Abstract

A method to evaluate distributed temperature gradients along an optical fiber using phase-sensitive optical time domain reflectometry (Phi OTDR) with direct detection is proposed and experimentally validated. The measurement principle derives from the perturbation response of a single-wavelength Phi OTDR signal, which is analyzed as a unidimensional speckle pattern. Our method can be implemented in real-time, relies solely on a low-cost post-processing of the standard Phi OTDR traces and requires no scanning of the laser frequency. This post-processing method can be implemented over a conventional Phi OTDR system used for distributed intrusion detection, without affecting its operation or requiring any additional hardware.