Highly-sensitive distributed dynamic strain sensing via perfect periodic coherent codes

Distributed dynamic strain sensing is of interest in applications such as structural health monitoring, shape sensing and more. Achieving high spatial resolution along with high sensitivity, fast update rate and long range is a challenging task. A potential approach for improving the performance of distributed strain sensors is via coding. Despite its great success in Stimulated Brillouin Scattering based sensors and the significant attention it drew in the context of static reflectometry, its application for Rayleigh Scattering based dynamic strain sensing was rarely studied. In this work, a biphase Legendre sequence with near perfect periodic autocorrelation was used for significantly enhancing the performance of a coherent φ-OTDR DAS system. The new method experimentally detected 175Hz sinusoidal dynamic strain of amplitude ~ 2nε . The spatial resolution was 14.7cm, the range was 1km and the noise level corresponded to sensitivity of ~ 70 pε √.