner peripheral direction where the linear velocity of the disk 1 is low, laser power arriving at the disk 1 is decreased. By varying the density of the filter 18 appropriately in the radius direction of the disk 1, it is possible to set the optimum power extending over the entire areas of the disk by controlling the laser driving circuit so as to keep the power emitted from the laser, thereby, the laser driving circuit can be simplified. |
