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Investigation of fiber Bragg gratings for high-power multi-mode XLMA-based fiber lasers

: Klein, S.; Fitzau, O.; Giesberts, M.; Traub, M.; Hoffmann, H.D.; Krause, V.; Rehmann, G.


Carter, A.L. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Fiber Lasers XVI: Technology and Systems : 4-7 February 2019, San Francisco, California, United States
Bellingham, WA: SPIE, 2019 (Proceedings of SPIE 10897)
ISBN: 978-1-5106-2437-5
ISBN: 978-1-5106-2436-8
Art. 1089713, 8 pp.
Conference "Fiber Lasers - Technology and Systems <16, 2019, San Francisco/Calif.>
Industrial Laser, Laser Source and Laser Applications Conference (LASE) <2019, San Francisco/Calif.>
Photonics West Conference <2019, San Francisco/Calif.>
Conference Paper
Fraunhofer ILT ()

Within the EKOLAS consortium, which is part of the BmBF-funded Effilas (Efficient high-performance laser beam sources) research alliance, we are developing Fiber Bragg Gratings (FBGs) written in extra-large mode area (XLMA) fibers. By using FBGs as fiber integrated output mirrors, which is state-of-the-art in single-mode fiber lasers, we aim to reduce complexity and increase robustness and reliability of multi-mode fiber resonators. To this end, we are investigating the use of FBGs as outcoupling mirrors with a reflectivity below 10 % in XLMA high-power multi-mode fiber lasers. As a first step, FBGs are written into a passive 105/125 μm multi-mode fiber. We present their application for frequency stabilization of a resonator based on XLMA fibers, and tested the FBGs up to an output power of 150 W at 1075 nm without failure. As the next step, transition from passive 105/125 μm fibers to active XLMA fibers is currently being investigated. For FBG inscription, we use a phase mask and an ultra-fast laser system (100 fs, 800 nm). The setup is adjustable in three translation and three rotation axes. Additionally it features a modular mechanical design for fast and flexible interchanging of fiber mounts, phase mask and process optics. The FBGs are pre-characterized in transmission with a white-light source and an optical spectrum analyzer.