Diffraction Grating, Optical Pickup Device And Optical Disc Apparatus

An optical pickup device comprising:

• at least one semiconductor laser which emits a light beam;
• a first objective lens which focuses the light beam emitted from the at least one semiconductor laser onto a first optical disc;
• a second objective lens which focuses the light beam emitted from the at least one semiconductor laser onto a second optical disc;
• a grating which branches a light beam reflected from the second optical disc;
• an optical detector having a plurality of light receiving parts, which receives light beams branched by the grating;
• and
• an actuator which displaces the first and second objective lenses in a radial direction of the first optical disc and the second optical disc;
• wherein the grating has a first area on which a 0-order diffraction light beam and a +1-order diffraction light beam upon reflection at a track of the second optical disc enter, and a second area on which a 0-order diffraction light beam and a −1-order diffraction light beam upon diffraction through the track of the second optical disc enter, center parts of the first area and the second area being arranged to be spaced at a distance d in a direction perpendicular to the displacement direction.