Simultaneous Dual-Domain Sensing Based on Forward-Stimulated Brillouin Scattering in Cascaded Optical Fibers

In this work, we use the fiber Sagnac loop to demodulate forward-stimulated Brillouin scattering (FSBS) in cascaded optical fibers of single mode fiber (SMF) and high nonlinear fiber (HNLF) and demonstrate a dual-domain, dual-parameter simultaneous sensing system. Due to the differences in fiber diameter and type, the FSBS spectrum can reflect and distinguish the gain peaks of SMF and HNLF which are located in separate sensing regions. Since the transverse acoustic waves (TAWs) make response to acoustic properties and mechanical changes outside the optical fiber and then affect the modulation effect of the TAWs on light waves, simultaneous sensing of regional temperature and acoustic impedance in another region is realized by analyzing the center frequency shifts or linewidth changes of appropriate gain peaks in FSBS spectrum. The highest temperature and acoustic impedance sensitivities achieved were 49.536 kHz/°C and 4.285 MHz/[kg/(s $\cdot $ mm2)], and the highest accuracies were 0.15 °C and 0.019 [kg/(s $\cdot $ mm2)], respectively, which are both at the desired level. We believe that this sensing system provides an efficient and novel idea for multi-domain and multiparametric measurement applications, such as energy monitoring, environmental detection, engineering or instrumentation monitoring, and biomedical fields.