Patent ID: 7197004

Claim:
An optical pick-up apparatus which optically records information into an optical recording medium and/or reproduces information from an optical recording medium, comprising: a light source for irradiating light; a collimator lens for changing the light irradiated from the light source to a substantially parallel light; a diffraction grating for diffracting the light irradiated from the light source at least to zero-order diffraction light, plus (+) first-order diffraction light and minus (−) first-order diffraction light, and for providing a phase difference to part of the + and −(±) first order diffraction light; light converging means for converging the zero-order diffraction light and the ±first order diffraction light onto the optical recording medium; light separating means, disposed between the light source and the light converging means, for transmitting and reflecting the zero-order diffraction light and the ±first order diffraction light; and light detecting means including a plurality of light receiving elements, for receiving the zero-order diffraction light and the ± first order diffraction light reflected by the optical recording medium, wherein in the diffraction grating, a diffraction area which provides a phase difference to the ±first order diffraction light and a diffraction area which provides no phase difference to the ±first order diffraction light are alternately disposed adjacent to each other in an extension direction of a grating groove, and wherein the diffraction grating is formed so that a width W 1 which is a length of a diffraction area which provides a phase difference in the extension direction of the grating groove and a width W 2 which is a length of a diffraction area which provides no phase difference in the extension direction of the grating groove, meet the following formula (W 1 =W 2 =D/m), where D denotes an effective diameter of a light beam irradiated from the light source and irradiates to the diffraction grating, and m denotes a number of divisions into which the effective diameter D of the light beam is equally divided in a grating groove direction (m is an integer of 3 or more).