Patent ID: 7872958

Claim:
An optical element for an optical information recording/reproducing device which executes information reading and/or writing on multiple types of optical discs having different data densities by selectively using first through third light beams having first through third wavelengths λ1-λ3 (λ1<λ2<λ3) respectively, wherein: at least one side of the optical element is provided with a step structure including a plurality of concentric refracting surfaces and a plurality of steps formed between adjacent ones of the plurality of concentric refracting surfaces; the plurality of steps include first steps each giving a first optical path length difference specified by a first optical path difference function, second steps each giving a second optical path length difference specified by a second optical path difference function different from the first optical path difference function, and special steps each giving an optical path length difference obtained by one of a sum of the first and second optical path length differences and a difference between the first and second optical path length differences; and each of annular zone widths between adjacent ones of the plurality of steps is set at 10 times the first wavelength or more.