Patent ID: 7933188

Claim:
An optical pickup comprising: a laser beam source; an irradiating beam focusing optical system that focuses a laser beam from the laser beam source on one recording layer of a multi-layer optical information storage medium; and a detecting optical system that detects reflected light reflected from the recording layer of the multi-layer optical information storage medium, wherein: the detecting optical system includes a reflecting light condenser lens that converges the reflected light from the recording layer, a reflecting plane provided to a minimum spot position of the reflected light from the recording layer out of the reflected light converged by the reflected light condenser lens, a grating which is installed between the reflected light condenser lens and the reflecting plane with the grating including an optical axis and attenuates the quantity of reflected light from an adjacent layer except the corresponding layer or changes a direction of the reflected light, and a photodetector that detects the reflected light; reflected light reflected by the reflecting plane is detected on the photodetector; the grating is overlapped with at least one of minimum spot positions by the reflected light condenser lens of the reflected light from the adjacent layer; and the grating is installed with a direction of grooves of the grating perpendicular to the optical axis or inclined.