In this paper, we present our current work towards a highly efficient XLMA (extra-large mode area) fiber-based laser, which is being performed in the EKOLAS consortium within the BMBF-funded EffiLAS (efficient high-performance laser beam sources) research alliance. To this end, the complete manufacturing process chain of the XLMA fiber was reviewed and optimized. The work started with the material composition of the active XLMA preform with the goal of improving the purity and thus the background loss. A successfully implemented fluorine co-doping process allows refractive index adjustment of the active core material which improves the beam quality of the laser fibers without changing the concentration of active ions in the glass composition. The preform is subjected to a screening in which possible scatter centers, e.g. bubbles, inclusions or contaminants, are mapped and categorized, in order to identify defects, which could lead to a failure in the drawn fiber, already at an early production stage. The subsequent fiber drawing is monitored for scattering using the emissions from the heated preform as well as for inhomogeneities of the dopants using a phase measurement technique. Finally, the fiber is tested for residual impurities and background losses using a multi-mode OTDR to ensure that the fibers are free of any defects.
The main goal of the presented work was to evolve a multifunctional beam composed out of fiber reinforced plastics
(FRP) and an embedded optical fiber with various fiber Bragg grating sensors (FBG). These beams are developed for the
use as structural member for bridges or industrial applications. It is now possible to realize large scale cross sections, the
embedding is part of a fully automated process and jumpers can be omitted in order to not negatively influence the
laminate. The development includes the smart placement and layout of the optical fibers in the cross section, reliable
strain transfer, and finally the coupling of the embedded fibers after production. Micromechanical tests and analysis were
carried out to evaluate the performance of the sensor.
The work was funded by the German ministry of economics and technology (funding scheme ZIM). Next to the authors
of this contribution, Melanie Book with Röchling Engineering Plastics KG (Haren/Germany) and Katharina Frey with
SAERTEX GmbH & Co. KG (Saerbeck/Germany) were part of the research group.
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