DIFFRACTION OPTICAL DEVICE AND OPTICAL PICKUP DEVICE USING THE SAME

摘要

A diffractive optical element comprises a first diffraction surface that does not diffract a light beam having a first wavelength »1 nor a light beam having a third wavelength »3 and diffracts a light beam having a second wavelength »2 and a second diffraction surface that does not diffract the light beam having the first wavelength »1 nor the light beam having the second wavelength »2 and diffracts the light beam having the third wavelength. The first to third wavelengths are different from one another. The first and second diffraction surfaces satisfy the condition A / » ‰¥ 8 where A is the smallest pitch among the pitches each of which represents the width causing the phase difference of one wavelength when wave fronts nearest to each other are connected at the adjacent steps of the diffraction surface, and » is the wavelength of the diffracted light.