Low-frequency line shapes in guided acoustic-wave Brillouin scattering

Abstract

Guided acoustic-wave Brillouin scattering (GAWBS) measurements were performed on 20-cm lengths of optical fibers with particular attention focused on the lowest lying resonance. In 125-μm-diam silica fibers, this resonance was observed to occur at ∼22 MHz and have a line shape which varied erratically from sample to sample. Significant line shape fluctuations were evident even between sequential samples from the same fiber spool. We speculate that the observed effects are attributable to 0.01–0.1 μm distributed geometric deviations from a perfect cylinder.

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

“…The central frequency is known to depend on strain and temperature with dependence coefficients (m = 5) of 1.9 MHz/% and 11 kHz/K, respectively [20,21]. Meanwhile, the spectral linewidth ∆ GB can be estimated by [23]:…”

“…where β is the acoustic loss, which includes the propagation loss in the optical fiber and the reflection loss at the boundary between the cladding and the external material [2,23].…”

Observation of depolarized guided acoustic-wave Brillouin scattering in partially uncoated optical fibers

“…This value includes not only the propagation loss in the optical fiber but also the reflection loss at the boundary between the external material and the cladding. 1,12) The linewidth can change with the external acoustic impedance. The coefficient was measured to be 0.16 MHz=kg=(s•mm 2 ) in the acoustic impedance range of 1.51 to 2.00 kg=(s•mm 2 ) using the fifth acoustic resonance peak.…”