Objective Lens, Optical Pickup Device, and Optical Disk Drive

An objective lens for use in an optical pickup apparatus,

• for forming a converged spot on an information recording surface of a first optical disc including a protective layer with a thickness t1 by using a first light flux with a wavelength λ1 (μm) emitted from a first light source, and
• for forming a converged spot on an information recording surface of a third optical disc including a protective layer with a thickness t3 (t1<t3) by using a third light flux with a wavelength λ3 (1.7λ1<λ3<2.3λ1) emitted from a third light source,
• wherein an optical surface of the objective lens comprises a first basic structure being an optical path difference providing structure,
• the first basic structure comprises a step structure in which a plurality of ring-shaped step units are arranged concentrically about an optical axis as a center, and
• a step-difference amount d1 of a small step difference in each of the step units, in a direction of the optical axis satisfies the following conditional expression, where n is a refractive index of the objective lens for the first light flux:
• 0.5λ1/(n−1)<d1<λ1(n−1) (1)