| 摘要 |
PURPOSE:To obtain an optical pickup, which is light in weight and to which application of any mechanical focus servo is not required, by making the resultant focal length of an optical system variable by means of a Fresnel zone plate using a liquid crystal panel. CONSTITUTION:Laser light 11 emitted from a semiconductor laser 1 is focused on a disk base plate 7 after it is passed through a Fresnel zone plate using a transmission type liquid crystal panel 3 and optical lens 5. When this optical system is applied to the focus servo of the optical pickup, the focusing position is controlled by calculating a new focusing position by means of a CPU 15 in accordance with a detection signal of a focusing position shifting detecting circuit 13 and changing the resultant focal length by changing the spatial frequency of the Fresnel zone plate using the liquid crystal panel 3 by accessing a pattern generator 9. Therefore, an optical system which has no mechanically driven section and whose focal length is variable can be formed. |
