Patent ID: 7369466

Claim:
An optical pickup apparatus comprising: a light source unit having a holder in which an optical module having first and second light sources for emitting light having different wavelengths and a grating are installed together; an optical path changer for changing a path of the light emitted from the first or second light sources; an object lens for focusing light passing through the optical path changer on a relatively thin disc or a relatively thick disc; and a photodetector unit comprising: a first photodetector having a first main photodetector, a first sub-photodetector, and a second sub-photodetector for receiving light diffracted into three beams by the grating and reflected by the relatively thin disc and converting the received light into an electrical signal; and a second photodetector having a second main photodetector, a third sub-photodetector, and a fourth sub-photodetector for receiving light diffracted into three beams by the grating and reflected by the relatively thick disc and converting the received light into an electrical signal; wherein beams focused on the first sub-photodetector and the second sub-photodetector are used to control the phases of the three beams with respect to the relatively thick disc.