| 摘要 |
The present invention relates to an optical fiber for light pulse expansion in which the ratio (² 3 /² 2 ) of the third derivative ² 3 to the second derivative ² 2 is negative, the absolute value thereof is large, and the absolute value of the second derivative ² 2 is also large. Such an optical fiber comprises at least a central core portion having a maximum refractive index N 1 and an outer diameter 2a, a depressed portion, provided on the outer periphery of the central core portion, having a minimum refractive index N 2 and an outer diameter 2b, and a cladding portion, provided on the outer periphery of the depressed portion, having a maximum refractive index N 3 . The respective maximum refractive indices of the central core portion, the depressed portion and the cladding portion satisfy the relationship "N 1 >N 3 >N 2 ". The relative refractive index difference ” 1 of the central core portion with respect to the cladding portion is larger than 1.0%, and the relative refractive index difference ” 2 of the depressed portion with respect to the cladding portion is smaller than -0.3%. At the wavelength of 1.05 µm, the second derivative ² 2 of the propagation constant ² with respect to frequency É is positive, the third derivative ² 3 of the propagation constant ² with respect to frequency É is negative, and the ratio (² 3 /² 2 ) is -0.002 ps or less.
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