Abstract
The distributed fibre sensing technology based on backward stimulated Brillouin scattering (BSBS) is experiencing a rapid development. However, all reported implementations of distributed Brillouin fibre sensors until today are restricted to detecting physical parameters inside the fibre core. On the contrary, forward stimulated Brillouin scattering (FSBS), due to its resonating transverse acoustic waves, is being studied recently to facilitate innovative detections in the fibre surroundings, opening sensing domains that are impossible with BSBS. Nevertheless, due to the co-propagating behaviour of the pump and scattered lights, it is a challenge to position-resolve FSBS information along a fibre. Here we show a distributed FSBS analysis based on recovering the FSBS induced phase change of the propagating light waves. A spatial resolution of 15 m is achieved over a length of 730 m and the local acoustic impedances of water and ethanol in a 30 m-long uncoated fibre segment are measured, agreeing well with the standard values.
Highlights
The distributed fibre sensing technology based on backward stimulated Brillouin scattering (BSBS) is experiencing a rapid development
We demonstrate a technique to measure the distributed forward stimulated Brillouin scattering (FSBS) spectrum and retrieve the local acoustic impedance of the surrounding materials
The acoustic impedances of water and ethanol obtained by this technique agree well with the reported standard values
Summary
The distributed fibre sensing technology based on backward stimulated Brillouin scattering (BSBS) is experiencing a rapid development. Considering the narrow resonance linewidth and large frequency-detuning features of the BSBS process, the intensity evolution of several reading pulse sidebands are independently selected and measured as a function of distance over a sensing fibre; this particular step is similar to Brillouin optical time-domain analysis (BOTDA)[1,2]. Both transversal and longitudinal acoustic waves (activated by FSBS and BSBS, respectively) are independently and distinctively used in our technique without cross-interaction. The demonstrated distributed FSBS analysis is not limited to sensing applications, and aiming at verifying positiondependent FSBS theoretical models[18] and characterising local FSBS in a waveguide, which are as well within the scope of this analysis technique
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