High-sensitivity acoustic impedance sensing based on forward Brillouin scattering in a highly nonlinear fiber.

By using radial acoustic modes induced forward Brillouin scattering (FBS) in a highly nonlinear fiber (HNLF), to the best of our knowledge we have demonstrated acoustic impedance sensing with the sensitivity reaching beyond 3MHz for the first time. Benefiting from the high acousto-optical coupling efficiency, both radial acoustic modes (R) and torsional-radial acoustic modes (TR) induced FBS in HNLF have larger gain coefficient and scattering efficiency than those in standard single-mode fiber (SSMF). This provides better signal-to-noise ratio (SNR) and hence larger measurement sensitivity. By using R mode in HNLF, we have achieved a higher sensitivity of 3.83 MHz/[kg/(s · mm)], in contrast to that of 2.70 MHz/[kg/(s · mm)] when measured using R mode (with almost the largest gain coefficient) in SSMF. Meanwhile, with the use of the TR mode in HNLF, the sensitivity is measured to be 0.24 MHz/[kg/(s · mm)], which is still 1.5 times larger than that reported when using the same mode in SSMF. The improved sensitivity would make the detection of the external environment by FBS based sensors more accurate.