| 摘要 |
<P>PROBLEM TO BE SOLVED: To eliminate disturbance occurring to a defocus signal when an optical spot crosses a track on a recording film surface in accompanying the eccentricity of an optical disk center and to cancel offset of a tracking error signal accompanying lens movement. <P>SOLUTION: A wave front phase of ±one-dimensional diffracted light is shifted by λ/2 in a cycle Dλ/2 (2P*NA) by a phase reverser diffraction grating 701 in which a phase reverses in the same cycle as above in the radial direction of an optical disk and a sub-spot is arranged on the same track as the main spot on the optical disk. By adding a main- and sub-spot defocus error signals in an appropriate gain ratio, the disturbance occurring to the defocus error signal can be canceled. By subtracting the main- and sub-spots tracking error signals by a push/pull system in an appropriate gain ratio, the offset can be canceled. <P>COPYRIGHT: (C)2004,JPO |
