Patent ID: 6856471
Filing Date: 2005-02-15
Classification: G11B

Abstract:
1. An objective optical element for use in an optical pickup apparatus which comprises a first light source to emit a light flux having a wavelength λ 1 for conducting recording or reproducing information for a first information recording medium with a transparent substrate having a thickness t 1 , a second light source to emit a light flux having a wavelength λ 2 (λ 1 <λ 2 ) for conducting recording or reproducing information for a second information recording medium with a transparent substrate having a thickness t 2 (t 1 <t 2 ), and a light converging system including the objective optical element to converge the light flux emitted from the first and second light sources onto an information recording plane through the respective transparent substrates of the first and second information recording mediums, the objective optical element comprising: an objective lens to converge the light flux emitted from the first and second light sources; and an optical functional surface to provide an optical action to the light flux and the optical functional surface including a common region including an optical axis and used for recording and/or reproducing information for both of the first and second information recording mediums and an exclusive region mainly used for recording and/or reproducing information for the first information recording medium; wherein the objective optical element forms a spot on a first recording medium with the diameter of the spot determined by an effective diameter and a focal length of the objective optical element, wherein when an infinite object distance light ray with a height h from the optical axis is emitted from the objective optical element, U is an angle formed by the emitted infinite object distance light ray and the optical axis and a sine condition unsatisfied-amount is defied by a formula of SC(h)=h/sinU−f(f is a focal length of the objective optical element when the first and second optical information recording medium are used respectively), a sign of a minimum sine condition unsatisfied-amount on the common region when the first optical information medium is used is a negative sign and a sign of a minimum sine condition unsatisfied-amount on the common region when the second optical information medium is used is a negative sign.