OPTICAL HEAD DEVICE, OPTICAL INFORMATION DEVICE AND INFORMATION PROCESSING DEVICE

摘要

An optical head device is provided with a light shielding area (7y) which is disposed in the path of a beam of reflection light that was reflected by the recording layer at which a blue light beam is collimated, and which shields reflection light that is reflected by at least two recoding layers and is incident in an area of an optical detector (9) where the reflection light reflected by at least two recoding layers mutually interferes if at least the two recording layers exist on the incident side or the side opposite the incident side of the blue light beam with respect to the recording layer on which the blue light beam is collimated. The light shielding area (7y) is not formed on the optical axis of the reflection light reflected by the recording layer at which blue light is collimated. The signal to noise ration of the signal output by the optical detector is thereby improved by this structure.