Patent ID: 7206277

Claim:
An optical pickup device having a function to detect focal error of a light beam, comprising: an irradiating optical system for converging a light beam to form a spot on a recording surface via a light-transmitting layer of an optical recording medium; a photodetection optical system for converging return light reflected and returned from the spot onto a photodetector; a diffractive optical element disposed on an optical axis of the return light in the photodetection optical system and provided with an annulus annularly extracting from the return light ray components in a vicinity of a predetermined radius on a pupil on an emitting pupil surface of the irradiating optical system, the wave aberration distribution being affected by the wave aberration generated in the optical system wherein the diffractive optical element has an internal area defined inside the annulus and an external area defined outside the annulus within the return light; first light receiving components provided with the photodetector and receiving the ray components transmitted and extracted by the annulus; and a focal error detecting circuit connected to the first light receiving components and detecting a focal error of the light beam on the basis of a photoelectrically converted output obtained from the outputs of the photodetector.