Patent ID: 7242659

Claim:
An optical pickup for a recording medium, comprising: a light source to generate and emit a light beam; an objective lens arranged to focus the light beam from the light source to form a light spot on the recording medium; an optical path changer disposed on an optical path between the light source and the objective lens, for altering a traveling path of the light beam incident on the recording medium; a light beam division and detection unit arranged to detect the incident light beam passed through the objective lens and the optical path changer after being reflected from the recording medium, wherein the light beam division and detection unit comprises a photo-detector comprising first, second, and third light receiving portions to divide the incident light beam into a first light beam portion aligned with an optical axis, and second and third light beam portions at respective side of the first light beam portion, and to photo-electrically convert the first, second, and third light beam portions into the first, second, and third detection signals; and a thickness variation detection circuit arranged to detect a variation in thickness of the recording medium by subtracting the sum of the second and third detection signals from the first detection signal, and to output a thickness variation signal indicative thereof.