GRATING ELEMENT, OPTICAL PICKUP OPTICAL SYSTEM AND METHOD OF DESIGNING GRATING ELEMENT

A grating element is provided with diffraction members wherein protrusions and recesses are periodically arranged, respectively, on one surface of each of transparent substrates. The diffraction members are laminated in the substantially perpendicular direction to the transparent substrates, the protrusions of the diffraction members are made of a dielectric multilayer film, and the dielectric multilayer film has dielectric films of two or more types laminated in the substantially perpendicular direction on the transparent substrates. The wavelengths of laser beams diffracted at predetermined diffraction efficiencies by the diffraction members are different from one another.