Patent ID: 6542314
Filing Date: 2003-04-01
Classification: G11B

Abstract:
An objective lens for optical recording media, which, when recording or reproducing information for a first optical recording medium corresponding to a first numerical aperture and a first wavelength and a second optical recording medium corresponding to a second numerical aperture and a second wavelength, converges said wavelengths of light in use to respective desirable positions;wherein one surface of said objective lens is provided with a zonal part which acts so as to apparently cancel the quantity of light having one wavelength &lgr;1 in an outer peripheral portion of a luminous flux thereof due to an interference effect but keep the quantity of light having the other wavelength &lgr;2 in said outer peripheral portion thereof; wherein said zonal part has a step by which light supposed to pass a position corresponding to said zonal part if said zonal part does not exist and light passing a position at which said zonal part is formed if said zonal part exists generate therebetween a phase difference satisfying the following conditional expressions (1) and (2): &Dgr;&lgr;1=(2m+1)&lgr;1/2+&dgr;1,â€ƒâ€ƒ(1) &Dgr;&lgr;2=n&lgr;2+&dgr;2â€ƒâ€ƒ(2) where&Dgr;&lgr;1 is the phase difference at the wavelength &lgr;1 between the light supposed to pass the position corresponding to said zonal part if said zonal part does not exist and the light passing the position at which said zonal part is formed if said zonal part exists; &Dgr;&lgr;2 is the phase difference at the wavelength &lgr;2 between the light supposed to pass the position corresponding to said zonal part if said zonal part does not exist and the light passing the position at which said zonal part is formed if said zonal part exists; m and n are integers; |&dgr;1|<0.2 &lgr;1; and |&dgr;2|<0.2 &lgr;2; and wherein the numerical aperture at a boundary position of said step has a value between said first and second numerical apertures.