OBJECTIVE LENS UNIT, AND OBJECTIVE LRNS ACTUATOR MODULE

摘要

PROBLEM TO BE SOLVED: To provide an objective lens unit capable of suitably correcting spherical aberration caused when light from a light source is condensed on two optical disks having thicknesses different from each other, and to provide an objective lens actuator module.

SOLUTION: The objective lens unit 100 selectively condensing light from a semiconductor laser on a BD 3 and an HD 4 includes: an objective lens 1 having an aspherical shape condensing light from the semiconductor laser on an optical disk having a substrate thickness intermediate between the thicknesses of the BD 3 and the HD 4 in the range of the numerical aperture of the HD 4 and an aspherical shape condensing light from the semiconductor laser on the BD 3 in the range of an outer edge side of the range of the numerical aperture of the HD 4 and the range of the numerical aperture of the BD 3; and a liquid crystal element 2 giving a retardation of nearly (j/k)λ to transmission light in the range of the numerical aperture of the HD 4. The liquid crystal element 2 gives the retardation by changing the code of the retardation when light from the semiconductor laser is condensed on the BD 3 or the HD 4.

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