| 摘要 |
<P>PROBLEM TO BE SOLVED: To perform detection of a tracking error with sufficient precision by making diffracted light intensity ratio properly and raising the use efficiency of a laser in an optical pickup using optical beams of a plurality of kinds of different wavelengths. <P>SOLUTION: A diffractive optical element 4 which is prepared in the optical pickup which condenses an optical beam of a first wavelength and an optical beam of a second wavelength which is longer than the first wavelength to an optical disk 8 with an objective lens 7, and detects a return optical beam reflected with an optical disk by a photo detector 10A, divides the optical beam of the first and the second wavelengths. The diffractive optical element 4 has; a first diffraction region which includes an optical axis and in which a first grid structure comprising periodical irregularities is formed; and a second diffraction region which is prepared outside the first diffraction region and in which a second grid structure comprising periodical irregularities of a different shape from the first grid structure is formed. The diffraction efficiency of primary diffracted light of optical beam of the above first wavelength in the above second diffraction region is made higher than the diffraction efficiency of the primary diffracted light of optical beam of the above first wavelength in the above first diffraction region. <P>COPYRIGHT: (C)2008,JPO&INPIT |
