Patent ID: 7450487

Claim:
An optical pickup apparatus comprising a laser diode (LD) for emitting two light beams of different wavelengths, a diffraction grating for splitting a laser beam from the LD into three discrete beams, namely one main beam and two sub beams, a beam splitter for reflecting a beam off of the diffraction grating towards an optical disc and transmitting a reflected beam from the optical disc, an objective lens for condensing the reflected light transmitted through the beam splitter, and a photo detector for photoelectrically transforming the one main beam and two sub beam spots condensed by the objective lens into electric signals, wherein the photo detector is comprised of: a substrate for transmitting the one main beam and two sub beams reflected from the optical disc; a liquid crystal for refracting the two sub beams, that are transmitted through the substrate, at different refractive indexes according to the wavelength of a laser beam outputted from the laser diode; an electrode material for supplying power to the liquid crystal; a switch for adjusting the magnitude of an applied voltage to the electrode material; and a light receiving element on which the main beam and the refracted sub beams while transmitting through the substrate and the liquid crystal are projected and transformed into electric signals.