LENS AND OPTICAL SYSTEM USING THE SAME, OPTICAL HEAD AND OPTICAL DISK DEVICE

摘要

PROBLEM TO BE SOLVED: To condense a light beam with high light utilization efficiency to a plurality of kinds of optical recording media varying in the thicknesses of transparent substrates respectively.

SOLUTION: When the optical disk device is loaded with a DVD of 0.6 mm in thickness t1of a DVD substrate 2, the light beam 4 of a wavelength λ1=655 nm is used as a luminous flux of a numerical aperture NA=0.60 and is condensed to the information recording surface 2 of the DVD substrate 2. When the optical disk device is loaded with a CD of 1.2 mm in thickness t2of a CD substrate 3, the light beam 5 of a wavelength λ2=790 nm is used as a luminous flux of a numerical aperture nearly 0.45 and is condensed to the information recording surface 3a of the CD substrate 3. The wavefront aberration by a difference in the thicknesses between the substrates 2 and 3 of the DVD and the CD is generated but is offset by the occurrence of the chromatic aberration by a difference in the wavelengths between the light beams 4 and 5. The light beams can thus be well condensed to the respective information recording surfaces 2a and 3a even if there is a difference in the thicknesses of the transparent substrates.

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