Patent ID: 7715297

Claim:
An optical pickup apparatus comprising: a laser diode to emit two light beams of different wavelengths; a diffraction grating to split a light beam from the laser diode into three discrete beams comprising one main beam and two sub beams; a beam splitter to reflect a light beam from the diffraction grating towards an optical disc and to transmit a reflected light beam from the optical disc; an objective lens to condense the reflected light beam from the optical disc; and a photo detector to photoelectrically convert three beam spots condensed by the objective lens into electric signals, wherein the diffraction grating comprises: a substrate to refract an input beam at a predetermined refractive index; a liquid crystal to refract the substrate refracted beam at differing refractive indexes and directions according to a track pitch of the optical disc; an electrode material to supply power to the liquid crystal; and a switch to control the power supply to the electrode material for selecting one of the differing refractive indexes to read/write information from/to the optical disc, wherein the electrode material comprises upper and lower electrode parts disposed at respective upper and lower parts of the liquid crystal, and one of the upper and lower electrode parts comprises a plurality of rectangular bar-shaped electrodes disposed laterally at predetermined distances from each other, and wherein the one of the upper and lower electrode parts comprises a first electrode layer formed of a plurality of the plurality of rectangular bar-shaped electrodes disposed at predetermined distances from each other, and a second electrode layer formed of a plurality of the plurality of rectangular bar-shaped electrodes disposed in parallel with electrodes of the first electrode layer but having different widths and directions from the electrodes of the first electrode layer.