Diffraction type lens which converges two wavelengths of light

摘要

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 lambda₁ of light and a greater converging action with respect to a wavelength lambda₂ of light, and the other surface formed with a zone plate exhibiting a smaller converging action with respect to the wavelength lambda₂ of light and a greater converging action with respect to the wavelength lambda₁ of light. The substrate is transparent to the wavelengths lambda₁ and lambda₂ of light.