OPTICAL PICKUP USED FOR BOTH DVD AND HIGH DENSITY DVD, AND APPARATUS FOR DETECTING SPHERICAL ABERRATION ACCORDING TO THE SAME

摘要

PURPOSE: An optical pickup used for both DVD and high density DVD, and an apparatus for detecting spherical aberration according to the same are provided to accurately compensate spherical aberration due to changes in thickness of a disk recording layer, and accurately detect a spherical aberration signal. CONSTITUTION: A dichroic filter(54) controls an aperture number to a laser beam for a high density DVD(Digital Versatile Disk) and an aperture number to a laser beam for a DVD to make the aperture numbers different from each other. A first hologram optical element(80) transmits the laser beam for a high density DVD and compensate spherical aberration for the laser beam for a DVD only. A first polarizing plate(70) transmits the laser beam for a high density DVD and executes a polarizing operation for the laser beam for a DVD only. A second hologram optical element(82) transmits the laser beam for a high density DVD, and compensate spherical aberration opposite to the first spherical aberration compensating element for the laser beam for a DVD only. A second polarizing plate(81) executes different polarizing operations to the laser beam for a high density DVD and the laser beam for a DVD.