Patent ID: 7505390

Claim:
A compatible optical pickup which can be compatibly used for first through third recording media having different recording densities and formats, comprising: a first light source which emits a first light beam having a first wavelength suitable for the first recording medium; a twin light source which emits second and third light beams respectively having second and third wavelengths suitable for the corresponding second and third recording media; a plate-type beam splitter which transmits and reflects the second and third light beams in a predetermined ratio; a first objective lens which condenses the first light beam to form a light spot for recording and/or reproduction of the first recording medium; a second objective lens which condenses the second and third light beams to form light spots for recording and/or reproduction of the received one of the second and third recording media; an actuator which drives the first and second objective lenses; a first photo-detector which receives the first light beam reflected from the first recording medium to detect an information signal and/or an error signal; and a second photo-detector which receives the second and third light beams reflected from the received one of the second and third recording media to detect information signals and/or error signals, wherein the first objective lens forms a first numerical aperture for use with the first recording medium and a second numerical aperture other than the first numerical aperture for use with the second recording medium, the second objective lens forms a third numerical aperture which is other than the first and second numerical apertures for use with the third recording medium, WD1 is a working distance of one of the first and second objective lenses which has a short working distance, WD2 is a working distance of the other one of the first and second objective lenses which has a long working distance, the first and second objective lenses are installed to satisfy the below relationship so as to prevent the one objective lens having the short working distance from contacting the received one of the first through third recording media during loading of the received recording medium and while allowing operation of the other one of the first and second objective lenses having the long working distance: WD2≧WD1, a basic separating distance of the one objective lens relative to the corresponding one of the first through third recording media is WD1+α, and α=|WD2−WD1|×(0.1˜1.0), and at least one of the first and second objective lenses is formed so that a wavefront aberration occurring mainly due to a tilt of the objective lens and a wavefront aberration occurring mainly due to a tilt of light incident on the objective lens become a same type of aberration.