Patent ID: 6781943
Filing Date: 2004-08-24
Classification: G02B,G11B

Abstract:
An optical pickup device for conducting reproducing and/or recording of information in at least two kinds of optical information recording media, comprisinga first light source to emit light flux having a first wavelength (&lgr;1) in order to conduct reproducing and/or recording of the information in a first optical information recording medium having a first transparent substrate; a second light source to emit light flux having a second wavelength (&lgr;2) longer than the first wavelength in order to conduct reproducing and/or recording of the information of a second optical information recording medium having a second transparent substrate, where the thickness of the second transparent substrate is thicker than the thickness of the first transparent substrate; a converging optical system for converging the light flux having the first wavelength or the light flux having the second wavelength on the first information recording surface of the first optical information recording medium or on the second information recording surface of the second optical information recording medium; and an optical detector for receiving and detecting the light flux reflected by the first information recording surface or by the second information recording surface, wherein a required numerical aperture for the first optical information recording medium is larger than that for the second optical information recording medium; wherein the converging optical system comprises at least one optical element and the optical element has ring-shaped divided surfaces partitioned by stepped portions on at least one surface for dividing the light flux incident on the optical element into k (k&gE; 4) pieces of ring-shaped light flux in which light flux nearest to the optical axis of the optical element is regarded as the fist light flux and other light flux are called consecutively the second, the third - - - , and the k-th light flux toward the outer side in the direction perpendicular to the optical axis; wherein when conducting reproducing or recording of the first optical information recording medium, the first light flux and the k-th light flux among the light flux of the first wavelength having passed the ring-shaped divided surfaces are converged on the first information recording surface in order to conduct reproducing or recording of the information of the first optical information recording medium, a spherical aberration component of a wave front aberration is made 0.05&lgr;1 rms or less at a position of the best image plane, and at least two pieces of light flux among the light flux of the first wavelength from the second light flux to the (k-1)th light flux form an apparent best image plane at a position different from the position of the best image plane formed by the first light flux and the k-th light flux; wherein at the position of the best image plane of the first light flux and the k-th light flux, a wave front aberration of a ray in each light flux of the first wavelength from the first light flux to the k-th light flux passing in a required numerical aperture for the first optical information recording medium is made approximately mi&lgr;1, where mi an integer and i=1,2, - - - , k, and wherein when conducting reproducing or recording of the first optical information recording medium, at the position of the best image plane of the first light flux and k-th light flux, an amount of the wave front aberration (w1) of the ray in each light flux of the first wavelength from the first light flux to the k-th light flux passing in the required numerical aperture for the first optical information recording medium satisfies the following conditional formula: (mjâˆ’0.30)&lgr;11mi+0.30)&lgr;1.