Patent ID: 7180668

Claim:
An optical pickup device comprising: a light source for emitting light of a predetermined wavelength; an objective lens for condensing the light beam emitted from the light source onto an optical disc and condensing a return light beam from the optical disc; a composite optical element having a diffraction element for transmitting the light beam emitted from the light source and diffracting the return light beam from the optical disc, and light splitting means arranged at a position where the return light beam diffracted by the diffraction element is incident and adapted for splitting the return light beam into a plurality of beams; and light receiving means for receiving each return light beam split by the light splitting means, in a plurality of light receiving areas, in order to acquire a focusing error signal, wherein the prism is formed in a substantially four-sided pyramidal shape and quadrisects the return light beam diffracted by the diffraction element, wherein the composite optical element further comprises another diffraction element provided on an optical path between the light source and the diffraction element and adapted for trisecting the light beam emitted from the light source into zeroth-order light, plus-first-order light and minus-first-order light, and the light receiving means receives the zeroth-order light split by said another diffraction means, of the return light beams split by the light splitting means, in order to acquire a focusing error signal, and receives the plus-first-order light and the minus-first-order light split by said another diffraction element in order to acquire a tracking error signal, wherein the prism is formed in a substantially four-sided pyramidal shape and quadrisects the return light beam diffracted by the diffraction element.