Wavelength-scanning coherent OTDR for dynamic high strain resolution sensing

Distributed vibration sensing in optical fibers opened entirely new opportunities and penetrated various sectors from security to seismic monitoring. Here we demonstrate a most simple and robust approach for dynamic strain measurement using wavelength-scanning coherent optical time domain reflectometty (C-OTDR). Our method is based on laser current modulation and Rayleigh backscatter shift correlation. As opposed to common single wavelength phase demodulation techniques, also the algebraic sign of the strain change is retrieved. This is crucial for the intended applications in structural health monitoring and modal analysis. A linear strain response down to 47.5 p epsilon and strain noise of 100 p epsilon/root Hz is demonstrated for repetition rates in the kHz range. A field application of a vibrating bridge is presented. Our approach provides a cost-effective high-resolution method for structural vibration analysis and geophysical applications. (C) 2018 Optical Society or America under the terms Idle OSA Open access Publishing Agreement