Experimental study on depolarized GAWBS spectrum for optomechanical sensing of liquids outside standard fibers.

We report an experimental study on the spectral dependence of depolarized guided acoustic-wave Brillouin scattering (GAWBS) in a silica single-mode fiber (SMF) on acoustic impedance of external materials. The GAWBS spectrum was measured when the acoustic impedance was changed from 1.51 to 2.00 kg/s·mm². With increasing acoustic impedance, the linewidth increased; the dependence was almost linear with an acoustic impedance dependence coefficient of 0.16 MHz/kg/s·mm². Meanwhile, with increasing acoustic impedance, the central frequency linearly decreased with an acoustic impedance dependence coefficient of -0.07 MHz/kg/s·mm². These characteristics are potentially applicable to acoustic impedance sensing.