Patent ID: 7317672

Claim:
An optical head comprising: a semiconductor laser; an objective lens for focusing a light beam from the semiconductor laser onto an information recording medium; a light beam separator that is located between the semiconductor laser and the objective lens, includes interference regions for light that is reflected from the information recording medium and travels in a straight path and ±first-order diffracted light produced by information tracks of the information recording medium, and diffracts each of plural light beams in regions of the interference regions, where an amount of light is changed by a change in a relative angle between the information recording medium and the objective lens and by a shift of the objective lens in a radial direction of the information recording medium; a light-receiving element that receives the light beam that is reflected by the information recording medium and separated by the light beam separator, and converts the light beam to an electrical signal; and an arithmetic circuit that corrects a value of the electrical signal detected by the light-receiving element in accordance with a radial position signal corresponding to an amount of shift of the objective lens in the radial direction of the information recording medium, and detects the relative angle between the information recording medium and the objective lens or an amount of tilt of the information recording medium with respect to a predetermined reference plane.