| 摘要 |
<P>PROBLEM TO BE SOLVED: To enable a light beam to be condensed on information recording surfaces of a variety of optical recording media having different transparent substrate thicknesses with a high optical utilization efficiency. <P>SOLUTION: When an optical disk device is loaded with a DVD whose a thickness t<SB>1</SB>of a DVD substrate 2 is 0.6 mm, a light beam 4 with a wavelength λ<SB>1</SB>of 655 nm is used as a beam with numerical aperture NA of 0.63 to be condensed on an information recording surface 2a of the DVD substrate 2. Moreover, when the optical disk device is loaded with a CD whose the thickness t<SB>2</SB>of a CD substrate 3 is 1.2 mm, a light beam 5 with a wavelength λ<SB>2</SB>of 790 nm is effectively used as a beam with a numerical aperture of about 0.45 to be condensed on an information recording surface 3a of the CD substrate 3. Although the wave aberration due to the different thicknesses of the substrates 2, 3 of the DVD and the CD occurs, this is offset by the occurrence of the chromatic aberration due to the different wavelengths of light beams 4, 5. Even when a difference is in the thickness of a transparent substrate, condensing is performed excellently on respective information recording surfaces 2a, 3a. <P>COPYRIGHT: (C)2004,JPO |
