The attenuation properties of Co2+-doped single-mode optical fibers were ex
perimentally and analytically investigated for preparation of a stable flat
band attenuator. By controlling the Co2+-doped region in a fiber core, we c
ould prepare a flatband attenuator in which the attenuation in wavelengths
1530-1610 nm was held to within 9.9-10.2 dB (3% variation) and the fluctuat
ion of attenuation was less than 0.1 dB with 1-W input power for 100 h. (C)
2001 Optical Society of America.