Characterization of FSBS Radial Acoustic Modes in Short Optical Fibers With an All-Fiber Ring Resonator

A highly efficient approach for the interrogation of mechanical vibrations excited by forward-stimulated Brillouin scattering in optical fibers is reported. The method is based on an all-fiber ring resonator. The section of optical fiber in which the FSBS takes place is inserted into the loop. Mechanical oscillations modulate the phase of the light propagating through the fiber loop, resulting in the modulation of the ring transmittance. The method takes advantage of the resonant character of the ring transfer function. It has a very high sensitivity and allows the interrogation of mechanical oscillations excited by FSBS in very short fiber sections. Sub-centimeter recognition is demonstrated in this work. Differences between co- and contra-propagating pump and probe signals are investigated.