| 摘要 |
PURPOSE:To prevent a pseudo signal from being generated and to improve accuracy by unifying the micro displacement of a beam on a quadruple optical detector according to the movement of an objective lens with the direction of the parting line of the detector in one. CONSTITUTION:A beam of light emitted from a light source 1 is reflected on a half mirror 2, and is converged by the objective lens 3, and is image-formed on an optical disk 4. The beam of light reflected on the disk 4 is made incident on the lens 3 again, and is made incident on the quadruple optical detector 5 passing the mirror 2. When an angle made by an axis (u) in the incident direction of the light source 1 and an astigmatic direction and an axis (x) that is the moving direction of the lend 3 is set at 45 deg. -theta, the beam on the detector is displaced in micro distance according to the movement of the lens 3, and is moved on an axis (t') which makes an angle 45 deg. +theta with the axis (u). Therefore, by setting the direction of the parting line of the detector 5 at the one made by the axis (t') and an axis (s') intersecting orthogonally to the axis (t'), no out-of-focus is generated even when the lens 3 is displaced on the axis (x), thereby, the accuracy can be improved. |
