Diffractive optical element and optical pickup

An optical pickup comprising:

• a laser light source for emitting first laser light having a first wavelength as a center wavelength, second laser light having a second wavelength longer than the first wavelength as a center wavelength, and third laser light having a third wavelength longer than the second wavelength as a center wavelength;
• an objective lens for focusing the first laser light, the second laser light, and the third laser light onto the optical disc;
• a servo mechanism for changing the position of the objective lens;
• an optical element disposed on a light path of laser light reflected from an optical disc onto which one of the first laser light, the second laser light, and the third laser light is directed, the optical element astigmatizing the first to third laser lights;
• a diffractive optical element for causing one specific laser light or two specific laser lights of the first to third laser lights astigmatized by the optical element to diffract in specific diffraction angles;
• and
• a photodetector for detecting the first diffracted light as a diffracted light of the first laser light that exits the diffractive optical element, the second diffracted light as a diffracted light of the second laser light that exits the diffractive optical element, and the third diffracted light as a diffracted light of the third laser light that exits the diffractive optical element,
• wherein the diffractive optical element has:
• a first diffractive region and a second diffractive region which are different to each other and are formed by dividing the diffractive optical element by a straight line intersecting at an optical axis of the diffractive optical element;
• and
• the first diffractive region and the second diffractive region are structured so that the +1-order light output from the first diffractive region when laser light is incident on the first diffractive region propagates in a different direction from the +1-order light output from the second diffractive region when the same laser light is incident on the second diffractive region, and the −1-order light output from the first diffractive region when laser light is incident on the first diffractive region propagates in a different direction from the −1-order light output from the second diffractive region when the same laser light is incident on the second diffractive region.