Engineering the properties of nonlinear optical effects for the improvement of distributed fiber sensors

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Distributed optical sensors can be used for the monitoring of the infrastructure in smart cities and in rural areas. They are used for the distributed sensing of mechanical strain and temperature along motorways, railway-systems, pipelines, buildings, bridges and so on. The temperature sensing along motorways can be exploited to generate ice warnings and in pipelines leaks can be detected. By strain sensing in bridges, dams or buildings the mechanical structure can be controlled and defects can be detected immediately in order to prevent disasters for instance.For the distributed sensing the nonlinear effect of Raman or Brillouin scattering can be incorporated. However, distributed Brillouin sensors offer many advantages compared to Raman sensors. Brillouin sensors can have spatial resolutions in the centimetre range which is comparable to point sensors like fiber Bragg gratings. However, Brillouin sensors offer a fully continuous sensing over large distances, equivalent to many thousands of distinct point sensors and no special fiber preparation is required. Thus, for more safety and the efficient prevention of dangers related to natural threats (landslides, earthquakes, avalanches, floods, etc.) and to modern constructions (tunnels, railways, pipelines, bridges, etc.) distributed sensors are expected to have a very important economic impact in developed societies [Luc11]. Thus, over the last few years a strong research activity on SBS sensors has been seen. However, the sensing mechanism in Brillouin sensors depends on the frequency and lifetime of an acoustical wave, generated by the interaction between two optical waves. Its frequency is a measure for temperature and strain, whereas the phonon lifetime defines the spatial resolution. All Brillouin sensors up to now use just one of these acoustical waves for sensing. Thus, the maximum sensing length and the spatial resolution of these sensors is restricted. The aim of this project is to significantly improve distributed temperature and strain sensors by the engineering of the gain spectrum of stimulated Brillouin scattering.