| 摘要 |
<P>PROBLEM TO BE SOLVED: To converge light beams on an information recording surface with high light utilization efficiency for two or more kinds of optical recording media for which the thickness of a transparent substrate is different. <P>SOLUTION: When a DVD for which the thickness t<SB>1</SB>of a DVD substrate 2 is 0.6 mm is mounted on an optical disk device, the light beam 4 of a wavelength λ<SB>1</SB>=655 nm is used as the luminous flux of a numerical aperture NA=0.63 and converged on the information recording surface 2a of the DBD substrate 2. Also, when a CD for which the thickness t<SB>2</SB>of a CD substrate 3 is 1.2 mm is mounted on the optical disk device, the light beam 5 of the wavelength λ<SB>2</SB>=790 nm is effectively used as the luminous flux for which the numerical aperture is roughly 0.45 and converged on the information recording surface 3a of the CD substrate 3. Though wave front aberration by the difference of the thickness of the substrates 2 and 3 of the DVD and the CD is generated, it is offset by the generation of color aberration by the difference of the wavelengths of the light beams 4 and 5 and the light is excellently converged on the respective information recording surfaces 2a and 3a even when the thickness of the transparent substrate is different. <P>COPYRIGHT: (C)2004,JPO |
