PURPOSE: To apply desired attenuation characteristics to an optical fiber cable with a casing by providing the casing made of polymer materials for the optical fiber and setting a desired value within a limited temperature range for the thermal expansion coefficient of this casing.

CONSTITUTION: Within a limited temperature detection range T1-T2, a thermal expansion coefficient -α0 provided for the polymer materials is made different from the thermal expansion coefficient of the same materials within adjacent temperature ranges T0-T1 and T2-T3, and the level of a thermal expansion coefficient α within the adjacent temperature ranges is reduced in comparison with the thermal expansion coefficient within the temperature detection range. Then, when a clad 12 is affected from a polymer casing 14, according to the composition of polymer materials, an optical pulse P is attenuated within the range from 0.01db to 0.1db at the interval of 1m of the fiber cable. Thus, desired attenuation characteristics are applied to the optical fiber cable.