Thermal effects and gain competition in Yb-doped large mode area fibers for high-power applications

Currently, the increase of output power of Yb-doped large mode area photonic crystal fiber lasers, fundamental for many practical industrial applications, is mainly limited by thermal effects, which negatively affect the beam properties. In this work the influence of the inner cladding characteristics on the guiding properties of Yb-doped symmetry-free photonic crystal fibers in different heating conditions has been investigated using simulation tools based on the finite element method. Simulation results have shown that, by properly modifying the inner cladding characteristics, it is possible to facilitate the coupling of the guided modes with the cladding ones, thus affecting their confinement in different heating regime.