Optical pickup device

An optical pickup device which performs at least one of writing information in and reading information out of an optical information storage medium, said optical pickup device comprising:

• a light source which emits a first light at a first wavelength, a second light at a second wavelength and a third light at a third wavelength;
• an optical path combining unit operable to combine vectors of the first, second and third light emitted by said light source, and to match optical axes of the first light and the third light;
• a light collection unit operable to condense the light from said optical path combining unit into the optical information storage medium;
• a first diffraction element operable to diffract reflected light of the first light reflected from the optical information storage medium into + first-order diffracted light, − first-order diffracted light, + second-order diffracted light and − second-order diffracted light, and to diffract reflected light of the second light reflected from the optical information storage medium into the + first-order diffracted light and the − first-order diffracted light, and to diffract reflected light of the third light reflected from the optical information storage medium into the + first-order diffracted light and the − first-order diffracted light;
• a first photo detector which receives the +second-order diffracted light of the first light, the + first-order diffracted light of the second light and the + first-order diffracted light of the third light from said first diffraction element;
• a second photo detector which receives the − second-order diffracted light of the first light and the − first-order diffracted light of the third light from said first diffraction element;
• a third photo detector which receives the − first-order diffracted light of the second light from said first diffraction element;
• and
• a prevention unit formed between said first diffraction element and said first photo detector, said second photo detector and said third photo detector, and which prevents irradiation of the + first-order diffracted light and the − first-order diffracted light of the first light diffracted by said first diffraction element into said first photo detector, said second photo detector, and said third photo detector.