Optical diffraction grating element, and optical pick-up device and optical scan device that respectively comprise optical diffraction grating element

Abstract From the Canadian patent

An optical diffraction grating element comprising diffraction gratings having a configuration in which grooves and flat lands each positioned between the adjacent grooves are successively alternately formed wherein the diffraction gratings have the same groove depth, groove width and groove tilt angle in order to obtain a constant 0th-order diffraction efficiency and first-order diffraction efficiency in the optical diffraction grating element while the pitches of the diffraction gratings are made different by setting a different land width for each diffraction grating. An optical pick-up device comprising an optical system including a light source and an optical diffraction grating element …