Compatible objective lens

摘要

A compatible objective lens for focusing a first laser beam and a second laser beam having a shorter wavelength than the first laser beam on a first disk substrate corresponding to the first wavelength and a second disk substrate which is thinner than the first disk substrate and corresponds to the second wavelength. The first substrate may be a CD substrate, and the second substrate may be a DVD substrate. The lens has a curvature optimized in the thickness of said first disk substrate. An integral annular phase shifter (101) shifts the phase of the first laser beam without shifting the phase of the second laser beam.