Abstract: In order to supply the optical fiber for attenuating optical signal enable the attenuation amount to become flat in wide wavelength scope, simultaneously adding at least two kinds of dopants for attenuating optical signal over the core and the cladding of the optical fiber. Then, properly adjusting the kind and the concentration of dopants for manufacturing the optical fiber 1 for attenuating optical signal; simultaneously adding the dopant enabling the absorption of optical signal to increase with the wavelength become long and the dopant enabling the absorption of optical signal to decrease with the wavelength become long. As the dopant, it is desired to select at least two kinds of transitional metals from Co, Ni, Cr, V, Fe, Mn, Tb and Tm. Further, as the doped area, it is desired to dope the 6 times of the center portion of the core from the center of the core.

Abstract: In order to supply the optical fiber for attenuating optical signal enable the attenuation amount to become flat in wide wavelength scope, simultaneously adding at least two kinds of dopants for attenuating optical signal over the core and the cladding of the optical fiber. Then, properly adjusting the kind and the concentration of dopants for manufacturing the optical fiber 1 for attenuating optical signal; simultaneously adding the dopant enabling the absorption of optical signal to increase with the wavelength become long and the dopant enabling the absorption of optical signal to decrease with the wavelength become long. As the dopant, it is desired to select at least two kinds of transitional metals from Co, Ni, Cr, V, Fe, Mn, Tb and Tm. Further, as the doped area, it is desired to dope the 6 times of the center portion of the core from the center of the core.