Thulium-doped fiber performance optimization via fiber bending and twisting and inner-cladding shape design

0555636 - ÚFE 2022 RIV US eng C - Conference Paper (international conference)
Schreiber, Ondřej - Aubrecht, Jan - Jasim, Ali - Todorov, Filip - Honzátko, Pavel
Thulium-doped fiber performance optimization via fiber bending and twisting and inner-cladding shape design.
Proceedings of SPIE. Vol. 11773. BELLINGHAM: SPIE, 2021 - (Kalli, K.), č. článku 117731A. ISBN 978-1-5106-4381-9. ISSN 0277-786X. E-ISSN 1996-756X.
[Conference on Micro-structured and Specialty Optical Fibres VII. Virtual, Online (US), 19.04.2021-23.04.2021]
R&D Projects: GA ČR(CZ) GA19-03141S
Institutional support: RVO:67985882
Keywords : Double-clad active fiber * Pump absorption * Thulium doped fiber laser
OECD category: Optics (including laser optics and quantum optics)
https://doi.org/10.1117/12.2592309

Thulium-doped fiber lasers have been extensively investigated as the most promising source of efficient laser emission at wavelengths around 2 μm, i. e., in the eye-safer spectral region and in the atmospheric window as well. It allows for wide range of applications including medicine, defense, distance measurement or materials processing. To enhance pump absorption efficiency along the active double-clad fiber, good overlap of the pump light and doped fiber core should be achieved along the fiber length. The overlap can be increased by breaking the circular symmetry of the inner cladding by shaping its cross-section. Further mode-mixing and better pump absorption can be achieved by coiling and twisting of double-clad fibers. In this work we present experimental measurement of 792 nm pump cladding absorption of a series of double-clad thulium-doped fibers with respect to their bend radius, the inner cladding cross-sectional shape and twist rate. With these fibers, we assembled a set of fiber lasers with different resonator setups and tested their performance. Twisting was introduced to fiber during drawing from an octagonal, CO2 laser-shaped or mechanically grinded preform so that the twist remained frozen in the drawn fiber. We have shown that the fiber twist significantly improves the pump absorption even in the case of straight or coiled fibers with large coil radii. We provide a preliminary comparison of two fiber laser resonators
Permanent Link: http://hdl.handle.net/11104/0330088