Patent ID: 6839189

Claim:
An objective lens for being provided in an optical pickup device for carrying out a reproduction and/or a record of information for a first optical information storing medium having a protect substrate having a thickness of t 1 by using a first light source emitting a light having a wavelength of λ 1 , and for carrying out a reproduction and/or a record of information for a second optical information storing medium having a protect substrate having a thickness of t 2 which is more than t 1 , by using a second light source emitting a light having a wavelength of λ 2 which is more than λ 1 ; the objective lens comprising: an optical functional surface; wherein the optical functional surface is divided into at least two concentric optical functional regions which are arranged around an optical axis; a light flux passing through a central region which is one optical functional region including the optical axis, is used for the reproduction and/or the record of the information for both the first optical information storing medium and the second optical information storing medium; a light flux passing through a peripheral region which is another optical functional region arranged outside the central region, is mainly used for the reproduction and/or the record of the information for the first optical information storing medium; a diffractive structure is provided on the peripheral region; in case that the reproduction and/or the record of the information is carried out for the first optical information storing medium by using the first light source emitting the light having the wavelength of λ 1 , a diffraction order of a diffracted light having a maximum diffraction efficiency among a plurality of diffracted lights caused by the diffractive structure is k which is a natural number; and in case that the reproduction and/or the record of the information is carried out for the second optical information storing medium by using the second light source emitting the light having the wavelength of λ 2 , a relation between a diffraction efficiency E2(k) of a k-th order diffracted light caused by the diffractive structure and a diffraction efficiency E2(k−1) of a (k−1)th order diffracted light meets a following inequality: E 2( k −1)> E 2( k ).