| 摘要 |
PROBLEM TO BE SOLVED: To condense an optical beam with high light use efficiency respectively on information recording surfaces of a plurality of optical recording media having transparent substrates with different thicknesses.SOLUTION: An objective lens includes an inner area in which two types of laser beams with different wavelengths are condensed on the information recording surfaces of two types of the corresponding optical recording media having transparent substrates with different thicknesses and an outer area in which one type of the laser beam is condensed on the information recording surface of the corresponding optical recording medium and the other laser beam is not condensed on the information recording surface of the corresponding optical recording medium. The inner area is divided into a plurality of sections, and an aspheric shape and adjacent bump are set for offsetting color aberration of the laser beams and spherical aberration due to the difference of thicknesses of the transparent substrates respectively. Out of wave front aberrations generated when the laser beams with different wavelengths are condensed on the information recording surfaces of the corresponding optical recording media, the maximum wave front aberration Wmax and minimum wave aberration Wmin are assumed and they meet the following equation, Wmax≤0.035 λRMS. |
