| 摘要 |
PROBLEM TO BE SOLVED: To provide a detector with a detection signal on movable body displacement clearly expressed without being buried in noises. SOLUTION: An optical fiber sensor 6 is connected to branch optical fibers 5a severally branched, via couplers 4, from an optical fiber line 1 at a plurality of positions, the fiber sensor 6 comprising a sensor part 5c given bending deformation, for example, by opening/closing a lid 3 of a manhole. An FBG (fiber Bragg grating) 7 as a reflection part is provided on a front end of the sensor part 5c given the bending deformation. When letting pulse light into the fiber line 1, it is detected by OTDR 9 that the level of light reflected/returned by the FBG 7 varies owing to a decrease in the amount of light caused by light loss at the sensor part 5c, thereby detecting the displacement of each lid 3. Since the level of a reflection peak produced by being reflected by the FBG is remarkably high as compared with noise levels, it can be surely detected without being drowned out by noises. The width of a pulse can be narrowed down, allowing respective optical fiber sensors to perform detection separately with reflection kept from overlapping even if the sensors are placed close to each other. COPYRIGHT: (C)2006,JPO&NCIPI |
