Patent ID: 6493307
Filing Date: 2002-12-10
Classification: G11B

Abstract:
An objective lens for focusing a first laser beam having a first wavelength on a first substrate and focusing a second laser beams having a second wavelength which is different from said first wavelength on a second substrate having a different thickness from said first substrate,wherein said objective lens includes a phase shifter having a rectangular groove, wherein said objective lens with said phase shifter is made of one material, wherein said objective lens has an outside portion for focusing said first wavelength on said first substrate and an inside portion for focusing said second wavelength on said second substrate, and wherein aberration of a region of said phase shifter moves toward plus so that the aberration of said first wavelength approaches zero closer than an aberration without said phase shifter and aberration of a region of said phase shifter moves toward minus so that the aberration of said second wavelength approaches zero closer than an aberratio n without said phase shifter.