| 摘要 |
PURPOSE: An object lens of a numerical aperture(NA) mounted to an optical head of an optical device records/reproduces various kinds of optical of disks. CONSTITUTION: An objective lens(10) of optical disk includes a refractive lens having a positive diffraction power, and a diffraction lens structure having a plurality of concentric ring-type steps formed on a lens surface of the refractive lens. The refractive lens structure has a wavelength dependence characteristic. At least two beams having a different wavelength of the same degree forms a proper fracture about at least two optical disks having cover layer of a different thickness. Thereby, by reducing a driving portion of the objective lens, a compact device and a high-speed operation device are made.
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