HOLOGRAM OPTICAL ELEMENT, MISALIGNMENT DETECTING DEVICE, DRIVING DEVICE FOR OPTICAL RECORDING MEDIUM, AND METHOD FOR MANUFACTURING HOLOGRAM OPTICAL ELEMENT

摘要

PROBLEM TO BE SOLVED: To provide a driving device for an optical recording medium equipped with a hologram optical element for controlling the light spot on a light detector to a desired size and for obtaining stable focus error signals and reproducing signals. SOLUTION: In the hologram pattern 40 formed in the hologram optical element, the diffracted beam is twisted by a pattern 1a in the clockwise direction to form a semicircular spot Sa of the converging light on the light detecting parts A, B, crossing the division line LX of a quadripartite light detecting part 60. The diffracted beam is also twisted by a pattern 1b in the clockwise direction to form a semicircular spot Sb of the converging light on the light detecting parts C, D, crossing the division line LX of the quadripartite light detecting part 60.