| 摘要 |
PURPOSE:To make it possible to detect application of external force on an optical fiber without increase in loss by inputting polarized optical pulses into the optical fiber, and measuring the change in polarizing state of backward scattering light from each part of the optical fiber in the longitudinal direction. CONSTITUTION:An optical fiber 180 whose strain distribution is to be measured is collected together by ordinary optical fibers, and an optical fiber cable 17 is formed. Then, a half mirror 16 is used for a directional coupler. Backward scattering light is split in two directions of (y) and (x) which are crossed at a right angle through a polarizing and splitting prism 26. The light beams are received by photodectors 20y and 20x. Then the ratio between the intensities Iy and Ix of the two polarized light beams from the same point of the fiber 180 is obtained, and theta=tan<-1>(Iy/Ix) is computed. The rotation (direction) of the polarizing plane can be detected from the value of phi. Differentiation is performed with phi as the function of a distance. Thus application of a large external force on the optical fiber at a point where the differential coefficient is drastically high can be detected. |
