Novel double-clad thulium-doped fibers for high power fiber lasers

Fiber lasers are generally considered as one of the youngest and most rapidly developing branch of lasers. Compare to other types of lasers, fiber lasers are appreciated for their excellent beam quality, good thermal management thanks to high surface to volume ratio, potential all-fiber setup and correspondingly low maintenance, high-average-output power and other advantages. The high-power operation of fiber lasers was enabled mainly by the invention of cladding pumping within a double-clad fiber structure [1, 2]. Such a fiber serves as an efficient transformer of the low-brightness, high-power radiation of the laser diodes (coupled into the large area inner cladding of the DC fiber) into a high-brightness, high-power laser beam coming out from the rare-earth-doped, narrow fiber core.

In this thesis, novel geometry and layouts of double-clad thulium doped fibers for high-power fiber lasers will be theoretically and experimentally studied. The research goal is to find ways and guidelines how to tailor the pump absorption along the active fiber so that the overall efficiency of the active fiber is increased. It involves design of the fiber cross section, including dopant distribution as well as optimization of fiber layout (including fiber bending, twisting and cooling). The recently developed, ceramic-nanoparticle doping method will be used for preparation of active fibers [3]. Thulium-doped fiber lasers will be tested in laboratory fiber laser setups emitting at around 1.9-2.05 µm.

References

[1] P. Peterka, "Double-clad fibers for high-power fiber lasers," in Proc. 9th EPS-QEOD Europhoton Conf., Prague, 30 Aug - 4 Sept 2020, Summer School Tutorial p. SS2.1. https://youtu.be/h17GjmLTjw4

[2] P. Koska, P. Peterka, and V. Doya, "Numerical modeling of pump absorption in coiled and twisted double-clad fibers," IEEE J. Sel. Top. Quantum Electron. 22(2), 4401508 (2016). http://doi.org/10.1109/Jstqe.2015.2490100

[3] M. Kamrádek, I. Kašík, J. Aubrecht, J. Mrázek, O. Podrazký, J. Cajzl, P. Vařák, V. Kubeček, P. Peterka, and P. Honzátko, "Nanoparticle and solution doping for efficient holmium fiber lasers [Invited paper]," IEEE Photonics J. 11(5), 7103610 (2019). http://doi.org/10.1109/jphot.2019.2940747