| 摘要 |
PURPOSE:To attain the focus control conveniently and with a high sensitivity by inclining the central line of the focus side interface of a lens located at a focus side to the optical axis of other lens, forming an approximately linear diffracted pattern at a dividing light detecting device and removing a focus signal with the differential output. CONSTITUTION:When the distance of an objective lens and a light disk surface is made near or far, a linear diffracted pattern 30 is moved in the rectangular direction (X direction) to the linear direction of the diffracted pattern 30 at the position of a two-divided photodetector. For example, the diffracting pattern 30 located at the center at the time of focusing, when an objective lens is made far from the optical disk surface, is dislocated in a +X direction, and when the objective lens is made near to the optical disk surface, is dislocated in the reverse -X direction from the center. Further, when the lens is made near to the optical disk, the diffracted pattern itself is composed of one linear shape, deformed, divided into several pieces and the whole is further dislocated in the -X direction. Consequently, by removing the differential output of the two-divided light detecting device, the dislocation from the time of the focusing can be detected. |
