Patent ID: 8477580
Filing Date: 2013-07-02
Classification: G11B

Abstract:
1. An objective lens, which is provided in an optical pickup including a spherical aberration correction mechanism which performs a spherical aberration correction with respect to laser light applied to a recording layer of an optical recording medium, having the recording layer on which information can be recorded at a plurality of positions in a depth direction, via the objective lens, and a tilt correction unit which varies a lens tilt angle which is a tilt angle of the objective lens, thereby performing a tilt correction, wherein, when a third-order spherical aberration variation (λrms) corresponding to an error of a condensed position of the laser light with respect to a predetermined reference layer position set inside the recording layer is denoted by ΔSA, the lens tilt angle (radian) is denoted by Ltilt, a third-order comatic aberration variation (λrms) generated by the lens tilt angle Ltilt is denoted by ΔCA, and a relationship therebetween is given by ΔCA/Ltilt=α*ΔSA, the objective lens is designed such that a value of α has a value in an allowable difference range which has an ideal value indicated by α=−6.32·NA (where NA is an effective numerical aperture of the objective lens), as a reference, and has a value in the allowable difference range set based on the third-order comatic aberration variation ΔCA and a Marechal criterion when the third-order spherical aberration variation ΔSA is the maximum and the lens tilt angle is the maximum.