| 摘要 |
<P>PROBLEM TO BE SOLVED: To converge an optical beam on an information recording surface with high efficiency of using light for each of plural kinds of optical recording media that differ in the thickness of their transparent substrates. <P>SOLUTION: When a DVD having a DVD substrate 2 of a thickness t<SB>1</SB>of 0.6 mm is loaded in an optical disk device, the optical beam of a wavelength λ<SB>1</SB>of 655 nm is used as the luminous flux of numerical aperture NA of 0.63 and is made to converge on the information recording surface 2a of the DVD substrate 2. When a CD, having a CD substrate 3 of a thickness t<SB>2</SB>of 1.2 mm, is loaded in the optical disk device, an optical beam 5 of a wavelength λ<SB>2</SB>of 790 nm is used effectively as luminous flux of a numerical aperture of substantially 0.45 and is converged on the information recording surface 3a of the CD substrate 3. Wave front aberrations occur due to the difference in the thickness between the substrates 2 and 3 of the DVD and CD, however, the wave front aberrations are canceled by chromatic aberrations due to the wavelength difference between the optical beams 4 and 5. Thus, even if there are thickness differences between the transparent substrates, optical beams are made to converge properly on the information recording surfaces 2a and 3a. <P>COPYRIGHT: (C)2007,JPO&INPIT |
