Objective lens and optical information recording/reproducing device having the same

摘要

There is provided an objective lens for information recording/reproducing for three types of optical discs, which includes a first area contributing to converging a third light beam onto a record surface of a third optical disc. The first area includes a phase shift structure having refractive surface zones concentrically formed about a predetermined axis. The phase shift structure includes first and second step groups. The first step group is configured such that an optical path length difference &Dgr;OPD1 (nm) given by each step of the first step group to a first light beam satisfies a condition: 2N1+1.10<|&Dgr;OPD1/λ1|<2N1+1.40, where N1 is an integer or zero, and the second step group is configured such that an optical path length difference &Dgr;OPD2 (nm) given by each step of the second step group to the first light beam satisfies a condition: 2N2−0.10<|&Dgr;OPD2/λ1|<2N2+0.10, where N2 is an integer.