| 摘要 |
PURPOSE:To precisely perform a focus control and accurately detect an information recording signal by removing the offset of a focus signal even when the wavelength of a light source such as a semiconductor laser, etc., fluctuates due to the change of ambient temperature. CONSTITUTION:By making reflection light from a disk 6 incident again on a prism 11 having the same vertical angle as a beam forming prism 3, the light beam going out the prism 11 is made in parallel with the light beam from a semiconductor laser 1 before changing the wavelength and the outgoing light beam is made to incident on a detection lens 7 at the same incident angle. Even when the wavelength of the light source is changed, the light collecting position can be kept at the same position on a focus detection light receiving element and thus, excellent recording, reproducing and erasing characteristics can be obtained. |
