Patent ID: 7092610

Claim:
An optical fiber for attenuating an optical signal comprising a core and a cladding, wherein n (n≧2) kinds of dopants are included in the optical fiber for attenuating the optical signal, wherein the concentration Wj (j=1, 2, 3, . . . , n) in weight % is adjusted, with respect to a wavelength λi (i=1, 2, . . . , m; m≧2), to satisfy the following expressions 1 and 2; ⁢ 0.9 < α ⁡ ( λ i ) α ⁡ ( λ k ) < 1.1 ⁢ Expression ⁢ ⁢ 1 α ⁡ ( λ i ) = ∑ j = 1 n ⁢ W j ⁢ A j ⁡ ( λ i ) ⁢ ⁢ Expression ⁢ ⁢ 2 wherein λi is a wavelength of the optical signal, α(λi) is an attenuation amount of the optical fiber for attenuating the optical signal with respect to the optical signal having the wavelength λi, K is a positive integral number, (K=1, 2, . . . , m) and (k≠i), Wj is a concentration of dopant j, and Aj(λi) is an attenuation of the optical fiber for attenuating the optical signal with respect to the optical signal with wavelength λi and the attenuation Ai(λi) is produced by the dopant j of one unit.