Compatible optical pickup

Abstract

A compatible optical pickup capable of recording or reproducing information on or from compact disc (CD) family media such as CD rewritable (CD-RW) and digital versatile disc (DVD) by adopting a stepped planar lens having a plurality of gratings. The compatible optical pickup includes a first optical source for emitting a first light beam having a predetermined wavelength; a second optical source for emitting a second light beam having a long wavelength relative to the first light beam; an optical path changing element for changing the traveling path of an incident light beam; an objective lens for condensing the first and second light beams onto optical discs having different thicknesses, respectively; an optical diffraction element having a first region which directly transmits the first and second light beams incident thereto, and a second region bounding the first region, which directly transmits the incident first light beam and diffractingly transmits the second light beam toward an optical axis; and a photodetector for detecting an information signal and an error signal from the first and second light beam which have been reflected by the optical discs and passed through the optical path changing element. Also, the optical diffraction element is a stepped planar lens in which one or more stepped pattern periods each having a plurality of annular gratings are arranged in the second region, wherein the depths of the gratings become smaller moving away from the optical axis, and the maximum depth thereof is a predetermined value.

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