Fabrication and characterization of Bragg gratings in perfluorinated polymer optical fibers and their embedding in composites

Fiber Bragg gratings (FBG) have attracted interest especially in the field of structural health monitoring (SHM) and online process monitoring. The main objectives of this study are an ultraviolet laser based generation of Bragg gratings in a perfluorinated polymer optical fiber (POF) and their optical, thermo-mechanical and mechanical characterization. This kind of polymer fiber has a higher optical transparency than typical polymer fibers based on polymers with carbon hydrogen bonds like polymethylmethacrylate, which is the most used material for polymer optical fibers to date. Until recently only gratings inscribed by the phase mask technique in thin slabs of the amorphous fluoropolymer CYTOP (cyclic transparent optical polymer) made from polymer fibers were successfully detected. Here infrared spectra of Bragg gratings in the core of perfluorinated polymer optical fibers are presented and the embedding of the bare perfluorinated polymer fibers without the over-cladding (reinforcement) layer are described for the first time. The inscription of the gratings in the core of the polymer optical fiber was done using a krypton fluoride excimer laser (248 nm, 5 eV) and the well-known phase mask method. An advantageous mechanical characteristic of the perfluorinated polymer optical fibers compared to glass optical fibers is the failure strain. In structural health monitoring applications, where strains higher than 10% have to be measured, polymer optical fibers are feasible in contrast to glass optical fibers. The results are also promising regarding stability and reliability. This could open a new field of POF sensing of parts, structures and devices.