Patent ID: 8339923

Claim:
An objective optical element for use in an optical pickup device comprising a first light source emitting a first light flux with a wavelength λ 1 (375 nm≦λ 1 ≦435 nm), a second light flux emitting a second light flux with a wavelength λ 2 (λ 1 <λ 2 ), and an objective optical element, wherein the optical pickup device records and/or produces information by converging the first light flux onto an information recording surface of a first optical disc including a protective layer with a thickness t 1 and converging the second light flux onto an information recording surface of a second optical disc including a protective layer with a thickness t 2 (t 1 <t 2 ) to record and/or reproduce information, using the objective optical element, wherein the objective optical element is a single lens and comprises a central area including an optical axis and a peripheral area arranged around the central area, wherein a central-area diffractive structure is arranged in the central area, the first light flux which has passed through the central area is converged on the information recording surface of the first optical disc so that information can be recorded and/or reproduced, the second light flux which has passed through the central area is converged on the information recording surface of the second optical disc so that information can be recorded and/or reproduced, the first light flux which has passed through the peripheral area is converged on the information recording surface of the first optical disc so that information can be recorded and/or reproduced, the second light flux which has passed through the peripheral area is not converged on the information recording surface of the second optical disc so that information can be recorded and/or reproduced, and the objective optical element satisfies the following expressions, where SA3(λ 11 ), SA5(λ 11 ), SA3(λ 12 ), and SA5(λ 12 ) are third-order spherical aberrations in units of λrms and fifth-order aberrations obtained when light fluxes with two different wavelengths λ 11 and λ 12 which are within the range of the wavelength λ 1 and satisfy λ 11 <λ 12 and λ 12 −λ 11 =5 nm enter the objective optical element and wavefront aberrations are measured: 0.18>ΔSA3>ΔSA5>0 (1) wherein ΔSA3=|SA3(λ 12 )−SA3(λ 11 )| and ΔSA5=|SA5(λ 12 )−SA5(λ 11 )|.