PURPOSE: To surely detect abnormality occurrence and its position by detecting the occurrence of loss increase and the position optically since the optical fiber core inside a protective layer is bent at a small radius of curvature, being pressed against a projection and receiving side pressure when it receives external pressure therefore the increase of the transmission loss of the optical fiber occurs at that position.
CONSTITUTION: This sensor is equipped with an interposition 25 provided with a groove, which has a spiral groove 27 at the periphery, an optical fiber core 29, which is accommodated in the groove 27, and a protective layer 31, which covers the interposition 25 provided with a groove 25. A projection 33 is made at the bottom of the groove 27, and the depth H of the groove and the outside diameter D of the fiber core are in such relation that the optical fiber 29 is pressed against the projection 33 when external pressure is applied to the protective layer 31.
MATSUOKA RYUICHI
SUZUKI KATSUAKI
TAKASE ATSUO
