Optical pickup device and optical disk drive

An optical disk drive comprising:

• a laser source for emitting, to an optical disk, a laser beam having a wavelength λ1 and a laser beam having a wavelength λ2, which is longer than the wavelength λ1;
• a light receiver, for receiving laser beams having the wavelength λ1 and the wavelength λ2 that are reflected by the optical disk;
• a beam splitter, for directing, to the light receiver, the laser beams having the wavelength λ1 and the wavelength λ2 that are reflected by the optical disk;
• and
• an astigmatism generation element, located between the beam splitter and the light receiver, for generating the laser beams having the wavelength λ1 and the wavelength λ2, which are to be used for focusing control, by designating as the front of the light receiver a focal point on one of the intersecting cross sections that include the light axes of the laser beams, and by designating as the rear of the light receiver, a focal point on the other cross section,
• wherein the astigmatism generation element is an optical element, which is like a Fresnel lens, whose step depth is substantially a natural number times either the wavelength λ1 or the wavelength λ2.

An optical pickup device comprising:

• a laser source for emitting, to an optical disk, a laser beam having a wavelength λ1 and a laser beam having a wavelength λ2, which is longer than the wavelength λ1;
• a light receiver, for receiving laser beams having the wavelength λ1 and the wavelength λ2 that are reflected by the optical disk;
• a beam splitter, for directing, to the light receiver, the laser beams having the wavelength λ1 and the wavelength λ2 that are reflected by the optical disk;
• and
• an astigmatism generation element, located between the beam splitter and the light receiver, for generating the laser beams having the wavelength λ1 and the wavelength λ2, which are to be used for focusing control, by designating as the front of the light receiver a focal point on one of the intersecting cross sections that include the light axes of the laser beams, and by designating as the rear of the light receiver, a focal point on the other cross section;
• and
• a prism internally including the astigmatism generation element,
• wherein the astigmatism generation element is an optical element, which is like a Fresnel lens, whose step depth is substantially a natural number times either the wavelength λ1 or the wavelength λ2, and
• wherein a reflection face in a Fresnel lens shape of the astigmatism generation element is formed using a resin sealed inside the prism.