Patent ID: 7990831

Claim:
An optical pickup device configured to perform read/write operations for a first optical disk, a second optical disk, and a third optical disk, comprising: a first light source configured to emit first light with a first wavelength in use of the first optical disk; a second light source configured to emit second light with a second wavelength longer than the first wavelength in use of the second optical disk; a third light source configured to emit third light with a third wavelength longer than the second wavelength in use of the third optical disk; an objective lens having a step structure on at least one surface thereof, the step structure being formed with a plurality of refractive surfaces as concentrically-divided annular zones so as to provide incident light with a predetermined optical path length difference at a step between any adjacent two of the refractive surfaces, the objective lens being configured to converge the first light, the second light, and the third light onto the first optical disk, the second optical disk, and the third optical disk, respectively; at least one first coupling lens configured to make the first light and the second light incident onto the objective lens as converged light; a second coupling lens configured to make the third light incident onto the objective lens as diverging light; and a liquid crystal aberration correcting element provided on a common optical path between one of the at least one first coupling lens and the second coupling lens and the objective lens, the liquid crystal aberration correcting element being configured with a plurality of concentrically-divided areas so as to provide incident light with a predetermined optical path length difference in each of the areas and correct aberration, wherein a following condition is satisfied: NA1>NA3, and NA2>NA3, where NA1 represents a numerical aperture required for use of the first optical disk, NA2 represents a numerical aperture required for use of the second optical disk, and NA3 represents a numerical aperture required for use of the third optical disk, wherein the step structure includes a first area required for ensuring NA3, the first area being formed to provide incident light, at each step therein, with an optical path length difference substantially twice as long as the first wavelength, and wherein the objective lens is disposed so as to satisfy following conditions (1), (2), and (3): 0.05 <f 1 ×M 1<0.20 (1) 0.05 <f 2× M 2<0.20 (2) −0.23 <f 3 ×M 3<−0.03 (3) where f1 and M1 represent a focal length and an imaging magnification of the objective lens in use of the first optical disk, respectively, f2 and M2 represent a focal length and an imaging magnification of the objective lens in use of the second optical disk, respectively, and f3 and M3 represent a focal length and an imaging magnification of the objective lens in use of the third optical disk, respectively.