| 摘要 |
PROBLEM TO BE SOLVED: To separately converge two kinds of light having different wavelength to a corresponding recording surface in a state where aberration is satisfactorily corrected by selecting lens forming materials so that the refractive indexes of two lenses may be nearly the same with reference to one of two kinds of light having different wavelength, and selecting the shape of the joined surface of two lenses, as for an objective lens for severally condensing the two kinds of light to a prescribed position. SOLUTION: In the case of recording/reproducing a DVD 6A, for example, the laser light having the wavelength of 650 nm (λ1) emitted from a light source is made incident on the objective lens in a nearly collimated state, and in the case of recording/ reproducing a CD-R 6B, the laser light having the wavelength of about 780 nm (λ2) emitted from the light source is made incident on the objective lens in the nearly collimated state, and the incident laser light is converged on the recording surface of the DVD 6A or the CD-R 6B through the objective lens. The objective lens is constituted of a doublet with a biconvex lens 1 and a negative meniscus lens 2 and the refractive indexes of both lenses 1 and 2 with reference to the light having the wavelength of 650 nm (λ1) are set so that they may be nearly equal. |
