A diffraction type lens in an optical pickup apparatus for recording and reproducing
two or more kinds of optical recording media is constituted by a substrate having
one surface formed with a zone plate exhibiting a smaller converging action with
respect to a wavelength 1 of light and a greater converging action
with respect to a wavelength 2 of light, and the other surface
formed with a zone plate exhibiting a smaller converging action with respect to
the wavelength 2 of light and a greater converging action with
respect to the wavelength 1 of light. The substrate is transparent
to the wavelengths 1 and 2 of light.
