| 摘要 |
An objective lens, for an optical information read/write device that performs read/write operations on each of a plurality of optical discs using a corresponding one of three laser beams having first, second, and third wavelengths λ1, λ2, and λ3 (nm) satisfying a relationship λ1<λ2<λ3, respectively, includes a phase shift structure having a plurality of ring-shaped refractive surface zones into which at least one surface of the objective lens is concentrically divided. The objective lens is made of material with an Abbe number &ngr;d satisfying a condition 40≦̸&ngr;d≦̸80. The phase shift structure has a step between each couple of the adjacent refractive surface zones that gives an optical path difference to an incident laser beam, so that a condition 2N+1.00<|&Dgr;OPD/λ1|<2N+1.30 is satisfied, where &Dgr;OPD represents the optical path difference (nm) that the step gives to the laser beam with the first wavelength, and N represents a non-negative integer.
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