| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to detect the leakage of a liq. such as C fuel oil and to constitute an inexpensive structure. SOLUTION: By using the optical fiber sensor constituted by being provided with a bent part 2, in which light propagated into a core at one or several places on the mid-way in the longitudinal direction of the optical fiber 1 coated with a resin, can interfere with a leakage reflected light, which leaks out of the core into a clad layer and is reflected at the interface between the clad layer and a resin covered layer 4 on the outside thereof, and/or a leakage reflected light, which leaks out of the core into the covered resin layer via the clad layer and is reflected at the interface between the resin covered layer 4 and the outside thereof, and by detecting the change of the interference conditions accompanying the change of the refractive index of a medium outside the resin covered layer 4 and/or the change of the interference conditions accompanying the change of the refractive index of the resin covered layer 4 absorbing the medium outside the resin covered layer 4 as the intensity change of light propagated to the core or the change of a spectrum, the change of physical state outside the clad layer is detected.
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