We experimentally report a normalized differential signal processing technique to improve the signal-to-noise ratio (SNR) of a fiber optic distributed acoustic sensor (DAS), in the time-domain. The introduced method is calibrated through comparing it with the typical differential method when using a noisy DAS system that includes a relatively wide linewidth laser. For this system, the normalized differential method allows measuring the vibration locations, produced by a piezoelectric transducer (PZT) cylinder, with enhanced SNR.
Stimulated Brillouin scattering (SBS) based distributed optical fiber sensors have been deployed in a myriad of potential applications. Recently, the characteristics of SBS in few-mode-fibers (FMFs) have been investigated for designing optical sensors of high selectivity. For example, monitoring SBS of the individual modes in a two-mode fiber (TMF) allows simultaneous sensing of temperature and strain. In optical communications, on contrary, SBS degrades the signal-to-noise ratio (SNR) and limits the channel capacity. We here experimentally measure the threshold power required to stimulate Brillouin scattering in an FMF when using different mode-pair combinations as pump and probe signals. In particular, we use mode-division-multiplexing (MDM) to launch different linearly-polarized (LP) modes into the both ends of a TMF. For each mode-pair, we gradually raise the pump power until observing the transition from spontaneous to stimulated Brillouin scattering. The results presented here are considerably important for designing efficient FMF-based optical communications/sensing system.