Patent ID: 8159908

Claim:
A photodetector for, when light emitted from a two-wavelength light source is divided into at least three light components to be reflected by an optical recording medium, detecting the reflected light components, the photodetector comprising: a first detector divided into no more than eight sections detecting the at least three light components reflected by the optical recording medium to convert the light components into a first set of electrical signals; a first calculating portion calculating a first tracking error signal from the first set of electrical signals converted by the first detector by a differential push-pull method; a second calculating portion calculating a first focusing error signal by an astigmatism method and calculating a second tracking error signal by a differential phase detection method from the first set of electrical signals converted by the first detector; a second detector divided into four sections detecting the at least three light components reflected by the optical recording medium to convert the at least three light components into a second set of electrical signals; and a third calculating portion calculating a second focusing error signal by the astigmatism method and calculating a third tracking error signal by the differential phase detection method from the second set of electrical signals converted by the second detector, wherein the first detector includes: a first central sensor having a region divided vertically and horizontally into four sub regions detecting a central light component among the at least three light components reflected by the optical recording medium to convert the central light component into the first set of electrical signals; a first peripheral sensor having a region divided vertically or horizontally into two sub regions detecting a first peripheral light component among the at least three light components reflected by the optical recording medium to convert the first peripheral light component into the first set of electrical signals; and a second peripheral sensor having a region divided vertically or horizontally into two sub regions detecting a second peripheral light component among the at least three light components detected by the optical recording medium to convert the second peripheral light component into the first set of electrical signals.