PURPOSE: To greatly improve the change rate of backward scattered light and to improve temp. sensitivity by forming the core of an optical fiber of glass layers which are different in coefft. of thermal expansion and are formed in multiple layers.
CONSTITUTION: The core 5 having the refractive index higher than the refractive index of a clad 4 of the optical fiber is formed on the inside of the clad. The core 5 is made into the multiple-layered structure in which glass layers 8 having the large coefft. of thermal expansion and glass layers 7 having the small coefft. of thermal expansion are alternately formed in ≥10 layers to a coaxial cylindrical shape. The core which is multiple-layered in such a manner is so constituted that the dopant concn. of the glass layers 7, 8 are higher nearer the central part of the core to constitute the optical fiber having the refractive index distribution 6 larger the nearer the central part of the core. The glass layer 7 having the small coefft. of thermal expansion is formed by incorporating the GeO2 dopant into SiO2 and the glass layer 8 having the large coefft. of thermal expansion is formed by incorporating the F dopant, etc., into GeO2. The change rate of the backward scattered light with the temp. change is thereby greatly improved and the temp. sensor having the high sensitivity and high accuracy is obtd.
TSUCHIYA SHINICHI
TSUTSUI TERUAKI
YAMAMOTO SATORU
HITACHI CABLE