| 摘要 |
PURPOSE:To perform high-precision, stable focus servo and tracking servo by detecting defocusing and a track shift by using individual photodetecting elements without causing any light to strike a defocusing detecting element during focusing. CONSTITUTION:Projection light from a semiconductor laser 1 is passed through a polarization beam splitter 2 ad made into parallel through by a collimator lens 3, the parallel luminous flux illuminates a disk 6 through a quarter-wavelength plate 4 and an objective 5, and its reflected light from the disk 6 is passed through the lens 5 and plate 4 and converted into converged light by the lens 3; and the light is split in direction orthogonal to the incident luminous flux and incident on a beam splitter 7. The reflected luminous flux is split into a direction perpendicular to the optical axis direction and in the optical axis direction through the splitter 7 Concentric two-division photodetecting elements 8 and 8 are arranged at image nonformation points B and B' distant from and close to the splitter at the same distance from conjugate points A and A' at the projection end of the laser 1 in the direction perpen dicular to the optical axis direction and adjusted so that the outer edge of the half luminous flux is aligned to dark lines of the two-division photodetecting elements during focusing. |
