The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Dec. 28, 2004
Filed:
Sep. 26, 2003
Yasuyuki Sugi, Naka-gun, JP;
Takesuke Maruyama, Yokohama, JP;
Hitachi Maxell, Ltd., Ibaraki, JP;
Abstract
When the DVD provided with the DVD substrate having thickness t of 0.6 mm is installed in the optical disc apparatus, the light beam having wavelength &lgr; =655 nm is used as luminous flux of numerical aperture NA=0.63 to be condensed on the information surface on the DVD substrate . When the CD provided with the CD substrate having thickness t of 1.2 mm is installed in the optical disc apparatus, the light beam having wavelength &lgr; =790 nm is effectively used as luminous flux of approximate numerical aperture NA=0.45 to be condensed on the information surface on the DVD substrate . The wavefront aberration caused by a thickness difference between the DVD substrate and CD substrate is canceled out by the chromatic aberration caused by a wavelength difference between the light beams and . Therefore, in spite of the difference in the transparent substrates, the light beams are suitably condensed respectively on the information surface and