Distributed Brillouin Fibre Sensing

An important field of research in our Group is Distributed Brillouin Optical Fibre Sensing. Brillouin scattering accounts for one of the light-scattering mechanisms harnessed in optical fibres to realise distributed sensing. It originates from the interaction of light with density fluctuations induced by the propagation of acoustic waves in the fibre. The elevated optical intensity resulting from the tight confinement of light in optical fibres combined to ultra-low propagation loss make this type of waveguide propitious to the triggering of Brillouin scattering even at moderate optical power. Since the interaction involves acoustic waves, its signature depends on the mechanical properties of the fibre. This feature has been judiciously exploited to measure, among other physical quantities, temperature and strain in a distributed flavour.

Most Brillouin based sensors operate by launching an optical pulse into an optical fibre and analysing the light backscattered from the opto-acoustic interaction. By measuring the temporal evolution of the returning signal, a mapping of the Brillouin interaction along the fibre can be performed. A time of flight measurement enables a precise localisation of any event occurring along the fiber, such as e.g. a sudden temperature change.

Figure 1: Schematic showing the propagation of the input pulse, the acoustic waves generated due to Brillouin scattering, and the back-reflected light.

Current research on Brillouin distributed sensors involve refinements of the existing setups by employing sophisticated optical techniques such as for example optical pulse coding, where several pulses are present simultaneously in the fibre, which improves the system response but requires appropriate decoding of the measured signal. Other advanced topics include exploiting different acoustic modes to probe parameters to which conventional systems remain insensitive.

Figure 2: Schematic showing acoustic modes in an optical fibre.
For more information:
  • Chow, D. M., Yang, Z., Soto, M. A., & Thévenaz, L. (2018). Distributed forward Brillouin sensor based on local light phase recovery. Nature communications, 9(1), 2990.

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  • Yang, Z., Li, Z., Zaslawski, S., Thévenaz, L., & Soto, M. A. (2018). Design rules for optimizing unipolar coded Brillouin optical time-domain analyzers. Optics express, 26(13), 16505-16523.

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