Patent ID: 6898169

Claim:
An optical pickup head device comprising: a light source for emitting a light beam; a diffraction means for diffracting the light beam from the light source into a plurality of beams of zero-order diffracted light and at least first-order diffracted light; a convergence means for converging the beams from the diffraction means on an optical recording medium; a beam splitting means for splitting the beams reflected from the optical recording medium; and a photodetection means for receiving the beams from the beam splitting means and outputting a signal that corresponds to an amount of light received, wherein the optical recording medium comprises tracks for recording information, the diffraction means comprises grating patterns with a nonuniform period or phase, a size of the at least first-order diffracted light converged on the optical recording medium is larger in a direction parallel to a tangent to the track than in a direction perpendicular to the tangent, and P 1 /P 0 >PW 2 /PW 1 is established, where PW 1 represents power of the zero-order diffracted light converged on the optical recording medium that is required to record information on the optical recording medium, PW 2 represents maximum power of the zero-order diffracted light converged on the optical recording medium that allows information recorded on the optical recording medium to be reproduced without being erased, P 0 represents a light amount of the zero-order diffracted light converged on the optical recording medium, and P 1 represents a light amount of one of the at least first-order diffracted light converged on the optical recording medium.