Patent ID: 7298675

Claim:
An optical pickup for recording and/or reproducing data with respect to a multilayer recording medium having a plurality of recording layers, the optical pickup comprising: a light source emitting a beam having a predetermined wavelength; a diffraction unit separating the beam emitted from the light source into a main beam and a sub-beam; and a photo-detector having a main photodetector, detecting the main beam reflected from the multilayer recording medium, and a sub-photodetector detecting the sub-beam, wherein the main photodetector and the sub-photodetector are separated a predetermined distance Ds from each other so that a beam spot formed by the beam reflected from a defocus recording layer of the multilayer recording medium is not detected by the sub-photodetector, and wherein the predetermined distance Ds between the main photodetector and the sub-photodetector satisfies the following inequality: D s ≧A/ 2 +QR wherein “R” is a radius of the beam spot formed by the beam reflected from the defocus recording layer, “A” is a width of the sub-photodetector, and “Q” is a coefficient indicating an allowable range of a DC offset of a sub-push-pull signal, and wherein the coefficient Q is between 0.85-0.90 when the allowable range of the DC offset is not more than 5%.