Discriminative Sensing of Acoustic Impedance and Temperature Based on Spatial-Division Multiplexed Forward Brillouin Scattering in Multicore Fiber

A novel method for discriminative sensing of acoustic impedance and temperature based on space-division multiplexing (SDM) and forward Brillouin scattering (FBS) in multicore fiber (MCF) is proposed and experimentally validated. Besides it is based on different responses of radial acoustic mode ( $\textit{R}_{\text{0},\textit{m}}$ ) and torsional-radial acoustic mode ( ${\textit{TR}}_{\text{2},\textit{m}}$ ) to the acoustic impedance and temperature. The linewidth sensitivity coefficients corresponding to a ${R} _{{0},{m}}$ mode of the central core and the frequency shift sensitivity coefficients corresponding to the TR ${}_{{2},{m}}$ modes of the central and outer cores in a seven-core fiber were measured. The new phenomena are that the frequency shift-acoustic impedance coefficient of the TR ${}_{{2},{m}}$ mode in the outer core is 6.4 times higher than that in the central core. Therefore, we adopted a combination of the ${R} _{{0},{m}}$ mode in the central core and the TR ${}_{{2},{m}}$ mode in the outer core, enabling a discriminative measurement of temperature and acoustic impedance. Particularly, the simultaneous use of the ${R} _{{0},{m}}$ mode in the central core and the TR ${}_{{2},{m}}$ mode in the outer core exhibited a low acoustic impedance measurement error of 0.002 kg $\cdot $ s ${}^{-1} \cdot $ mm ${}^{-{2}}$ and a temperature error of $0.1~^{\circ }$ C. Moreover, the accuracy of measuring acoustic impedance is 3 times higher than that of large effective area fiber (LEAF). The proposed sensor offers significant advantages, including simplicity of fabrication, large transmission capacity, and high measurement accuracy, making it a promising platform for discriminative acoustic impedance sensing applications.