Quasi-single mode operated few-mode fiber for distributed acoustic sensing

We experimentally report a proof-of-concept demonstration of a few-mode fiber (FMF) based distributed acoustic sensor (DAS) design, aiming at upgrading the capabilities of the typical DAS that employs the standard single mode fiber (SMF). We only excite the fundamental mode at the input port of the FMF, and further, we minimize the impact of intermodal coupling within it such that the FMF operates in a quasi-single mode (QSM) state. The QSM operated FMF keeps the basic operation principle of the DAS valid and, in comparison with the standard SMF, it allows injection of higher pump peak-power before reaching the threshold power of nonlinearity. We validate our design by sensing vibration events produced by a piezoelectric transducer (PZT) cylinder. The FMF based DAS successfully figures out the locations and frequencies of these events. This reported design would enable the realization of a DAS design with longer sensing range and higher spatial resolution, in comparison to the standard SMF based DAS.