Final Report Summary - U-FINE (Ubiquitous optical FIbre NErves) Distributed optical fibre sensors (DOFS) are a unique class of photonic sensors in which an optical fibre cable acts as the sensing element and a quantitative measure can be performed at any position along the fibre, making possible long-range continuous measurements over tens of kilometers. This way a conventional optical fibre may substitute for many thousands of point sensors and provide a direct map of the quantity to be measured. DOFS have become a widely used tool for critical asset monitoring in civil engineering and energy transport. However, beyond certain specific applications in these domains, little or no application had been found for these sensors. The aim of U-FINE was to develop a new class of multi-scale DOFS systems that would find use in a wide range of new application domains ranging from biomechanics to smart grids. After five years of development, the U-FINE project has substantially contributed to the development of DOFS technology, particularly in the aspects of resolution, range, measurement time, sensitivity and exploration of new applications. The project has also opened up the possibility of using DOFS technology in new domains such as seismology or water transport. With respect to the main performance metrics of these sensors (resolution, range, measurement time, sensitivity, number of measured points), the project has been able to go well beyond the state of the art in all of them. In terms of range, the systems developed in U-FINE have allowed reaching the record of 240 km monitored distance, well beyond the initial expectations when the project started. In terms of dynamic analysis, the project team has been able to reach single-shot true strain/temperature measurements, allowing e.g. to perform distributed monitoring of ultrasound waves over a structure of >1 km. In terms of sensitivity, the U-FINE project has contributed to the development of distributed measurement techniques allowing the detection of sub-nanometric variations in fiber geometry. In terms of e.g. strain sensitivity, the latest measurement schemes developed by the project team have allowed the monitoring of relative deformations with picostrain/sqrt(Hz) sensitivity, something very challenging even for dedicated point sensors. In terms of resolution, the project team has been able to develop distributed sensing schemes with 3mm spatial resolution while still allowing single-shot performance. In terms of number of resolved points, the time-domain systems developed in the project have been able to reach 1,000,000 sensing points, a figure which is considered a landmark in the community (and which triggered substantial interest in the form of press releases and interviews). Overall, the technological achievements of the project can be qualified as extremely interesting. As a benchmark of the interest of the project results, some developments have brought the interest and direct implication of EU industry, who have licensed some of the patents developed by the team along the duration of the project.Some of the progress developed in U-FINE has had an impact on other areas of knowledge such as communications, geology, civil engineering, and security. As an example of this, we can cite the application of the systems developed in U-FINE to the monitoring of a big and largely unknown ecological and geological problem: burning coal waste piles. The U-FINE team has developed a whole new testing methodology for the assessment of these residues, allowing indirect quantification of pollutants and geological changes. U-FINE systems are attractive solutions to monitor this environment thanks to their wide coverage, extremely high resolution and sensitivity and ability to withstand very high temperatures (up to 300 ºC). This new methodology has meant a breakthrough in our knowledge of coal waste piles and their evolution. Another area that can be cited is seismology, with current tests being developed in collaboration with Caltech Seismology Lab.Along the development of the project, the group has consolidated as a world-leader in the field of distributed optical fiber sensors and a major contact point for scientists and technologists in this domain, as evidenced in all the collaborations performed by the group and all the industrial interest driven by the results.
