Patent ID: 6337841
Filing Date: 2002-01-08
Classification: G02B,G11B

Abstract:
An apparatus, comprising:a first optical source emitting a first light beam having a predetermined wavelength; a second optical source emitting a second light beam having a longer wavelength relative to the first light beam; an optical path changing means for changing the traveling path of an incident light beam; an objective lens for condensing the first light beam and the second light beam onto optical discs having different thicknesses; an optical diffraction means having a first region which directly transmits the first and second light beam 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 towards 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 said optical discs and passed through said optical path changing means.