Diffraction grating and optical pickup apparatus with diffracting grating

摘要

An optical pickup apparatus in which light from a light source is led to an information medium and reflected light from the information medium is led to a hologram to be incident as a +1st order diffraction beam on a photodetector to obtain information signals. The hologram has a stair-like cross-sectional configuration, and a ratio of the width of a step of the stair-like cross-sectional configuration relative to a grating pitch of the hologram is arranged to vary in accordance with a position within a surface of the hologram.