/ Optical pickup apparatus for capable of detecting thickness variation of recording medium and/or compensating spherical abberation generated by thickness variation thereof

摘要

PURPOSE: An optical pickup device for detecting a change in thickness of a recording medium and capable of correcting a spherical aberration caused by the change in thickness is provided to operate detection signals output from a photo detector, to detect thickness changing signals, so that the thickness change of the recording medium is detected even in an optical system without an astigmatic lens. CONSTITUTION: A light source(51) generates and emits light beam. An objective lens(57) focuses the light beam incident from the light source, to form an optical spot on an information recording surface(50a) of a recording medium(50). An optical path conversion unit arranged on an optical path between the light source and objective lens converts a progress direction of the incident light. A photo detector(65) divides light beam reflected from the recording medium and passing the objective lens and optical path conversion unit, for detection. A thickness change detecting circuit(70) operates detection signals output from the photo detector, to detect a change in thickness(t) of the recording medium. The thickness of the recording medium refers to the thickness from a light incident surface(50b) of the recording medium to the information recording surface.