OPTICAL ELEMENT AND OPTICAL PICKUP DEVICE

摘要

PROBLEM TO BE SOLVED: To provide an optical element that is used for reproducing and/or recording information on at least two types of optical disks, has wavelength selectivity in a diffraction structure, and can improve machining properties and diffraction efficiency, and to provide an optical pickup device thereof.

SOLUTION: The optical element has a diffraction structure in which at least first luminous flux with a wavelength λ1 and second luminous flux with a wavelength λ2 enter. In each diffraction period, depth (d) in the direction of the optical axis of optical surfaces of two adjacent annulars is given by an expression 0.96×m1×λ1/(n1-1)≤d≤1.04×m1×λ1/(n1-1). A diffraction period A is present, where the number of annulars existing in one diffraction period differs according to the diffraction period, and the width vertical to the optical axis of each annular other than the annular for giving the largest optical path length to passing luminous flux is composed of at least two types of different widths.

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