| 摘要 |
An objective lens element which has excellent compatibility with optical discs having different base material thicknesses is provided. An objective lens element 141 has optically functional surfaces on an incident side and an exit side. Either one of the optically functional surfaces is divided into an inner part 131B including a rotational symmetry axis and an outer part 131F which is a ring-shaped region surrounding the inner part 131B. On the inner part 131B, a plurality of discontinuous steps are provided. The plurality of steps change in height in the same direction from the optical axis toward the outer part, and each of the steps causes a constant optical path difference longer than the wavelengthλ1 to the first incident light beam 61 and causes a constant optical path difference shorter than the wavelengthλ2 to the second incident light beam 62.
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