Patent ID: 8451703

Claim:
An optical pickup comprising: a light source; an optical system for irradiating a recording medium including a plurality of recording layers with light from the light source; a diffraction optical element that divides light reflected from the recording medium into a plurality of optical fluxes and diffracts the fluxes; and an optical detector receiving the optical flux diffracted by the diffraction optical element; wherein the optical detector includes a light receiving element detecting a focus error signal, a longitudinal direction of the light receiving element being arranged coinciding with a circumferential direction of the recording medium, or arranged inclined to a circumferential or radial direction; wherein the focus error signal is detected from a region other than a central region of the reflected light and other than a push-pull region of the diffraction optical element; and wherein the pickup is arranged such that 0≦φ≦20, where an angle θ is between an axis of a circumferential direction passing through a center of the reflected light and a line passing through the center of the reflected light and a center of a circular arc of the reflected light in a focus error detection region, and an inclination φ is of the longitudinal direction of the light receiving element with reference to the axis of the circumferential direction.