| 摘要 |
Optical fibers to form an optical transmission line suitable for WDM transmission in a wide-spreading wavelength band, having the following characteristics and parameters: a dispersion in absolute value of 0.5 ps/nm/km to 9 ps/nm/km in a wavelength band of 1430 nm to 1625 nm, a dispersion slope in absolute value of 0.04 ps/nm<SUP>2</SUP>/km or less at a wavelength of 1550 nm, a mode field diameter of 7 mum or less at a wavelength of 1550 nm and a cable cutoff wavelength of less than 1430 nm; core 11 surrounded by cladding 7 , core 11 being at least two-layered (first layer 1 at the center and second layer 2 surrounding the first layer; relative refractive index of glass layer Delta 1 with reference to the cladding being adjusted to not less than 0.6 but not more than 1.6%, relative refractive index of second layer Delta 2 with reference to the cladding being adjusted to a negative value.
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