OBJECTIVE LENS AND OPTICAL PICK-UP DEVICE

摘要

Provided are an optical pick-up device and an objective lens which can appropriately record and/or play back the information on three types of disks having different recording densities and improve the light usage efficiency using a simple structure. A first optical path difference imparting structure is formed on the optical surface of the objective lens. The first optical path difference imparting structure has a stepped structure in which disk band-shaped step units having the same number of steps are arranged in a plurality of concentric shapes with the optical axis as the center. The width w1 in the direction perpendicular to the optical axis of the highest step or the lowest step of at least one step unit in the stepped structure is approximately half of the average value w2 of two steps either side of the highest step or the lowest step in the direction perpendicular to the optical axis.