| 摘要 |
An optical pickup device comprising first and second light sources for emitting beams of light of wavelengths lambda 1, lambda 2, a focusing optical system, and an optical sensor for recording/reproducing information about optical information recording media of at least two types, wherein a first optical information recording medium has a necessary numeric aperture larger than that of a second optical information recording medium, the focusing optical system splits a beam of light into k (k>4) annular beams, the first and <i>k</i>-th beams of the first-wavelength beam are focused onto the information recording surface of the first optical information recording medium, at least two beams out of the second to (<i>k-1</i>)-th beams of the first-wavelength beam have the apparent best image plane position different of that of the first and <i>(k</i>-th beams, and the optical pickup device has an optical element so formed that the wave aberrations of the light in the first to <i>k</i>-th beams of the first-wavelength beam passing through the necessary numerical aperture of the first optical information recording medium are generally integral multiples of lambda 1 in the best image plane position of the first and <i>k</i>-th beams.
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