Enhanced pump absorption efficiency in coiled and twisted double-clad fibers for fiber lasers

24.09.2018, 14:00

Dr. Pavel Peterka, Institute of Photonics and Electronics, The Czech Academy of Sciences, Prague, Czech Republic

High-power operation of fiber lasers was enabled by the invention of cladding-pumping in a double-clad fiber structure. Pump absorption is enhanced by broken circular symmetry of inner cladding cross sections and by mode-scrambling of the pump modes by unconventional fiber coiling. However, theoretical studies were limited to the assumption of a straight fiber until recently, when the rigorous model accounting for fiber bending and twisting was described [1-3]. It was found that squeezing of the effective area of the pump radiation due to fiber bending plays important role in cladding-pump absorption enhancement. We review results of numerical modelling of pump absorption in various types of double-clad fibers, e.g., with cross section shape of hexagon, stadium, and circle; two-fiber bundle (so-called GTWave fiber structure) a panda fibers are also analyzed. The presented results can have practical impact in construction of fiber lasers: with pump absorption efficiency optimized by our new model (the previous models did not take into account fiber twist), the double-clad fiber of shorter length can be used in the fiber lasers and amplifiers. In such a way the harmful influence of background losses and nonlinear effects can be minimized. Less demanding cladding-mode-strippers can be used.

[1] Koška, P., Peterka, P., and Doya, V., "Numerical modeling of pump absorption in coiled and twisted double-clad fibers," IEEE J. Sel. Top. Quantum Electron., vol. 22, no. 2 (2016).

[2] Koška, P., Peterka, P., Aubrecht, J., Podrazký, O., Todorov, F., Becker, M., Baravets, Y., Honzátko, P., and Kašík, I., "Enhanced pump absorption efficiency in coiled and twisted double-clad thulium-doped fibers," Opt. Express, vol. 24, no. 1, pp. 102-107 (2016).

[3] Koška, P. and Peterka, P., "Numerical analysis of pump propagation and absorption in specially tailored double-clad rare-earth doped fiber," Optical and Quantum Electronics, vol. 47, no. 9, pp. 3181-3191 (2015).