Principle and recent progress in distributed optical fibre sensing

Using the most advanced optical interactions, optical fibres open the possibility to realise distributed sensing, which means that each point along the fibre can separately and selectively sense quantities, in total similarity to a real organic nerve. The fibre can therefore distinctively inform on the position of the stimulus and on its magnitude and up to 1 million points can be separately and independently addressed anywhere along the fibre. The demand on distributed fibre sensors has been increasing over the past years in many application fields due to their unique capability to monitor environmental quantities such as strain and temperature changes over many tens of kilometres of optical fibres with metric spatial resolution, bringing a response to a societal concern for a safer natural and human environment.
To date, the identified suitable interactions that are used in distributed sensing are the three optical scatterings observed in silica: the elastic Rayleigh scattering and the two non-elastic Brillouin and Raman scatterings. While Raman scattering provides a reliable method to measure temperature only, Brillouin and Rayleigh scatterings are temperature and strain dependent processes. We shall review the physical principles behind the sensing process and the main types of distributed sensors, illustrated by several examples, and we shall show the latest developments in this promising field.