Objective lens for high-density optical focusing, and optical pickup adopting the same

摘要

A high-density focusing objective lens having a high numerical aperture (NA), which can be easily manufactured by an existing technique, and an optical pickup adopting the objective lens for use in high-density recording. The objective lens (155) includes: a first transmitting portion (156) placed at a relatively near-axis region from the optical axis, for divergently transmitting an incident beam; a first reflecting portion (157) for divergently reflecting the incident beam, facing the first transmitting portion (156); a second reflecting portion (158) formed at a relatively far-axis region around the first transmitting portion (156), for focusing and reflecting the light reflected from the first reflecting portion (157); and a second transmitting portion (159) formed at a relatively far-axis region around the first reflecting portion (157), for refracting and transmitting the light focused by the second reflecting portion (158), wherein the maximum angle alpha between the optical axis and the peripheral beam passing through the second transmitting portion (159) after having passed through the first transmitting portion (156) and been reflected by the first and second reflecting portions (157;158) satisfies the condition of 30 DEG ≤ alpha ≤ 65 DEG . The optical pickup further includes the previously mentioned objective lens (155) as a second objective lens, which is optionally placed into the optical path between a first objective lens and an optical medium. As a result, the NA of the objective lens unit can be increased up to 0.85 while the working distance d2 is maintained to be 2 mm.