Die processing method, die, objective lens, and optical pick-up device

An objective lens used for an optical pick-up device compatible with different types of optical disks and to focus a light flux onto an information recording surface of each of the optical disks, comprising:

• at least one optical surface including an optical path difference providing structure,
• wherein the objective lens is a plastic lens,
• wherein the optical path difference providing structure includes ring-shaped zones,
• wherein on a cross section of the objective lens in the optical axis direction, a first slope which is closer to the optical axis in the part of ring-shaped zones inclines so as to deviate from the optical axis as the first slope proceeds to the tip of the part of ring-shaped zones and a second slope which is farther from the optical axis in the part of ring-shaped zones is parallel to the optical axis or inclines so as to get close to the optical axis as the second slope proceeds to the tip of the part of ring-shaped zones,
• wherein following formula is satisfied:
• 0°≦θ2′≦15° Formula (7)
• where θ2′ is an acute angle between the optical axis and the second slope.