Single-Shot COTDR Using Sub-Chirped-Pulse Extraction Algorithm for Distributed Strain Sensing

Distributed optical fiber sensing, which uses telecom fiber as sensing medium, can realize high-precision temperature/strain monitoring along the fiber, making it an indispensable tool for structural health monitoring, security monitoring, seismic wave detection, etc. In this article, for the first time, a novel sub-chirped-pulse extraction algorithm (SPEA) is proposed to replace the time-consuming sweeping process in conventional COTDR, and a single-shot coherent optical time domain reflectometry (SS-COTDR) for dynamic strain sensing is demonstrated with very high performance. In order to quantitatively evaluate the maximum measurand change that can be measured per unit time, the measurement slew rate (SR) as an important parameter of COTDR has been analyzed in phase-demodultion scheme and in our scheme. As the proof-of-concept experiments, ultra-high strain sensitivities 2.3 pε/ √Hz is demonstrated in 134 m fiber with 2 m spatial resolution. Without distributed amplification, highperformance distributed strain measurements are demonstrated on 75 km fiber with strain sensitivity better than 100 pε/ √Hz. In addition, this scheme is inherently immune to interference fading, which is disadvantageous for phase demodulation scheme.