Localization of a loss-inducing perturbation for a fiber optic alarm-condition sensor using an un-modulated light source

We present a new method for localization of a loss region for a distributed fiber optic alarm condition sensor based on transmission/reflection analysis. We have demonstrated that the proposed sensor, based on Rayleigh scattering, allows for the localization of one loss-inducing perturbation along a sensing fiber by measuring only transmitted and Rayleigh backscattered powers of unmodulated CW (continuous wave) light. Localization of a strong disturbance with an accuracy of 1 m close to the source-end and 5 m close to the output-end of a 4.04 km long single-mode sensing fiber was demonstrated. We believe the proposed technique should be very attractive for the eventual realization of a compact and inexpensive distributed alarm fiber optic sensor.