| 摘要 |
PROBLEM TO BE SOLVED: To provide compatibility and to obtain excellent signal detection regardless of a specification of a disk by dividing an objective lens to a ring-shaped inside area, a round lens area and an outside area and forming a convergent spot with light passing through any two areas according to thickness of a substrate. SOLUTION: The objective lens 20 is divided to the ring-shaped inside area A1 having a prescribed numerical aperture around the vertex V1 of the light source side lens surface 22 of the objective lens 20, the round lens area A2 and the outside area A3. When a thin optical disk 30A is recorded/reproduced at an operational distance WD1, a focal point is formed on an information recording surface 31A by transmission light through the areas A1, A3, and on the other hand, the light transmitting through the round lens area A2 is scattered as shown by a dotted line to prevent a noise disturbance from causing. Further, when a thick optical disk is recorded/reproduced, a spot is formed on the information recording surface by the light transmitting through the inside area A1 and the round lens area A2, and on the other hand, the light transmitting through the outside area A3 is scattered to prevent a noise impediment from occurring. |
