DIFFRACTION OPTICAL ELEMENT, OBJECT OPTICAL SYSTEM, OPTICAL PICKUP DEVICE AND OPTICAL INFORMATION RECORDING/REPRODUCING DEVICE

摘要

A second diffraction structure, having an optical path length ratio deltaPhiB12 between wavelength lambda1 and wavelength lambda2 that is different from an optical path length ratio deltaPhi A12 in the above first diffraction structure, is provided in a diffraction optical element, and the difference in diffraction action between the first and second diffraction structures is used to thereby be able to control or minimize the wavelength-dependency of spherical aberration in the first diffraction structure. Therefore, it is possible to improve yield in bluish-purple laser light source mass production and reduce the production costs of a bluish-pusple laser light source and an optical pickup device.