To provide a fiber for attenuating an optical signal which is easily manufactured and exhibits excellent flatness of wavelength characteristic in a communication wavelength range.
In the fiber for attenuating the optical signal which is formed by adding to a core a dopant for attenuating the optical signal, a virtual temperature at which glass is turned from a melting state to a solid state is decreased to ≤ 1,500°C, particularly preferably ≥ 900°C to ≤1,300°C. The decrease of the virtual temperature is performed by adding a dopant for decreasing the virtual temperature, annealing an optical fiber or controlling a cooling condition in the drawing of the optical fiber. Because the virtual temperature is controlled to ≤ 1,500°C, the attenuation quantity in 1,310 nm and 1,550 nm which are the communication wavelength range is flattened.
NOUCHI KENTARO
YAMAGUCHI MASAMITSU
TANIMOTO HAJIME
MATSUYAMA EIJI
Hiromichi Watanabe