Alarm-condition detection and localization using Rayleigh scattering for a fiber-optic bending sensor with an unmodulated light source

We present a simple method for the localization of a bending loss region for a fiber-optic alarm-condition sensor based on the measurement of transmitted and Rayleigh backscattered power. Bending the sensing fiber affects both the transmitted and backscattered power of unmodulated continuous-wave (CW) light that is launched into the fiber. The position of the loss region is determined from unique relationships between normalized transmitted and backscattered powers for different locations of the disturbance along the fiber. The localization of a strong disturbance with an accuracy of 1 m at positions near the source-end and of 5 in at positions near the remote-end of a 4.04 km length singlemode fiber was demonstrated. (C) 2002 Elsevier Science B.V. All rights reserved.