Patent ID: 7177089

Claim:
An objective for use in an optical pickup apparatus which conducts reproducing and/or recording information for a first optical information recording medium comprising a first protective substrate whose thickness is t1 by using a first light flux having a wavelength λ 1 emitted from a first light source, conducts reproducing and/or recording information for a second optical information recording medium comprising a second protective substrate whose thickness is t2 (t1<=t2) by using a second light flux having a wavelength λ 2 (1.5·λ 1 <λ 2 <1.7·λ 1 ) emitted from a second light source, and conducts reproducing and/or recording information for a third optical information recording medium comprising a third protective substrate whose thickness is t3 (t2<t3) by using a third light flux having a wavelength: λ 3 (1.9·λ 1 <λ 3 <2.1·λ 1 ) emitted from a third light source, the objective comprising: a first diffractive structure, and a second diffractive structure, wherein the first diffractive structure makes a light amount of p-th ordered diffracted ray (p is an integer except 0) of the first light flux larger than a light amount of any other ordered diffracted ray of the first light flux, makes a light amount of p-th ordered diffracted ray of the second light flux larger than a light amount of any other ordered diffracted ray of the second light flux, and makes a light amount of p-th ordered diffracted ray of the third light flux larger than a light amount of any other ordered diffracted ray of the third light flux, and wherein the second diffractive structure makes a light amount of 0-th ordered diffracted ray of the first light flux larger than a light amount of any other ordered diffracted ray of the first light flux, makes a light amount of q-th ordered diffracted ray (q is an integer except 0 and p=q or p≠q) of the second light flux larger than a light amount of any other ordered diffracted ray of the second light flux, and makes a light amount of 0-th ordered diffracted ray of the third light flux larger than a light amount of any other ordered diffracted ray of the third light flux.