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

分布式光学传感器可用于智能城市和农村地区的基础设施监控。它们用于高速公路、铁路系统、管道、建筑物、桥梁等机械应变和温度的分布式传感。高速公路沿线的温度传感器可以用来发出结冰警告，还可以检测到管道中的泄漏。通过在桥梁、水坝或建筑物中进行应变传感，可以控制机械结构，并可以立即发现缺陷，以防止例如灾害。对于分布式传感，可以考虑拉曼散射或布里渊散射的非线性效应。然而，与拉曼传感器相比，分布式布里渊传感器具有许多优点。布里渊传感器的空间分辨率在厘米范围内，与光纤布拉格光栅等点传感器相当。然而，布里渊传感器在远距离上提供了完全连续的传感，相当于数千个不同点传感器，不需要特殊的光纤制备。因此，为了更加安全和有效地预防与自然威胁（山体滑坡、地震、雪崩、洪水等）和现代建筑（隧道、铁路、管道、桥梁等）有关的危险，分布式传感器有望在发达社会中产生非常重要的经济影响[Luc11]。因此，在过去的几年中，SBS传感器的研究活动非常活跃。然而，布里渊传感器的传感机制取决于由两个光波相互作用产生的声波的频率和寿命。它的频率是温度和应变的量度，而声子寿命定义了空间分辨率。到目前为止，所有的布里渊传感器都只使用其中一种声波进行传感。因此，这些传感器的最大传感长度和空间分辨率受到限制。本课题的目的是通过对受激布里渊散射的增益谱进行工程设计，以显著改善分布式温度和应变传感器。

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.