Thermo-optical properties of air-clad photonic crystal fiber lasers in high power operation

Abstract

We report on the investigation of the thermo-optical behavior of air-clad ytterbium-doped large-mode-area photonic crystal fiber lasers. Analytical and numerical models are applied to calculate the heat distribution and induced stresses in a microstructured fiber. The results are compared to conventional double-clad fiber lasers and design guidelines are provided to ensure maximum heat dissipation and scalability to power levels of several kWs.

Numerical modelling of self-heating effects on guiding modes of high-power photonic crystal fibre lasers

“…To generalize our modelling, the thermal dispersion and thermally induced stress effects will be taken into account for the first time. The latter is often ignored in literature [8,9,12,13,17]. Our fibre laser is an air-clad ytterbium-doped large-mode-area one used already by Limpert et al [8].…”

“…The latter is often ignored in literature [8,9,12,13,17]. Our fibre laser is an air-clad ytterbium-doped large-mode-area one used already by Limpert et al [8]. The core has been established with three holes missing in the triangular lattice round the inner clad.…”

“…where T(x, y) is temperature in Kelvin, K(T) is temperature dependent thermal conductivity in W/m/K, and Q(x, y) is heat source density in W/m 3 . Although temperature independent thermal conductivity may suffice [8,9,19,20], in this work we have used the experimental data of Jund and Jullien [21] to comprehensively cover the temperature dependence of thermal conductivity.…”

“…In this regard 2.3 m long ytterbium-doped air-clad large-modearea fibre lasers have been reported to deliver 80 W output power equivalent to the power density of 35 W/m [7]. Also, for a 4 m length fibre, a pump of 360 W delivering the output power of 260 W was reported [8].…”

“…Although a large surface-to-volume ratio of fibres can ease heat dissipation from the fibre surface compared to bulk lasers, however in high powers the heat transfer mechanisms cannot be such effective [8][9][10]. Accordingly, active cooling systems must be used.…”